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Substance Use and Peers During Adolescence and the Transition to Adulthood: Selection, Socialization, and Development

Abstract and Keywords

This chapter summarizes recent literature concerning the connection between peers and substance use (i.e., alcohol use, cigarette use, and illicit drug use) during adolescence and the transition to adulthood. The broad category of peers consists of a wide range of social relationships including best friends, peer groups, and crowds; important aspects include peer activities, relationships, and influence. Young people both select their friends (e.g., based on shared interests) and are influenced, or socialized, by their selected peers. When examining the dynamic periods of life that cover the transitions into, through, and out of adolescence and into the post-high school years, selection and socialization are especially important, given that many transitions involve changes in social contexts and peer relationships. The authors take a developmental perspective by focusing on the developmental transitions that occur during adolescence and the transition to adulthood and how they influence peer relations and substance use.

Keywords: Adolescence, transition to adulthood, selection, socialization, development, substance use


Imagine what substance use during adolescence and the transition to adulthood would be like if it were not a primarily social activity, but instead a solitary activity akin to reading a book or listening to music alone. Our job as researchers would be a bit easier because we would not have to attend to the multitude of complex peer-related interactions. No doubt, we would be much further along in understanding the etiology and prevention of substance use during adolescence and the transition to adulthood, and there probably would be less substance use in this population. And this chapter would be very short.

The fact is that substance use during adolescence and the transition to adulthood is inextricably interwoven with peer relations, activities, and influences. Very few adolescents use substances alone; instead, most use only when with their friends. As has been noted for decades, the interconnections between substance use and peers are complex, bidirectional, and a perfect illustration of the twin processes of selection and socialization (Kandel, 1980). There is no single answer to the question of why young people use substances, but it is clear that peers are a key ingredient. In fact, the convergence of heightened peer influence, drive for exploration, and introduction to substances makes this period a particularly important one for the study of peer influences on substance use.

It is no coincidence that both peer relations and substance use intensify during adolescence. Peers take center stage, providing consensual validation for the unique experiences of early adolescence (Sullivan, 1953), a safe haven from the adult-run worlds of families and schools, a sounding board for (p. 527) identity quests, a launching pad for romantic relations, and fuel and direction for sensation-seeking and risk-taking behaviors. Alcohol, tobacco, and illicit drug use are typically initiated during adolescence, with rates climbing quickly across middle and high school and into the transition to adulthood (Johnston, O’Malley, Bachman, & Schulenberg, 2012), and peers provide the opportunity and social context for substance use initiation and escalation. It is tempting to view this temporal co-occurrence of intensification of peer involvement and of substance use as suggesting a strong etiological connection, such that whatever makes peer involvement essential to the contemporary experience of adolescence also sets the stage for alcohol and other drug use. However, it is clearly not this simple. In fact, most adolescents have friends who do not condone drug use. Based on the 2011 national Monitoring the Future study, Johnston et al. (2012) found that among twelfth-graders, the majority (53%) reported that their friends would disapprove of them even trying marijuana. These rates of disapproval are much higher for younger age groups, more frequent use, and illicit drugs other than marijuana. Thus, peers help set the stage for both the use and nonuse of substances.

Our purpose in this chapter is to summarize recent literature concerning the connection between peers and substance use—as causes, correlates, and consequences—during adolescence and the transition to adulthood. We focus on substance use in the forms of alcohol use, cigarette use, and illicit drug use. The broad category of peers consists of a wide range of social relationships including best friends, peer groups, and crowds; important aspects include peer activities, relationships, and influence. As we argue, peer influences on substance use (and nonuse) tend to be more subtle and consensual rather than direct “peer pressure,” especially during late adolescence and the transition to adulthood. Central to understanding these more subtle peer influences are the processes of selection and socialization. Young people both select their friends—for example, based on shared interests—and in turn are influenced, or socialized, by their selected peers. When examining the dynamic periods of life that cover the transitions into, through, and out of adolescence and into the post-high school years, selection and socialization are especially important, given that many transitions involve changes in social contexts and peer relationships.

Peer linkages with substance use occur within a broader developmental context. In this chapter, we take a developmental perspective by focusing on the developmental transitions that occur during adolescence and the transition to adulthood and how they influence peer relations and substance use. To help frame consideration of the linkages between peers and substance use from a developmental perspective, we begin with a conceptual overview including consideration of the twin processes of selection and socialization. We then review the relevant literature, ordered developmentally from adolescence to the transition to adulthood. We conclude with consideration of overarching conceptual and empirical themes and directions for future research.

Conceptual Overview: Developmental Perspective on Peers and Substance Use

Our developmental perspective is founded on a broad interdisciplinary developmental science framework that emphasizes multidimensional and multidirectional developmental changes across the life course characterized by successive and dynamic mutual selection and accommodation of individuals and their contexts (Baltes, Lindenberger, & Staudinger, 2006; Cairns, 2000; Elder, 1998; Lerner, 2002; Sameroff, 2000). Both individuals and contexts are considered to play strong, active roles in the process of development. We also consider the importance of the person–context match, the connection between what the developing individual needs and what the context provides. During adolescence and the transition to adulthood, peers provide a key context for development in general and the development of substance use in particular.

Through the process of selection, individuals select available environments and activities based on personal characteristics, beliefs, interests, and competencies. Selected ecological niches then provide additional opportunities—and effectively limit other opportunities represented by niches not selected—for continued socialization and further selection. This progressive accommodation suggests the qualities of coherence and continuity in development. However, consistent with an emphasis on dynamic person–context interactions and multidirectional change, development does not necessarily follow a smooth and progressive function, and early experiences do not always have strong or lasting effects (e.g., Cairns, 2000; Laub & Sampson, 2003; Lewis, 1999; Rutter, 1996; Stouthamer-Loeber, Wei, Loeber, & Masten, 2004). Thus, both continuity and discontinuity are expected across the lifespan.

(p. 528) Several elements from this broad-based developmental perspective inform our efforts in this chapter, organized under the headings of continuity and discontinuity and developmental transitions. In this section, we first consider these elements and then offer a more developmentally informed perspective on selection and socialization.

Continuity and Discontinuity

Although continuity and discontinuity are central to the understanding of development (Kagan, 1980; Werner, 1957), they are not easily defined. Stability and continuity are sometimes used interchangeably, but among developmental scientists the two are generally viewed as related yet distinct. Typically, stability pertains to the extent to which individuals maintain relative rank ordering over time, and continuity pertains to the course of intraindividual trajectories (e.g., Baltes, Reese, & Nesselroade, 1977; Lerner, 2002). Furthermore, two uses of the concepts of continuity and discontinuity are common (Schulenberg, Maggs, & O’Malley, 2003; Schulenberg & Zarrett, 2006), and both are relevant to understanding interconnections between peers and substance use during adolescence and the transition to adulthood.

First, continuity and discontinuity can be considered in terms of causative linkages across the lifespan (e.g., Lewis, 1999; Masten, 2001). Ontogenic continuity reflects a progressive and individual coherence perspective in which earlier events and experiences are viewed as formative and essentially causing future outcomes (cf., Caspi, 2000; Roberts, Caspi, & Moffitt, 2001). Across the lifespan, ontogenetic continuity tends to prevail, but it is not necessarily the case that early functioning determines later functioning (Cicchetti & Rogosch, 2002; Lewis, 1999; Martin & Martin, 2002). Instead, the effects of early experiences may be amplified, neutralized, or reversed by later experiences (Schulenberg & Zarrett, 2006). This focus on more developmentally proximal influences reflects an ontogenic discontinuity perspective, whereby functioning is assumed to be due more to recent and current contexts and experiences than to early experiences (Lewis, 1999). This general theme of indeterminacy in the developmental course because of powerful proximal influences is consistent with the life course literature suggesting the power of developmental transitions in altering the course of substance use (Bachman et al., 2002; Schulenberg, O’Malley, Bachman, & Johnston, 2005). The distinction between ontogenetic continuity and discontinuity is important to consider when examining peer influences on substance use. For example, ongoing childhood difficulties that culminate in involvement with deviant peers in adolescence likely reflect ontogenetic continuity (e.g., life-course–persistent antisocial behavior in Moffitt, 1993), and peer influences may be viewed more in terms of selection. In contrast, a positive developmental trajectory during childhood followed by involvement with substance-using peers in adolescence likely reflects ontogenetic discontinuity (e.g., adolescent-limited antisocial behavior in Moffitt, 1993), and peer influences may be viewed more in terms of socialization.

The second use of continuity and discontinuity is consistent with an organismic developmental perspective in which discontinuity is viewed as reflecting qualitative or underlying structural-level change (e.g., the emergence of new structure or meaning; e.g., Piaget, 1970; Werner, 1957). Continuity and discontinuity can be considered as having both descriptive components (pertaining to manifest behaviors) and explanatory components (pertaining to underlying purposes, functions, and meanings; e.g., Kagan, 1969; Lerner, 2002). Homotypic continuity refers to the presence of both descriptive and explanatory continuity (Caspi & Roberts, 1999; Kagan, 1969) whereby both a given behavior (e.g., verbal bullying of peers) and the underlying purpose of that behavior (e.g., to maintain place in the social hierarchy) remain continuous over time (e.g., across childhood into adolescence). Often, however, behaviors vary across time while the underlying purpose or meaning of those varying behaviors remains the same. For instance, the young adolescent who bullies to maintain her place in the social hierarchy may find other more subtle manipulation patterns that serve the same purpose in young adulthood. This is termed heterotypic continuity (i.e., descriptive discontinuity, explanatory continuity; Caspi & Roberts, 1999; Kagan, 1969). More generally, adaptation to life’s tasks may be continuous, but many of the activities and behaviors associated with adaptation tend to be discontinuous (Masten, 2001; Moffitt & Caspi, 2001; Rutter, 1996). Functional discontinuity, which may be considered the opposite of heterotypic continuity, occurs when the manifest behavior appears unchanged yet the underlying function or meaning of that behavior changes over time (i.e., descriptive continuity, explanatory discontinuity). For example, a 14-year-old adolescent uses marijuana primarily for the purpose of having fun with friends; 10 years later, he still uses marijuana, but the main purpose is to attempt to (p. 529) cope with anxiety. The concepts of homotypic continuity, heterotypic continuity, and functional discontinuity can be useful in parsing the connections between peers and substance use. For example, consistent with heterotypic continuity, being successful in peer relations may be continuous from childhood into adolescence but what it takes may shift over time and may cross into deviant activities during adolescence (Allen, Porter, McFarland, Marsh, & McElhaney, 2005).

Developmental Transitions

Developmental transitions include major transformations in individuals, their contexts, and the relations between individuals and their contexts across the life course (e.g., Bronfenbrenner, 1979; Graber & Brooks-Gunn, 1996; Schulenberg & Maggs, 2002). They often are viewed globally as the connections between major life periods (e.g., transition to adolescence, transition to adulthood). Developmental transitions include a series of specific changes that can be viewed as internally based (e.g., biological, physical, cognitive, emotional, and identity-related) and externally based (e.g., attainment of adult legal status, beginning full-time employment, changing role from fiancé/fiancée to spouse; Rutter, 1996). The period beginning with the transition into early adolescence and ending in the transition to adulthood arguably constitutes one of the most dynamic 10–15 years in the lifespan in terms of internally based and socially based developmental transitions.

Issues of continuity and discontinuity are central to understanding the power of major developmental transitions on individuals’ lives (Rutter, 1996). In the domain of substance use, transitions can contribute to ontogenic discontinuity in ongoing trajectories in several ways, such as by overwhelming coping capacities, by altering the person–context match, and/or by increasing vulnerability to chance events (Schulenberg et al., 2003; Schulenberg & Zarrett, 2006). By providing “shocks to the system,” transitions can serve as proximal effects that either amplify or counteract developmentally distal effects. The result of such shocks or alterations in person–context match can range from turning points that result in long-term changes in course (Elder, 1998; Ronka, Oravala, & Pulkkinen, 2002; Rutter, 1996) to developmental disturbances that reflect only momentary perturbations yielding a jumbling of individual differences for a limited time (Schulenberg & Zarrett, 2006).

Discontinuity engendered by turning points, Rutter (1992) suggests, is most likely to occur when the transition events and experiences are drastically different from those prior to the transition. For example, the transition to residential college is associated with increased binge drinking and other drug use in part because of change in living situation (i.e., no parents, surrounded by age-mates; e.g., Bachman, Wadsworth, O’Malley, Johnston, & Schulenberg, 1997; Schulenberg & Maggs, 2002). Similarly, entry into marriage and other adult roles relates to declines in substance use, including for many of those who were heavily involved in alcohol and other drug use (e.g., Bachman et al., 2002; Bartholow, Sher, & Krull, 2003; Staff et al., 2010). In contrast, some discontinuity may best be viewed as a developmental disturbance or a short-term perturbation. Once individuals are given time to adjust, they might resume their prior, ongoing trajectory. In such cases, a major transition may simply result in short-term deviance (e.g., increased binge drinking, affiliation with a more deviant peer group) and not have long-term effects on developmental course or predict later functioning in adulthood (Schulenberg et al., 2003; Schulenberg & Zarrett, 2006).

Although the power of transitions may be more obvious in the case of discontinuity, transitions also contribute to our understanding of continuity, with transitional experiences serving as proving grounds that help consolidate and strengthen ongoing behavioral and adjustment trajectories for better and worse (Schulenberg & Zarrett, 2006). Individuals tend to rely on intrinsic tendencies and known behavioral and coping repertoires in novel and ambiguous situations (e.g., Caspi, 2000; Dannefer, 1987), suggesting that young people already experiencing difficulties may have trouble negotiating new transitions and fall further behind their well-functioning peers. In contrast, those already doing well have the resources to deal successfully with new transitions and climb further ahead of their age-mates having difficulties (Schulenberg et al., 2003). Thus, during major transitions such as the transition into middle school or high school, substance use patterns may change or become more solidified; similarly, such transitions may serve to intensify peer relations, such that young people rely more on their friends experiencing the same transition.

In addition, despite major life transitions, important contexts may change little. If one does not leave the parental home after high school and thus maintains similar relationships (good or bad) with family members and peers, then the person–context match (p. 530) or mismatch may be maintained across the transition, contributing to some continuity in substance use trajectories. In addition, continuity often occurs even if important relational contexts do change, for example due to geographical mobility, because one may still select into similar types of relational contexts, such as similar peer groups (e.g., Collins & van Dulmen, 2006; Furman, Simon, Shaffer, & Bouchey, 2002; Reis, Collins, & Berscheid, 2000). For example, Schulenberg and colleagues (Schulenberg, O’Malley, Bachman, Wadsworth, & Johnston, 1996; Schulenberg et al., 2005) found that those who maintained either high or low levels of substance use from high school through the transition to adulthood reported similar levels of peer substance use across this time, regardless of whether their peer groups changed (e.g., due to leaving home for college), suggesting that continuity in substance use corresponds to continuity in peer contexts or person–context matches.

Specific Theoretical Perspectives on Peers and Substance Use

In addition to the broad developmental perspective as a framework, several more specific theories have been applied to the study of peers and adolescent substance use. Our view is that these important theories concern mechanisms and processes that occur within the developmental framework just described. We briefly summarize some of these theories here and then illustrate various aspects of them when summarizing the empirical literature. Theories of social selection and friendship formation include the proximity principle, which suggests that individuals with similar characteristics who share proximity tend to affiliate with one another (Verbrugge, 1977); thus, transitions that continue or disrupt proximity can contribute to continuities and discontinuities in peer relations and influences. Problem behavior theory (Jessor & Jessor, 1977) identifies potential proximal and distal social influences, as well as the importance of personal characteristics (Chassin, Hussong, & Beltran, 2009; Petraitis, Flay, & Miller, 1995); individual characteristics operating within a peer context contribute to the accumulation (and eventually dispersal) of problem behaviors over time (Jessor, Donovan, & Costa, 1991). Influences of family and peers are theoretically important, distally in terms of attachment and proximally as a result of social modeling. This aspect of problem behavior theory is similar to social learning theory, which contends that delinquency is learned through imitation and differential reinforcement (Akers, 1999). Delinquency research, founded in differential association theory, emphasizes the importance of socialization on changes in attitudes (Reed & Rountree, 1997). Kobus (2003) provides a review of the application of social learning theory, primary socialization theory, social identity theory, and social network theory to the role of peers in adolescent substance use. Dishion and colleagues (2008) provide a review of three developmentally based hypotheses regarding peer influences: social augmentation, arrested socialization, and intrasubjectivity.

Selection and Socialization in a Developmental Perspective

Researchers have long noted that friends tend to share similar characteristics, interests, behaviors, and preferences. This homophily can be explained through two primary processes: selection and socialization (e.g., Brechwald & Prinstein, 2011; Kandel, 1978; Prinstein & Dodge, 2008). Selection reflects the extent to which individuals choose to affiliate with peer group members who are similar to themselves (i.e., “birds of a feather flock together”). That is, adolescents have the freedom to spend time with different peers while at school, join different after-school activities such as sports teams or social groups, and make choices about which friends to contact in their free time. Which individuals adolescents choose for interaction undoubtedly accounts for at least some of the similarity between friends. In addition, socialization accounts for the variety of ways in which adolescents influence each other to become more similar over time. The domains of these influences range from relatively superficial (e.g., clothing and music preferences) to potentially harmful (e.g., substance use) lifestyle decisions. Repeated exposure to peer influences over time accumulates to impact individuals across development (Brown, Bakken, Ameringer, & Mahon, 2008). Peer influences are particularly complex, given that they are both multidimensional and multidirectional (Brown et al., 2008). For example, individuals not only choose their friends, but they also have to be reciprocally chosen to form a close relationship. Adolescents are required to both make selections about peer involvement and modulate responses to peer socialization influences, which is especially challenging in times of change.

It is indisputable that both selection and socialization are operating together to account for peer similarity in drug use. It is even fairly clear that (p. 531) selection and socialization work reciprocally over time, but the process, relative strength, and mechanisms of these influences are not yet well understood. Schulenberg et al. (1999) propose a process of “selection-based socialization” whereby those who are deviant-prone seek out others who are also deviant-prone (selection), and together the deviant-prone adolescents influence each other through shared experiences (socialization). These shared experiences then consolidate deviancy, which limits experiences with other peers and intensifies experiences with current peers.

The interlinked processes of selection and socialization largely reflect ontogenic continuity, but developmental transitions have the potential to interrupt some of the selection–socialization linkage over time and lead to ontogenic discontinuity. Thus, especially during school-related transitions (into middle school, high school, and post-high school experiences) when there are changes in available peers, selection and socialization processes have the potential to start anew. During such transitions, to the extent that young people have a wide range of available choices of friends, selection may be particularly powerful initially. As mentioned earlier, during the transition to college when friendship choices are presumably more flexible, young people typically select friends similar to those from high school in terms of substance use involvement (i.e., continuity). In contrast, to the extent that choices are limited during transitions, socialization may initially prove to be more powerful, creating the potential for discontinuities in substance use. Thus, each transition has the potential to consolidate selection–socialization linkages, yielding continuity in substance use trajectories, or to disrupt the ongoing reciprocal selection–socialization processes by providing new contexts, new selection targets, and new socialization experiences, yielding possible discontinuity in substance use trajectories. In the next sections, we review concepts regarding the social contexts adolescents experience and then empirical evidence pertaining to selection and socialization during adolescence and the transition to adulthood.

Social Contexts During Adolescence

The study of adolescence has become increasingly focused on the many important micro- and macrolevel contexts that work together to structure the adolescent experience and interact with individual characteristics to set the course of development (Lerner & Steinberg, 2009). These include, for example, families, peers, schools, and work settings, as well as neighborhoods, communities, cultures, and ultimately historical settings. All of these social and broader cultural contexts relate to adolescent substance use (e.g., Chassin et al., 2009), but it is fair to say that peer-related contexts are especially pivotal. It is also important to understand how peer contexts relate to other microcontexts such as families and schools (i.e., the mesosystems in Bronfenbrenner’s theory of human ecology, 1979) and how these interactions help predict adolescent substance use.

Just as characteristics of the individual affect his or her responses to peer influences, characteristics of friend groups are also key components of peer relationships. Social network analyses and other similar methods point to the importance of friendship reciprocity, hierarchy, and status among peers. Understanding various peer contexts is important for differentiating the roles of peers in adolescents’ lives.

Schools and Peer Crowds

Socialization of adolescents takes place within the broader context of schools (Fujimoto & Valente, 2012). Cleveland and Wiebe (2003) analyzed data from adolescents in the National Longitudinal Study of Adolescent Health (Add Health). Using hierarchical linear modeling (HLM) to describe students within schools, the authors found that the strength of association between individual and peer levels of substance use varied by school level of use, especially for cigarettes (Cleveland & Wiebe, 2003). In other words, the overall level of substance use in an adolescent’s school was an important factor, such that some schools provided adolescents greater opportunities to be involved with substance-using peers than other schools. Schools can also serve a protective function: positive school climate and a sense of community within the school have been found to protect against substance use by moderating the association between peer influence and substance use, thereby serving as a protective factor against substance use (Mayberry, Espelage, & Koenig, 2009).

Similarly, the effect of peers on substance use varies by peer crowd membership. In some peer crowds (e.g., “low-status,” “troublemakers,” “hot shots,” and “burnouts”; see Kobus, 2003, for a review) teens are more likely to smoke than in other peer crowds. However, the influence of peer crowds decreases during middle and late adolescence, as close friends and romantic partners become more (p. 532) important (Brown, Dolcini, & Leventhal, 1997; Brown & Larson, 2009). In addition, adolescents become more selective of their friends as they age, and the number of reciprocal friendships decreases and the intimacy of friendships increases (Aboud & Mendelson, 1998).

Social network analysis is a powerful technique used to capture the characteristics of a social group that may moderate the processes of influence that occur within it. Peer nomination processes are used to ascertain the size and connectedness of peer groups as well as target each individual’s sociometric position: membership in a social group, a dyadic friendship, or as an isolate. Generally, mutual nominations are used, such that a group member receives several mutual nominations, a dyad member receives one, and an isolate receives none. In one such study of 13- and 15-year-olds, popularity and expansiveness of one’s peer group were examined as predictors of substance use (Pearson et al., 2006). Both popularity and expansiveness of peer network positively related to substance use, with the most popular adolescents and those with the most expansive networks being the heaviest substance users.

Also using social network analysis, Ennett et al. (2006) found that individuals who were less embedded in their peer network, had higher status, or had closer proximity to substance-using peers were more likely to use substances. On the level of peer networks, they found that members of less dense networks were more likely to smoke cigarettes and use marijuana. Overall, Ennett et al. (2006) conclude, “Conventionality of relationships—having friends in the network, being liked but not too well liked, and having fewer friends who use substances—is most beneficial” (p. 183).

Friendship reciprocity appears to moderate the effects of peer socialization on substance use. Mercken et al. (2007) showed that the influence of friends depended on the reciprocity of the relationship. In nonreciprocal friendships, the similarity of friends’ smoking behavior was explained by selection only, with no effect of socialization. In reciprocated friendships, both selection and socialization explained similarity of smoking behavior. Adolescents who are marginal to a group likely have more freedom to make choices about their behavior, either for or against substance use (Kobus, 2003). However, nonreciprocal or unidirectional friendships may be particularly strong contexts for adoption of a friend’s behavior, particularly when the status of the two friends differs. Bot et al. (2005) found that differences in status were particularly important in explaining change in drinking behavior. In cross-sectional analyses, respondents’ drinking behavior most resembled that of their reciprocal friends. In longitudinal analyses, change in respondents’ drinking behavior appeared to conform to the drinking behavior of a unilateral friend of higher status, perhaps out of desire to achieve acceptance from a higher status peer (Bot, Engels, Knibbe, & Meeus, 2005).

Peer Pressure

There is a widely held belief that peer group similarity is due in large part to peer pressure (see Urberg, Cheng, & Shyu, 1991). Overt peer pressure, however, does not appear to play a significant role in adolescent substance use in either cross-sectional or reciprocal models (Reed & Rountree, 1997). Arnett (2007) concludes, based on qualitative findings, that “direct peer pressure is rare, and when it occurs it is often rejected as a violation of the principles of friendship and as an infringement of the adolescent’s independence and freedom of choice” (p. 601). Rather, selection into groups with similar characteristics and exposure to substance use–tolerant attitudes and beliefs from peers help explain adolescent substance use (Mason, Mennis, Linker, Bares, & Zaharakis, 2013). In a review of the literature regarding peers’ influences on adolescent smoking behavior, Kobus (2003) asserts that pressures to smoke are predominately normative rather than coercive in nature. In other words, adolescents often experience internal self-imposed pressure to smoke in order to garner social approval and fit in with a valued social set (Nichter, Nichter, Vuckovic, Quintero, & Ritenbaugh, 1997). Therefore, influences from peers who encourage substance use are mostly through modeling, exposure to substance use, and imitation (Kobus, 2003).

Individual Characteristics

Not all adolescents respond equally to peer influences (Allen, Chango, Szwedo, Schad, & Marston, 2012). The effects of peer processes may vary based on individual differences in personality and attitudes toward peers (Mason et al., 2013). Girls tend to be more influenced than boys by interpersonal influences, including both peers and families (Kandel, 1985). However, there is some evidence that, especially during mid-adolescence, girls are more resistant to peer influence than are boys (Sumter, Bokhorst, Steinberg, & Westenberg, 2009). Same-gender friendships tend to have a mutual influence pattern, but boys in mixed-gender (p. 533) adolescent friendships tend to more strongly influence their female friends (Gaughan, 2006). When gender differences have been found among young adults, men have been shown to be more similar to and influenced by their friends than are women (Andrews, Tildesley, Hops, & Li, 2002). Therefore, it is important to take into account both gender and age in order to understand the level of peer influence on behavior.

Individuals differ in their susceptibility or openness to influence (Brown et al., 2008). For example, those with social anxiety tend to be more influenced by their peers, at least among girls (Prinstein, 2007). Susceptibility to peer influence has been found to moderate the effects of peer socialization. For example, susceptibility to peer pressure assessed in a laboratory interaction with adolescents’ best friends was found to predict concurrent substance use (Allen, Porter, & McFarland, 2006). Additionally, higher levels of susceptibility during early waves predicted greater responses to negative peer pressure in later waves, according to best friends’ reports of the influence they exerted on the target adolescent’s behavior. There was a significant interaction between susceptibility to influence and peer alcohol use, such that only those high in susceptibility who had substance-using peers showed high levels of substance use; those low in susceptibility and those with nonusing peers showed low or no substance use.

Schulenberg et al. (1999) modeled the reciprocal relationships among susceptibility to peer pressure, exposure to peer drinking, and one’s own overindulgence in drinking (i.e., lack of control while drinking, negative consequences of drinking), in a three-wave longitudinal study of adolescents in grades six through eight. Several alternative models were tested, including susceptibility-driven, exposure-driven, overindulgence-driven, direct effects of susceptibility and exposure on overindulgence, and exposure- or susceptibility-mediated models. The exposure-mediated model, in which exposure to peer drinking mediated the relationship between susceptibility to peer pressure and overindulgence, provided the best overall fit. Additional analyses were performed to test whether initial susceptibility moderated the relationship between exposure and overindulgence. There were no significant cross-lag effects between exposure and overindulgence in the low-susceptibility group, whereas those in the high-susceptibility group showed significant reciprocal cross-lag effects between exposure and overindulgence. Thus, the typical reciprocal relationships over time between peer use and one’s own use operate only when one is highly susceptible to peer influence. Allen et al. (2012) report complementary findings, demonstrating that susceptibility to peer influence, as reflected in changes in adolescents’ substance use in accordance with their peers’ baseline levels of use, was predicted by previous lack of autonomy and social support, low refusal skills, and low levels of social acceptance of a close friend.

Developmental timing is also important to consider for the level of susceptibility and influence peers have on each other. From childhood across adolescence, peer relations become more complex, moving from activity-based “play dates” to more all-encompassing relationships. Sullivan (1953) argues that the period of early adolescence is best negotiated by those who form “chum-ships,” close nonsexual intimate relations that provide consensual validation of the rapid and intense experiences of this period. Resistance to peer influence and peer pressure increases across adolescence (ages 14–18 in Steinberg & Monahan, 2007; ages 10–18 in Sumter et al., 2009). This suggests that adolescence, and in particular middle adolescence, is an important window of opportunity to foster a sense of self and identity so that individuals will be able to resist negative peer influences and make healthier behavioral choices. The ways in which adolescents relate to and are influenced by their peers is dynamic and changes across development. Both these interindividual differences and intraindividual differences are important considerations for models of peer influence.

The impact of peers likely also varies with level of substance use experience. For smoking behavior, there is evidence that peer groups have a greater impact on initiation of use, whereas best friends have a greater influence on maintenance of smoking behavior (Kobus, 2003). Once adolescents have begun to experiment with alcohol and marijuana, for example, the most dominant social influence is the modeling and imitation of peer use (Kandel, 1985). Again, the developmental timing is important to consider because the influences of peers from early adolescence through the transition to adulthood may change in complex ways.

Peers as Compared to Family

As with peer use, the direction of influence of parents tends to be assumed to be consistent in valence. However, parents can have deviant influences just as peers can have positive influences on substance use in adolescence (Kandel, 1996). In (p. 534) addition, adolescent peer groups differ in the degree to which they accept or reject parental involvement (Kandel, 1985).

It is likely that parental and peer influences work together over time in contributing to adolescent drug use, reciprocally influencing each other through developmental cascade patterns (Dodge et al., 2009; Lynne-Landsman, Bradshaw, & Ialongo, 2010). Dodge et al. (2009) describe a developmental cascade in which early deficiencies in parenting contributed to early behavioral difficulties and poor peer relations, which in turn contributed to parents backing away and monitoring less during early adolescence, which led to more time with deviant peers and greater likelihood of illicit drug initiation. This reflects ontogenic continuity, in which early risk factors across family, behavior, and peer systems gather together and mutually influence each other over time such that later difficulties prove to be highly predictive. But as Dodge et al. (2009) discuss, it is possible that the ongoing behavior trajectory toward adolescent drug use can be interrupted, say by increased monitoring and more effective parenting at early adolescence resulting in less time with deviant peers. In addition, it is possible that the peer context during early adolescence can itself contribute to ontogenic discontinuity, either by exerting a prosocial influence to counter earlier parenting deficiencies or exerting a negative influence to counter earlier positive parenting.

Both parents and peers provide important influences on adolescent decision making. Aseltine (1995) states, “the conclusion that parental influences are very limited, and are indeed secondary to peer influences, seems inescapable” (p. 115). However, Kandel (1996) cautions that parental influences have been underestimated and peer effects have been overestimated. Given the transience of adolescent peer relationships, parents may have the opportunity to provide more stable and lasting influences on their adolescent children (Kandel, 1985). Adolescents who report that their parents are more involved in their lives also report that they are less influenced by their peers (Wood, Read, Mitchell, & Brand, 2004), suggesting a potential protective effect. Like peer effects, the relative impact of parents’ influence may also vary by stage of the adolescent’s substance use. According to Kandel (1985), peers play an especially important role for initiation of marijuana use, and parental factors tend to have greater impact in the transition into other illicit drugs.

Although peer influences tend to affect lifestyle choices, parents tend to have a greater impact on values and aspirations (Kandel, 1985; 1996). Parent behaviors and attitudes continue to be associated with youths’ substance use, although the impact of peers predominates during adolescence. It is likely that parents’ influence is in laying a foundation for decision making and peer selection that sets the stage for adolescent choices (Buu et al., 2009; Kandel, 1996; Kobus, 2003, Van Ryzin, Fosco, & Dishion, 2012).

Other adolescents in the home provide an additional peer-type network for adolescents that should not be ignored. Siblings sometimes share friends, and siblings, especially older siblings, provide strong influences on adolescent substance use (Whiteman, Jensen, & Maggs, 2013). When sibling substance use behavior was taken into account, the effect of parents’ smoking behavior on eighth-graders’ smoking became nonsignificant (Mercken et al., 2007). Furthermore, siblings’ smoking behavior also had a significant influence on the reciprocal newly chosen and long-standing friends of their sister or brother the following year, illustrating the important, yet often neglected, role that siblings play in substance use behavior.

Peer Selection and Socialization in Adolescence

During adolescence, peers spend increasingly more time together and become more important to each others’ lives (Brown et al., 1997; Steinberg & Morris, 2001). Adolescence is characterized by escalation in the importance of peers in shaping behavior and in engagement in new, exploratory behaviors (Smetana, Campione-Barr, & Metzger, 2006). This developmental period also often includes the initiation of substance use (Maggs & Schulenberg, 2005). During the initiation phase of substance use, peers may also be particularly influential (Kandel, 1985) by modeling substance use behavior and ascribing social status to substance users.

As reviewed by Kandel (1985), adolescent friendships are characterized by the most similarity between friends on sociodemographic characteristics. Second in importance, however, are behaviors such as drug use. Early work by Kandel (1978) suggests that homophily, or similarity in drug use, results from peer selection and socialization influences that increase over time. However, Kandel’s later work (e.g., Kandel, 1996) cautions that earlier research on peer influences may have greatly overestimated the impact of peers because the (p. 535) work largely relied on cross-sectional self-reports of peer behaviors, rather than surveying peers themselves. Nonetheless, more recent work also shows the impact adolescents have on their peers. For example, Ennett and Bauman (2006) used social network analysis to assess similarity in smoking behavior among peer groups (i.e., cliques) and how such similarity develops. Analyzing data from adolescents in the same peer group in ninth grade and 1 year later in tenth grade, nonsmoking students in smoking cliques were much more likely to become smokers than nonsmoking students in nonsmoking cliques, thus illustrating peer socialization effects. On the other hand, Kiuru et al. (2010) find peer socialization to operate more strongly for alcohol use, and for cigarette smoking to be more attributable to selection effects.

Although the majority of empirical research emphasizes the dual processes of selection and socialization, some evidence emphasizes that adolescents with tendencies toward delinquent behaviors, including substance use, select friends with similar tendencies and behaviors. Dobkin et al. (1995) studied the early onset of substance use in boys aged 6–13 to determine whether early individual characteristics such as hyperactivity and oppositionality predicted selection of friends with similar characteristics. To determine whether selection of like peers or socialization by deviant peers predicted substance use, they tested models representing each scenario. In the first model, friends’ deviant characteristics were tested as predictors of boys’ later substance use. In the second, boys’ substance use was tested as a predictor of friends’ later substance use. The final model included mutual influences (i.e., socialization) of boys on their peers and vice versa. The best-fitting model was that in which boys’ early levels of deviant behavior predicted both their own substance use and the deviant behavior (i.e., fighting, gang membership, and arrests) of their friends during early adolescence. The authors concluded that deviant youth sought out similar friends after developing their own deviant habits (Dobkin, Tremblay, Masse, & Vitaro, 1995). Similarly, in a re-examination of previous studies claiming to support peer socialization processes as the mechanism of smoking initiation, Arnett (2007) found that most such studies did not account for initial friend characteristics, which may reflect selection of like peers. Reviewing past qualitative studies of early and middle adolescents, he concluded that peer socialization, when it did occur, seemed to work in the direction of discouraging cigarette smoking, although he notes that this may reflect substance-specific norms and disapproval surrounding cigarette use. Given the complexity of peer influences during adolescence, qualitative methods can be helpful in exploring peer processes in greater depth.

There is also some research supporting peer socialization as the primary mechanism of peer influence on substance use in early adolescence. Advances in statistical modeling have allowed for the simultaneous modeling of individual change in substance use and reciprocal influences between one’s own substance use and that of one’s peers (Steglich, Snijders, & Pearson, 2010). Using latent growth modeling, Wills and Cleary (1999) found that initial level of peer substance use was positively related to growth in adolescents’ substance use from sixth through ninth grade. They also noted several predictors (i.e., difficult temperament, poor self-control, and deviance-prone attitudes) of greater initial level of substance use in adolescents and their peers. This may indicate that adolescents selected peers who were like them in characteristics predicting substance use behaviors prior to the study’s initiation. Similar results were reported by Sieving, Perry, and Williams (2000), who found that higher levels of friends’ substance use predicted increased substance use by study participants from seventh to ninth grade.

The selection and socialization processes are reciprocal and often operate simultaneously (Reed & Rountree, 1997). Thornberry (1999) contends that the result can be a spiraling effect, such that individuals who exhibit delinquent behavior become more involved with delinquent peer groups and delinquent values, which then lead to more severe levels of behavior (similar to Schulenberg et al.’s selection-based socialization described earlier). To adequately separate the effects of selection and socialization, prospective studies are necessary. Otherwise, the “effect” of peer group confounds adolescents’ choice of like-minded peers and the influence of peers on changes in adolescents’ lives (e.g., Aseltine, 1995).

Research on peer processes in initiation and growth in substance use during adolescence has generated support for both selection and socialization mechanisms (e.g., Kandel, 1985; Kobus, 2003; Mercken et al., 2007). Perhaps not surprisingly, most studies find evidence for both selection and socialization processes in the development of substance use during adolescence, although the majority of work in this area is inconclusive regarding which influence holds greater importance. A study (p. 536) by Simons-Morton (2007), for example, used latent growth curve modeling to describe the influences of the initial level of substance use of adolescents and their friends (intercepts) on the changes in substance use of adolescents and their friends (slope). The author interpreted the results as evidence for both selection (i.e., intercept of adolescent use was associated with growth in substance-using friends) and socialization (i.e., intercept of friends’ use was associated with growth in adolescents’ own substance use). Ennett and Bauman (1994) assessed cigarette smoking in a two-wave study of eighth- and ninth-grade students. Using social network analysis, they found that, for peer group members, selection and socialization processes contributed relatively equally to homogeneity of smoking behavior in the peer group. However, most smokers were isolates, not peer group members, meaning they were loosely connected to a peer group or not connected at all. For these isolates, smoking behavior was best explained by deselection, in which smokers moved out of nonsmoking networks.

Using a combined cross-lag and latent growth model, Simons-Morton and Chen (2006) also found evidence for both selection and socialization mechanisms. However, these authors found more consistent evidence for socialization. In the growth model, selection effects were indicated by the finding that initial substance use in grade six predicted an increase in number of friends who used substances by grade nine. Socialization effects were supported by the finding that initial number of friends who used substances predicted increases in substance use over time. In the cross-lag model, the path from participant use to peer use was significant only from seventh to eighth grade, and the path from peer use to participant use was significant from each grade to the next, across the period of sixth to ninth grades.

Similarly, Urberg et al. (2003) found more evidence for socialization than selection effects. A two-stage model of peer influences on substance use (i.e., cigarette smoking and alcohol use) was proposed. The first stage was acquisition of a peer context (selection), followed by conforming (or not) to peers’ behaviors (socialization; Urberg, Luo, Pilgrim, & Degirmencioglu, 2003). Socialization was examined by controlling for the individual’s level of substance use at the first of four waves (and in effect controlling for any shared variance in substance use with peers at that time, which would constitute selection effects). No individual differences were found to differentiate those adolescents who acquired alcohol-using friends over the course of the study from those who did not (i.e., no selection effects). That is, all adolescents were equally likely to select alcohol-using friends over the course of the study. How much the adolescent valued academics and amount of time spent with parents were negative predictors of selecting friends who smoke. Socialization, or degree to which adolescents conformed to their peers’ substance use behavior, was positively predicted by high peer acceptance and high friendship quality. In sum, the majority of adolescent research supports both selection and socialization, to varying degrees, highlighting the complexity of peer relationships across development.

Positive Influences

Importantly, although peers are often assumed to have a role in promoting substance use, adolescent peers may also have a positive influence in deterring use (Berndt, 1992; Brown & Larson, 2009; Kobus, 2003). Adolescents can provide influences both toward problem behaviors and toward positive and prosocial behaviors (Allen & Antonishak, 2008). Youth who are isolated from peer groups are the most likely to smoke (Ennett & Bauman, 1993), suggesting that peer groups can operate as protective influences for substance use (Kobus, 2003). Although direct pressures to use substances are rare, it seems that peers may be more likely to use coercion to stop their friends from smoking and deter use (Kobus, 2003; see also Stanton, Lowe, & Gillespie, 1996, Urberg, Shyu, & Liang, 1990). These efforts to deter substance use provide yet another example of the dynamic nature of peer relationships and their associations with substance use behaviors.

Social Contexts of the Transition to Adulthood

The years following the end of secondary education bring profound changes in virtually every domain of life, whether the individual continues in full- or part-time education or pursues a more traditional, faster track to adult roles (Bynner, 2005; Maggs, Jager, Patrick, & Schulenberg, 2012; Schoon, Chen, Kneale, & Jager, 2012; Settersten, Furstenberg, & Rumbaut, 2005). In this review of links between substance use and peers during this phase of life, to the extent permitted by the extant literature, we make an important distinction between general population studies and those focused only on full-time college students. This distinction reflects a desire to describe the general (p. 537) population, rather than focusing exclusively on the college student population in which the majority of research is conducted. In addition, we have chosen not to describe this age period as emerging adulthood. Arnett (2000; 2006) proposed a theory of emerging adulthood to describe this period of the lifespan for individuals who often delay the adoption of adult roles, such as marriage and parenthood—one that is “distinguished by relative independence from social roles and from normative expectations” (Arnett, 2000, p. 469). However, in this chapter, this term is not used because this freedom may not be a universal experience. In fact, variations in culture, location, economic status, ability, and social role responsibilities (e.g., teenage parenthood) likely affect the experience of exploration (Bynner, 2005; Côté, 2000; Côté & Allahar, 1996; Shanahan, Porfeli, Mortimer, & Erickson, 2005). To more inclusively describe this developmental period, we use the term transition to adulthood.

We begin with a brief summary of the major characteristics of the post-high school period to lay the contextual groundwork for the associations between peer relations and substance use, noting similarities and differences between adolescence and the transition to adulthood, as well as between those who attend college and those who do not. Broad theoretical and methodological approaches for understanding and modeling the influence of peers on substance use are relevant to all ages of the lifespan, but there are undoubtedly important features of this developmental period that differ from early and middle adolescence. Following this discussion, the next section reviews research that has examined selection and socialization processes in links between peer involvement and substance use during the transition to adulthood.

The end of secondary education heralds the end of childhood dependence on parents and caregivers. Clearly, autonomy and self-determination show significant growth during adolescence, but the end of compulsory education coincides with major normative social, legal, and personal expectations and capabilities. Universal institutional structure tends to fall away for most (Schulenberg & Maggs, 2002), and the imperative for self-direction in life decisions, large and small, increases (Aseltine & Gore, 1993; Shanahan, 2000). With this comes the freedom to spend more unsupervised time with peers and the ability to select into a wider range of peer contexts. Legally, many adult privileges and responsibilities become possible, including voting, military service, marriage, divorce, and the ability—to those who qualify—to obtain credit, health insurance, rental accommodation, and a mortgage. Within a few years, the last adult legal rights of alcohol consumption and car rental are attained. In terms of social roles, there are transitions from high school student to college student and to worker, from casual dating to serious romantic relationships to cohabitation and to marriage, from child and sibling in the parental home to roommate and tenant and to spouse, from adolescent to single autonomous person and to parent. Many of these role transitions bring new types of relationships (e.g., tenant) whereas others are transformed (e.g., with parents, friends, romantic partners). Indeed, the density of social role changes is greater in this period than in any other period of life (Shanahan, 2000), and the same is true for geographic mobility (Arnett, 2000). Living arrangements gradually change from living with parents to living independently (Rumbaut & Komaie, 2007), primarily with same-aged peers, although there are dramatic differences in norms and patterns between countries and demographic subpopulations (Aassve, Arpino, & Billari, 2013). This change brings major declines in parental monitoring and knowledge of day-to-day lifestyles (Bachman et al., 2002), as well as dramatic increases in time spent in predominantly peer contexts (Borsari & Carey, 2001). Psychologically, there are numerous advances involving perspective taking, emotional regulation, identity, and independence (Côté, 2006; Schulenberg et al., 2003). Relatedly, there are normative neurobiological changes that take place during this time, involving, for example, transformations in the prefrontal cortex that relate to expanded executive functioning (Dahl, 2004; Spear, 2000). Finally, a particularly key transition is the movement toward self-reliance through financial independence (Arnett, 2000). Clearly, these various individual and social role transitions are interrelated (Settersten et al., 2005), and the majority are normatively experienced by many individuals regardless of whether they become full- or part-time college students after high school (Rumbaut & Komaie, 2007). The routes taken toward these changes vary greatly by many factors and have become more varied in recent generations (Bynner, 2005; Fussell & Furstenberg, 2004).

Overall, this myriad of changes may result in greater person–context match. For the individual who was psychosocially mature, vocationally focused, and supported emotionally and financially by parents, yet perhaps limited creatively or socially by a small-town high school, the freedom (p. 538) of the transition to adulthood may be particularly salutary. Indeed, the period after high school evidences population-level increases in well-being and decreases in depressive affect (Howard, Galambos, & Krahn, 2010; Schulenberg, Bryant, & O’Malley, 2004). However, for others who lack such personal and social resources, and particularly for more vulnerable populations, the decrease in structure and institutional supports (Osgood, Foster, Flanagan, & Ruth, 2005) along with the greatly intensified imperative for making one’s way in the world (Bynner, 2005) may in turn result in a markedly worse person–context match and thus contribute to negative turning points in peer relationships and substance use behaviors. It is not surprising that, in the population, diversity in life paths and the timing and content of developmental milestones increases in this age period (Evans & Baxter, 2013; Osgood, Ruth, Eccles, Jacobs, & Barber, 2005; Schulenberg et al., 2005; Settersten & Ray, 2010).

The pursuit of postsecondary or higher education is such a transformative and organizational experience that it deserves special attention. College attendance, particularly if full-time and residential, propels 17- to 19-year-olds into new and unique social environments variously focused on peers, academics, and activities (Schulenberg & Maggs, 2002). Although more self-direction is required than in high school (e.g., course selection, class attendance, laundry), college postpones the end of innumerable institutional supportive structures (e.g., accommodation with resident advisors, health centers) that are generally unavailable to those not enrolled. Most relevant to this review, students are surrounded with age mates, motivated by cultural myths extolling the college years as a time of exploration and experimentation, including with substance use, and buffered by environments that are relatively tolerant of youthful infractions (Maggs, 1997; Schulenberg & Maggs, 2002). Given these conditions, it is perhaps unsurprising that college students show high rates of heavy drinking and consequences (Hingson, Zha, & Weitzman, 2009; Perkins, 2002; Wechsler, Dowdall, Davenport, & Castillo, 1995). Degree attainment, along with the soft skills obtained in college, confers many advantages, including enhanced career opportunities and income. In addition, college degree attainment is typically associated with delayed entrance to marriage and parenthood (Settersten et al., 2005). Perhaps in part as a result, substance use patterns diverge more clearly in early adulthood between those who attended and those who did not, with a negative association between level of attained education and adult rates of smoking, alcohol problems, and marijuana and other illegal drug use and problems (Bachman et al., 1997; Muthén & Muthén, 2000).

Although substance use is typically initiated during adolescence, the transition to adulthood brings normative lifetime peaks in prevalence and intensity of use and abuse, and early adulthood is associated with normative declines for many, although not all. As individuals move out of the parental home into diverse educational, occupational, spousal, and parenting roles, there are many opportunities to select new environmental niches and develop new peer relationships, as well as greater freedom to engage in substance use. Although there is great diversity in the timing and sequence of role transitions (Evans & Baxter, 2013; Settersten & Ray, 2010), and indeed of developmental trajectories of substance use (Brook, Zhang, & Brook, 2011; Chen & Jacobson, 2012; Maggs & Schulenberg, 2005; Schulenberg et al., 1996; Staff et al., 2010), there are sufficient broad age-graded trends, including with peer and other social relationships, that seem to correspond with normative changes in substance use.

Peer Selection and Socialization in the Transition to Adulthood

As in adolescence, during the transition to adulthood—and indeed adulthood generally—individuals tend to associate and be affiliated with friends, peers, and romantic partners who are similar to them with respect to demographics, attitudes, behaviors, and lifestyles. Studies of the underlying sources of these similarities have examined selection and socialization as competing or reciprocal explanations for observed homogeneity (e.g., Bullers, Cooper, & Russell, 2001; Read, Wood, & Capone, 2005). Socialization influences are often further distinguished as direct/active (e.g., alcohol offers) versus indirect/passive (e.g., social modeling and descriptive and injunctive perceived peer norms; Graham, Marks, & Hansen, 1991; Kandel, 1985). The many developmental transitions associated with this age period furnish an abundance of opportunities for both selection and socialization processes to exert new strong effects, reflecting the potential for ontogenic discontinuity. For example, as individuals move with more autonomy into experimentation with adult roles and responsibilities, their own characteristics and self-directed decisions may shape the emergence, maintenance, and dissolution of all types of peer relationships—consistent with (p. 539) selection. At the same time, the plethora of new roles, social networks, and diverse peers that individuals may encounter provide qualitatively and quantitatively more varied opportunities for peers to influence the individual with new ideas, values, and lifestyles.

Whether peers and their influences on substance use are likely to lessen or intensify following the end of high school is debatable. One might conjecture that peers would play a more important role in the transition to adulthood than in adolescence due to a variety of factors: cultural expectations that this time of life is characterized by peer-shared experimentation (Arnett, 2000; Maggs, 1997); moving away from the parental home and parents’ monitoring and guidance (White, Fleming, Kim, & Catalano, 2008); living with same-aged roommates (Duncan, Boisjoly, Kremer, Levy, & Eccles, 2005); the ability to smoke and later drink legally and in public, with increased opportunities to do so at major and normative social venues, such as parties and bars (Harford, Wechsler, & Seibring, 2002); the increasing intensity of romantic relationships, including the likelihood of sex (in casual or serious relationships) and cohabitation (Lefkowitz & Gillen, 2005); and individuals’ attempts to fit in and progress in novel social environments that may be conducive to substance use, including college and new careers (Schulenberg & Maggs, 2002). Conversely, one might speculate that peers and their influence would decline in the transition to adulthood for multiple reasons: increased emotional maturity and a sense of self and identity (Côté, 2006); a decline, relative to middle and high school, in the importance of narrowly defined adolescent popularity as a determinant of social success—although some college environments and activities may extend this; more opportunities for self-direction in terms of major institutional connections (e.g., which school to attend; which job to apply for), activities, and time use (although these vary greatly between people; Bynner, 2005); more established behavioral patterns with increased age, leading to greater stability of substance use behavior (Labouvie, 1996); and an increase in normative anti–substance use pressures, including societal norms against irresponsible drug use and the increased pressures of succeeding in adult social roles, such as being a responsible worker, spouse, and parent (Bachman et al., 1997).

A large portion of the empirical work on peer influence has focused on adolescents and college students, such that the study of peer influences on substance use among the general population of young adults has been relatively neglected (for notable exceptions see, e.g., Andrews et al., 2002; Bullers et al., 2001; Quinn & Fromme, 2011; White, Labouvie, & Papadaratsakis, 2005; White et al., 2008). (Influences of marital, parental, and work transitions on substance use have received more attention but are beyond the scope of this chapter.) Although many of the major developmental transitions are experienced by those who do and do not attend college, important differences between these two groups caution against uncritically generalizing results from students to the population at large. Such group differences occur in the timing, sequence, and success of attaining these changes; in the social contexts they encounter; in the advantages and supports they experience; and in the substance use patterns of young adults (Andrews et al., 2002).

Peer Influences in the Transition to Adulthood: General Population Studies

Community and national surveys examining the combined impact of peer selection and socialization as influences on substance use after high school, similar to findings in adolescence, have shown both processes to continue to play important roles, although evidence for selection appears stronger. For example, White et al. (2008) followed four groups of individuals across the transition out of high school: those who did and did not leave the parental home and those who did and did not go to college. Each group showed evidence of selection and socialization with respect to alcohol use, with those reporting more alcohol use in senior year of high school increasing their self-reported pro-alcohol influences the next fall, and those with more pro-alcohol influences reporting greater increases by the following spring. In a longitudinal study of same- and opposite-sex friends’ influences, focusing on modal ages 21–24, Andrews et al. (2002) found evidence of primarily selection effects for alcohol and marijuana use and primarily socialization effects for cigarette use and binge drinking. Similarly, Bullers et al. (2001) observed reciprocal influences in an adult sample, but effect sizes were larger for selection. Self-direction (or selection) is also evident in maturing out of cigarette, alcohol, and illegal drug use, with early adults who married, remained married, and became parents during their 20s reducing their use more than others, in part through differential association with similar behavioral norms and actions (Labouvie, 1996). These findings are consistent with reciprocal (p. 540) determinism, as described by Bandura (1969), and are not surprising, given the nature of the transition to adulthood and the ability for individuals to be active participants in constructing their social environments (Maggs, 1997) rather than passive victims of social pressures (Graham et al., 1991).

Empirical Research Focused on College Students

The College Environment

The transition to college has been described as ideal for studying peer influences, particularly among individuals who leave their family homes and peer environments to build new social networks on campus (Borsari & Carey, 2001). This developmental transition may be especially important for substance use, given high prevalence and dramatic day-to-day variability of alcohol use among college students and abundant opportunities in most collegiate environments to engage in alcohol-based social activities (Maggs, Williams, & Lee, 2011; Schulenberg & Maggs, 2002).

Social Aspects of the College Environment

One study that assessed alcohol use, offers to use alcohol, social modeling of use, and perceived norms the summer preceding college entrance and again during the spring of college students’ second year found evidence consistent with predominant selection effects (Read et al., 2005). Higher levels of alcohol use and alcohol problems prior to college were consistently associated with selecting into environments where there were more offers to use alcohol and a greater level of social modeling of alcohol use, whereas there was weaker support or no support for the precollege offers, modeling, and norms to influence later alcohol use (Read et al., 2005). However, this may be an incomplete test of reciprocal effects because this study does not capture the socialization influences during the first year of college. The precollege influences would be anticipated to desist because the college environment provides an entirely new context and socializing group.

As reviewed by Borsari and Carey (2001), peers provide both direct and indirect influences on substance use. Direct influences include active attempts to get each other drunk, offering each other drugs, and encouraging use through taunting or pressure to participate in drinking games. According to their review, findings from a limited amount of qualitative research suggest that direct offers are common, although women and individuals who are socially secure tend to refuse more often. Indirect influences include modeling of and social norms regarding appropriate and acceptable behavior. Increased exposure to modeled heavy drinking, especially by individuals who are sociable or in larger confederate groups in experimental designs, increases consumption. In addition, descriptive norms (i.e., perception of peers’ behavior) and injunctive norms (i.e., perception of peer approval of behavior) have been shown to be important predictors of behavior such as alcohol use (e.g., Baer, 2002; Baer, Stacy, & Larimer, 1991; Borsari & Carey, 2001; 2003; Lewis & Neighbors, 2004). For a review on the use of norms in alcohol intervention programs, see Prentice (2008).

Structural and Administrative Effects on Peer Influence

Early social influence work among college students focused on the architectural effects of dormitory buildings, concluding that the functional distance between one’s room and the rooms of other students has an effect on the social relationships that develop (Case, 1981; Festinger, Schachter, & Back, 1950). Research has also taken advantage of the natural experiment allowed by random roommate assignment among first-year college students, demonstrating that for male students who had engaged in binge drinking in high school, the drinking history of the new roommate was pivotal in their continued drinking (Duncan et al., 2005). That is, binge drinkers randomly paired with other binge drinkers (reflecting a likely continued person–context match) continued and escalated their heavy drinking much more than binge drinkers paired with non–binge drinkers (reflecting a likely mismatch).

Fraternity and Sorority Affiliation

Fraternities and sororities provide an interesting lens into the influences of selection and socialization surrounding substance use. Greek members evidence heavier alcohol use and consequences than do non-Greek members (Alva, 1998; Mallett et al., 2013), particularly among those living in fraternity-/sorority-sponsored housing (Wechsler et al., 1995). Greek members also report higher use rates of cigarettes, marijuana, and ecstasy (McCabe et al., 2005; Mohler-Kuo, Lee, & Wechsler, 2003; Yacoubian, 2003), although rates of these substances are much lower than for alcohol. Many Greek environments effectively congregate individuals prone to and interested in alcohol use, provide access to alcohol and parties, and tolerate or encourage use (p. 541) and heavy use (Park, Sher, Wood, & Krull, 2009). Thus, fraternities and sororities represent a major risk factor facilitating heavy drinking and serious negative consequences. This assertion is consistent with a process of peer influence.

Debate about the effects of fraternity and sorority membership on heavy drinking is centered on at least two major issues. First, self-selection into and out of Greek affiliations represents a plausible rival hypothesis that may explain at least a portion of purported socialization effects. Consistent with reciprocal determinism, selection effects are signaled by findings that Greek-involved college students are more likely to be white (conferring higher risk for problem drinking in college; Wechsler et al., 1995); have greater precollege extraversion, sensation seeking, and motivations to party and attend sporting events during college (Kahler, Read, Wood, & Palfai, 2003; Park, Sher, & Krull, 2008); and report greater precollege alcohol use and problems (Capone, Wood, Borsari, & Laird, 2007; McCabe et al., 2005; Park et al., 2008) when compared to non–Greek-involved students. Indicating the effects of socialization, Greek affiliation during college is associated with greater alcohol availability (Park et al., 2008), reported increases in alcohol (Capone et al., 2007) and marijuana use (McCabe et al., 2005), and decreases in binge drinking after transitioning out of Greek organizations (McCabe et al., 2005; Park et al., 2008). Links between substance use and Greek affiliation are most studied, and most apparent, for alcohol and, to a lesser extent, marijuana. For example, changes in smoking and illicit drug use other than marijuana did not differ by Greek status, perhaps due to low prevalence of both behaviors among college students (McCabe et al., 2005; Park et al., 2008). Taken together, these results clearly show that selection into different environments may in turn provide differential contexts for socialization (Kahler et al., 2003). Presumably, individuals who seek out substance-using environments may be more susceptible to active and passive pro-substance use influences once they are in these settings. Finally, only some of the just-mentioned studies have observed gender differences in these processes. When present, it would appear that men may be more subject to socialization or influence effects than are women (McCabe et al., 2005; Read, Wood, Davidoff, McLacken, & Campbell, 2002).

A second issue of debate is whether Greek members maintain their heavy drinking and problems with alcohol in adulthood, after leaving the college environment. In a longitudinal study of college to adult drinking trajectories, male and female Greek members evidenced large differences in heavy drinking during college, but this effect appeared to be limited to the college years because they showed no differences 3 years (Sher, Bartholow, & Nanda, 2001) and 11 years later (Bartholow et al., 2003). These authors concluded that the convergence of heavy drinking trajectory slopes after college points to the impact of the immediate environment, citing social control theory and social learning theory. In social control theory (e.g., Shoemaker, 1990), environmental and structural influences provide explanations for the normative increases in emerging adult alcohol use, whereas social learning theory (e.g., Bandura, 1969) identifies proximal social models and reward structures as an explanation for normative decreases in early adulthood as adult social roles are initiated (see also Bachman et al., 1997; 2002).


Clearly, across adolescence and the transition to adulthood, substance use is embedded within peer relationships, characteristics, and processes. In just about any relevant study, peer substance use has been found to be one of the strongest contemporaneous predictors of adolescent substance use. In a recent cross-sectional analysis of eighth- and tenth-grade data from the national Monitoring the Future study, we found that the proportion of friends who get drunk to be the single strongest predictor of binge drinking (among eighteen demographic and psychosocial predictors); indeed, it was a stronger predictor than cigarette use or marijuana use (Patrick & Schulenberg, 2010). Of course, the central issue in this chapter is the causal direction between one’s drug use and peers’ use and, in particular, how it unfolds developmentally. As we have seen here, the twin processes of selection and socialization, coupled with an appreciation for the developmental tasks and transitions of adolescence and early adulthood, provide a framework for understanding how substance use and peers are interconnected over time. In this final section, we consider limitations of the previous research and offer some future directions before we provide concluding comments.

Limitations of Previous Research

Several authors have pointed to important methodological considerations that may limit the ability of studies to detect selection and/or socialization effects. Specifically, measurement limitations and (p. 542) biases may overestimate the effects of peer socialization on substance use. First, cross-sectional studies confound selection and socialization effects and tend to overestimate the influences of both (Bullers et al., 2001). Second, heavy reliance on self-report measures introduces reporting biases such as reflection and attribution when reporting about the behavior of one’s peers (Kandel, 1996). An additional methodological confound occurs when studies that find support for socialization fail to control for initial selection of substance-using peers and therefore overestimate the effects of peer influence (Bauman & Ennett, 1996). Peers are often not directly assessed in studies that assess their influence on behavior. In addition, most studies implicitly assume that the respondents are influenced by their social networks, rather than vice versa (Bullers et al., 2001), although clearly individuals both influence and are influenced by their peers. Finally, the effects of parents, siblings, and others on an individual’s substance use and on his or her choice of friends are generally not measured or accounted for.

Future Directions

Despite the amount of research attention that has been paid to peer relationships, their complexity in the lives of individuals and their influences across the lifespan require renewed and ongoing research attention. There are several key areas for future research. First, it is important to distinguish the influences of best friends, peer groups, and social crowds (Kobus, 2003). Romantic relationships also deserve more serious research attention (Furman & Simon, 2008). As reviewed earlier, different types of peer relationships likely have different selection criteria and variable strength of influence in the lives of adolescents.

Second, systematic investigations of variations in peer relationships by major moderators such as gender, socioeconomic status, culture, and race/ethnicity are lacking. Studies on racial and ethnic differences in peer influences on substance use are virtually nonexistent (Borsari & Carey, 2001). In addition, some researchers have contended that the relative role of selection and socialization may vary by culture. Chatard and Selimbegovic (2007), for example, suggest that individual self-selection factors may play a larger role in individualistic cultures (in which the majority of research has been conducted), whereas socialization effects may provide a stronger effect in collectivist cultures.

Third, specific substances and type of substance use behaviors (i.e., initiation of use, rate of growth of use, overall frequency of use) require additional study. It has been shown that peer processes relate differentially and specifically to various substances and at different stages of use (e.g., initiation; Kandel, 1985), and this should be acknowledged in peer influence models.

Fourth, longitudinal research is needed to examine the role of peers in individuals’ lives from late childhood through adulthood. As described earlier, peer associations change over time and with developmental transitions. Just as individuals grow and change, so do peer groups and relationships. Very little is known, for example, about how peer influences change when one member of a group initiates or desists substance use (Kobus, 2003). Following peer groups over time using methods such as social network analysis may be a fruitful area of future research.

Finally, a better understanding of both macro- and microcontexts is needed. The influence of neighborhoods, schools, and communities may be particularly important for setting the stage for peer influence. In some areas, for example, the presence of gangs or violent peer groups may dominate. The effects of these types of contextual differences need to be better understood. In addition, the microcontext of peer interactions, including how adolescents negotiate new friendship interactions and encourage or discourage their peers to use substances in real time and in different contexts (e.g., parties, clubs), will further illuminate the processes of selection and socialization. Specifically, ethnographic analysis of buying a round of drinks and engaging in drinking games would provide interesting information about peer influences (Borsari & Carey, 2001). Understanding microcontexts also requires an acknowledgment of reciprocity in friendships (Prinstein & Dodge, 2008), which includes the potential for friends to mutually influence one another, rather than a unidirectional model whereby a participant is assumed to be influenced by peers without exerting any influence back.

Implications: “I Get High with a Little Help from My Friends”

Increased risk taking during adolescence is normative, along with intensified relationships with peers. Although not a recommended route, both risk taking and peer bonding can sometimes be accomplished through substance use (Schulenberg & Maggs, 2002). Indeed, adolescents typically report that a primary reason for using drugs is to have a good time with their friends (Johnston & (p. 543) O’Malley, 1986; Patrick et al., 2011a; Patrick et al., 2011b; Patrick & Schulenberg, 2011). According to Chassin et al. (1999), risk taking and even deviance can serve “constructive” as well as “destructive” functions in health and development (see also Jessor & Jessor, 1977; Spear, 2000). As Maggs (1997) demonstrates, alcohol use during the transition to college may help to achieve valued social goals, such as making new friends, although at the same time it may threaten safety and short- and long-term health and well-being. Thus, substance use can sometimes be used to help negotiate various social and identity transitions, and at other times substance use can impede successful negotiation of such transitions.

In a multinational study of thirty-one European and North American countries, Kuntshe et al. (2009) found that the decline in marijuana use among 15-year-olds between 2002 and 2006 was associated with a decline in the frequency of evenings out with friends. Although some may assume a causal link of evenings with friends on substance use, imposing limits on free time with friends would likely have unintended consequences. As we have discussed in this chapter, essential tasks of adolescence involve exploring and forming friendships, having bonding experiences, and finding a safe haven with peers away from adult supervision. Identity quests demand this time. Thus, rather than attempting to limit time with friends, a more complicated but likely more successful approach to intervention would be to help young people find bonding experiences that do not involve drug use (Caldwell & Smith, 2006; Schulenberg & O’Malley, 2009).

In this chapter, we have placed the peer–drug use link within a broader developmental perspective, highlighting the twin processes of selection and socialization. The theoretical and practical implications of gaining insight into the links between peers and substance use are sizeable, particularly when considering how these links change across the many transitions of adolescence and early adulthood. As more is understood about this rich set of relationships, we slowly disentangle the complexities that form the foundation of social development and substance use.

Authors’ Note

Work on this chapter was funded in part by support from the National Institute on Drug Abuse (R01DA001411, R01DA016575, and R21DA031356). The content here is solely the responsibility of the authors and does not necessarily represent the official views of the sponsors.


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