Oakland, CA—New diagnoses of cannabis use disorder (CUD) among adolescents in Northern California began climbing after recreational cannabis was legalized in California in 2016, reversing a steady decline in the three years prior, according to a new study published in the journal Addiction. The researchers say their findings call for disorder-level outcomes to be tracked alongside standard measures of use prevalence and frequency when evaluating the public health effects of cannabis legalization.
"Most surveys of adolescent cannabis use tell us how many teens have tried cannabis, but don't tell us how many are developing a disorder that brings them into clinical care," said Alisa Padon, Ph.D., the lead author on the study and research director at Getting it Right from the Start, a project of the Public Health Institute. "The public health goal is to reduce the harms caused by cannabis use and we cannot reduce what we do not measure."
National surveys have shown that overall rates of teen cannabis use have stayed relatively flat for two decades. Those figures are often cited as evidence that legalization has not affected young people. However, research shows that the risk of developing CUD, a complex condition that involves a problematic pattern of cannabis use, rises sharply with more frequent use and with earlier age of first use. By tracking diagnoses over time rather than at a single point, the study makes visible a shift toward frequent and problematic use that national survey figures of cannabis use alone do not reveal.
Researchers analyzed six years of electronic health record data from 637,000 adolescents receiving care at Kaiser Permanente Northern California. The periods studied were before the 2016 ballot measure passed, between passage and implementation, and after recreational retail sales began, through early 2020. Using an interrupted time series design, they tested whether trends in new CUD diagnoses shifted across those policy periods. The cohort had a mean age of 14.1 years at baseline and was 50.9% male, 33.6% non-Hispanic White, 29.6% Hispanic, 17.1% non-Hispanic Asian, 8.0% non-Hispanic Black and 11.5% multiple, other, or unknown race and ethnicity. Average enrollment lasted 27.4 months, and the demographic makeup of the cohort was similar across time periods.
Key findings:
- CUD diagnoses fell about 6% a year before the 2016 vote and rose about 8% a year after, a reversal of the prior trend.
- The upward trend continued after recreational retail sales began.
- By early 2020, more than three years after passage, diagnoses were back to their 2014 level.
- Among the 637,461 adolescents studied, 8,804 were newly diagnosed with CUD over the six years.
The shift in CUD diagnosis began at passage of legalization rather than at the opening of retail stores, which the authors say may reflect changes in the broader legal and social environment around the vote. Passage reduced criminal penalties for cannabis offenses for juveniles, potentially altering how teens weighed the consequences of use. It may also have acted as a normative signal that cannabis is socially acceptable or low-risk, a message amplified by cannabis-related promotion around the 2016 ballot campaign. In addition, as the retail market matured, youth-appealing advertising, product variety and higher-potency THC products expanded, factors that can increase the likelihood of progression to frequent use.
"The new study shows that cannabis laws are tied to changes in young people's rates of cannabis use disorder," said senior author Kelly Young-Wolff, PhD, MPH, a research scientist at the Kaiser Permanente Division of Research. "As potency has risen, it's more important than ever that families understand this is a product that can be addictive and, for some kids, requires real medical care."
The pattern of CUD diagnosis the research team found echoes a companion study on adolescent self-reported cannabis use they published earlier this year in JAMA Network Open. The study found use was falling before California's legalization, began climbing after the law passed but before retail stores opened and continued rising to a high of 9.5% in early 2020, when the COVID-19 pandemic began. In 2024 adolescent use was at 6.5%—near where it stood just before legalization.
The new study has several limitations. The study population were adolescents insured through and seeking care at Kaiser Permanente Northern California, so results may not apply to teens in Southern California, other states or those who are uninsured. Because Proposition 64 took effect statewide, there was no comparison group of unexposed adolescents, and the single-group design cannot rule out unmeasured trends over the same years, including broader shifts in adolescent mental health, screening practices or health care use. The analysis was not preregistered, and the study period ended before the COVID-19 pandemic, limiting conclusions about longer-term trends.
Study:
Padon, AA, Cortez, CA, Alexeeff, SE, Slama, NE, Liccardo Pacula, R, Silver, LD, Sterling SA, Campbell CI, Satre DD, Does MB, Young-Wolff KC. Adolescent Cannabis Use Disorder Following Recreational Cannabis Legalization in California, USA: A Population-Based Interrupted Time Series Study. Addiction. 2026. https://onlinelibrary.wiley.com/doi/abs/10.1111/add.70597
