Cannabis and Alcohol Use Trajectories: Mixed-Methods Retrospective Study of Interconnectedness

In-depth understanding of how patterns of cannabis and alcohol co-use and substitution evolve among young adults as they transition into adulthood is limited. In 2021-2022, 25-33-year-old participants ( n = 39) originally recruited in Los Angeles were interviewed qualitatively where they reflected on graphs charting seven years of quantitative data on cannabis and alcohol use and the relationahip between the two substances. Three patterns of intersections between alcohol and cannabis use emerged: substitution, enhancement, and counteraction amongst four trajectory groups: High cannabis/Low alcohol n = 19, High cannabis/High alcohol n = 9, Low cannabis/Low alcohol n = 6, Low cannabis/High alcohol n = 5. No combination between alcohol and cannabis was more common than any of the three patterns. Cannabis use remained high for a majority. A small number of participants struggled with problematic alcohol use across the study period. Consistent with maturational trends, a harm reduction approach to cannabis and alcohol use (i.e., substitution, counteraction) persisted, while recreationally oriented co-use (i.e., enhancement) lessened over time.