After Massachusetts legalized recreational cannabis sales, THC-positive rates among adolescent psychiatric ER patients surged from 5% to 17%, and cannabis use disorders jumped from 3% to 12% — a 4.6-fold increase.
Child psychiatrists, adolescent mental health providers, policymakers designing legalization safeguards, and parents of teens with psychiatric conditions.
What the researchers found
THC positivity increased from 32.4% to 36.3% overall (p<.001). Adolescents (12-17) had the largest increase: from 5% to 17.3% (AOR=4.32). Only adolescents showed a significant increase in cannabis use disorders: from 3.2% to 12.1% (AOR=4.63). Adults aged 26-49 showed a modest THC positivity increase (AOR=1.24).
Why it matters
Psychiatric patients are among the most vulnerable to cannabis harms, and adolescents with psychiatric conditions are especially at risk. This study provides direct evidence that cannabis commercialization disproportionately affects the youngest, most vulnerable psychiatric patients.
The numbers in context
7,350 presentations. Overall THC+: 32.4% → 36.3%. Adolescents: THC+ 5% → 17.3% (AOR=4.32). Adolescent CUD: 3.2% → 12.1% (AOR=4.63). Adults 26-49: THC+ 37.7% → 42.5% (AOR=1.24). Adults 18-25 and 50-70: no significant changes.
How the study worked
Cross-sectional analysis of 7,350 unique presentations to a psychiatric emergency service at a tertiary hospital in Massachusetts. Compared pre-commercialization (Jan 2017-Nov 2018) to post-commercialization (Nov 2018-Dec 2019) periods. Logistic regressions controlled for sex, race, and ethnicity across age groups.
What this study cannot tell us
Single hospital, single state. Pre/post comparison without control group. Short post-commercialization period (13 months). THC positivity doesn't indicate cannabis caused the ER visit. Psychiatric ER patients are a specific, high-risk population.
How to read the evidence
Single-center pre-post study with objective THC testing — provides compelling evidence of temporal association though cannot prove causation.
When this study was published
Published in 2026, examining the early impact of Massachusetts cannabis commercialization (2018).
The bigger picture
The 4.6-fold increase in adolescent cannabis disorders in psychiatric ER patients is alarming. These are already high-risk youth, and increased cannabis exposure may worsen psychiatric outcomes. This has direct implications for how legalization is implemented and what protections are needed for vulnerable populations.
Questions still open
- What safeguards could protect psychiatric adolescents during legalization? Are there longer-term psychiatric consequences? Do other states show similar patterns?
Common questions
Does cannabis legalization affect teens with mental health issues?
Why are psychiatric teens more vulnerable?
Read the original research
Effects of Legalizing Recreational Cannabis Sales on Cannabis Use and Cannabis-Related Disorder Among Presentations to a Psychiatric Emergency Service.
American journal of preventive medicine, 70(1), 108142
Citation
Foo, Cheryl Y S; Potter, Kevin; Wright, Abigail C; Evins, A Eden; Donovan, Abigail L; Levy, Sharon; Mueser, Kim T; Cather, Corinne. (2026). Effects of Legalizing Recreational Cannabis Sales on Cannabis Use and Cannabis-Related Disorder Among Presentations to a Psychiatric Emergency Service.. American journal of preventive medicine, 70(1), 108142. https://doi.org/10.1016/j.amepre.2025.108142