Exploring Cannabis and Alcohol Co-Use in Adolescents: A Narrative Review of the Evidence

Objective: Amidst the evolving policy surrounding cannabis legalization in the United States, cannabis use is becoming increasingly prevalent as perceptions of harm decrease, particularly among adolescents. Cannabis and alcohol are commonly used by adolescents and are often used together. However, developmental research has historically taken a "single substance" approach to examine the association of substance use and adolescent brain and behavior rather than examining co-(or poly-substance) use of multiple substances, such as cannabis and alcohol. Thus, the acute effects of cannabis and alcohol, and the impact of co-use of cannabis and alcohol on the adolescent brain, cognitive function and subsequent psychosocial outcomes remains understudied. This narrative review aims to examine the effects of cannabis and alcohol on adolescents across a number of behavioral and neurobiological outcomes. Methods: The PubMed and Google Scholar databases were searched for the last 10 years to identify articles reporting on acute effects of cannabis and alcohol administration, and the effects of cannabis and alcohol on neuropsychological, neurodevelopmental, neural (e.g., structural and functional neuroimaging), and psychosocial outcomes in adolescents. When adolescent data were not available, adult studies were included as support for potential areas of future direction in adolescent work. Results: Current studies of the impact of cannabis and alcohol on adolescent brain and behavior have yielded a complicated pattern. Some suggest that the use of cannabis in addition to alcohol during adolescence may have a "protective" effect, yielding neuropsychological and structural brain outcomes that are better than those for adolescents who use only alcohol. However, other adolescent studies suggest that cannabis and alcohol co-use is associated with negative health and social outcomes such as poorer academic performance and impaired driving. Conclusion: Variation in study methodologies, policy-level limitations and our limited understanding of the developmental neurobiological effects of cannabis preclude the straightforward interpretation of the existing data on adolescent cannabis and alcohol use. Further research on this topic is requisite to inform the development of effective intervention and prevention programs for adolescent substance users, which hinge on a more comprehensive understanding of how cannabis-and its intersection with alcohol-impacts the developing brain and behavior.