Sabrina Mörkl, Mary I. Butler, Franziska Cichini, John F. Cryan, and Timothy G. Dinan
For centuries, individuals have consumed probiotics as a means of improving quality of life and preventing disease. The gut microbiota refers to the collection of microorganisms residing within the gut. Psychiatric disorders show profound alterations of gut microbiota composition along with a lack of bacterial diversity. Specific subtypes of probiotics and prebiotics (fibers that promote the growth of beneficial bacteria) are referred to as psychobiotics, which impact the gut-brain axis and result in modifications of mood, anxiety, and cognitive function. It is essential for psychiatrists to improve their understanding of psychobiotic mechanisms and the evidence that supports their use in practice. In recent years, interventional studies have assessed the effects of psychobiotics for several symptom clusters, including depression and anxiety. However, some significant determinants, including duration of treatment, dosage of psychobiotics, and interactions with concomitant therapies, deserve more detailed investigation, and specific treatment guidelines for psychobiotics have not yet been established. The capacity of pre- and probiotics to modify psychological symptoms, while significant, is likely to be modest. In addition, this psychobiotic ability varies among probiotic strains—not all psychobiotics are right for all diseases. As psychobiotics are generally considered safe, this may justify their use as an add-on-therapy for some psychiatric indications. This chapter reviews the role of psychobiotics for mental health, their definition, their characteristics, and their mechanisms of action. Against the background of recent research, the chapter outlines a “psychobiotic prescription” to justify a condition-specific rationale for the use of psychobiotics based on recommendations in the current literature.