BACKGROUND: This study compared young adults with and without a medical marijuana (MM) recommendation from a provider ("MM card") on their developmental trajectories of frequent marijuana use and marijuana-related problems in young adulthood. METHODS: The analytic sample consists of young adult past month marijuana users (N = 671) who were part of a larger, diverse, and predominantly California cohort. Analyses are based on data from seven surveys completed from ages 13-19. RESULTS: At age 19, 28% of participants reported having an MM card to legally purchase marijuana from an MM dispensary. A multiple group latent growth model indicated that young adults who had an MM card showed steeper increases in frequent marijuana use (i.e., 20-30 days of use in the past month) from ages 13-19 compared to young adults who did not have an MM card. Logistic regression models that matched MM cardholders and non-MM cardholders on individual sociodemographic characteristics found that MM cardholders were more likely to report marijuana negative consequences, selling marijuana/hashish, and driving under the influence of marijuana in the past year. In addition, MM cardholders were more likely to have tried cutting down or quitting in the past 3-months. CONCLUSIONS: Among young adult marijuana users, those with an MM card had a higher risk profile for marijuana use and related problems compared to those without an MM card. Given expanding state legalization of MM, this issue warrants further attention.
