Supporters of recreational marijuana legalization often point to youth prevalence rates as evidence that legalization has not negatively impacted youth. But simply looking at whether marijuana use has increased or decreased does not tell the whole story. Changes in youth use following legalization and the COVID-19 pandemic demonstrate why the timing and measures used to evaluate legalization are important. For example, what happens when we look beyond prevalence and examine problematic use and addiction among youth?
A new study published in Addiction examined this question by looking beyond whether youth reported using marijuana and instead analyzing diagnoses of cannabis use disorder (CUD). CUD is a clinical diagnosis characterized by a problematic pattern of marijuana use that results in significant impairment or distress.
In this study, researchers examined electronic health records from 637,461 adolescents ages 13 to 17 enrolled in Kaiser Permanente Northern California (KPNC) between January 2014 and February 2020. KPNC routinely provides adolescent preventive care that includes substance use screening, giving researchers an opportunity to examine changes in newly diagnosed CUD over time.
Researchers examined monthly rates of newly diagnosed CUD in relation to two major policy changes in California:
- November 9, 2016: California passed recreational cannabis legalization. The law legalized adult possession and home cultivation and reduced penalties for cannabis possession among individuals under age 21.
- January 1, 2018: Legal recreational retail cannabis sales began.
Because problematic marijuana use and symptoms of CUD may take time to develop and result in a clinical diagnosis, researchers incorporated a six-month lag following each policy change. Researchers also ended the study period in February 2020, avoiding the major disruptions to health care and adolescents' daily lives caused by the COVID-19 pandemic.
Researchers identified 8,804 new CUD diagnoses during the study period. Before recreational legalization passed, new CUD diagnoses among adolescents declined by approximately 5% per year. After legalization passed, that trajectory changed. Researchers found a statistically significant upward change in the trend of new CUD diagnoses six months after passage.
Six months after recreational retail sales were implemented, researchers found a statistically significant downward change in the slope. CUD incidence continued to increase, although the subsequent increasing trend was no longer statistically significant. The researchers concluded that trends in youth CUD rates appeared to increase following recreational marijuana legalization, with increasing rates persisting through retail implementation and three years after passage.
These findings raise an important issue for how we measure the public health impact of legalization. Simply asking whether the percentage of youth who use marijuana has changed may overlook important shifts in patterns of use and the consequences associated with that use. This is particularly important when considering cannabis use disorder. Adolescence is a critical period for prevention, and delaying substance use initiation can help reduce the risks associated with early and problematic use.
Another important consideration is that when recreational marijuana legalization passed in California, penalties for marijuana possession among individuals under age 21 were also reduced. Legalization changes more than the legal status of a substance. It may affect the broader environment in which youth develop beliefs about marijuana, including perceptions of risk and social acceptance. Commercial legal markets can also include greater product diversity, higher-potency products, and marijuana marketing.
These findings reinforce a critical prevention message: Legal does not mean safe, especially for our youth.
Evaluations of marijuana policy should examine not only how many use marijuana, but also how often they use, how patterns of use change over time, and how many develop cannabis use disorder or experience other adverse health outcomes. A comprehensive assessment of legalization requires looking beyond prevalence to understand the full picture.
Source
Padon, A. A., Cortez, C. A., Alexeeff, S. E., Slama, N. E., Pacula, R. L., Silver, L. D., Sterling, S. A., Campbell, C. I., Satre, D. D., Does, M. B & Young-Wolff, K. C. (2026). Adolescent cannabis use disorder following recreational cannabis legalization in California, USA: A population-based interrupted time series study. Addiction. https://doi.org/10.1111/add.70597
