Analyzing data from over 1 million high school students across 46 states from 1991-2015, researchers found no evidence that medical marijuana laws or dispensaries increased adolescent marijuana use.
Policymakers, public health officials, and parents concerned about legalization effects on youth.
No increase in teen marijuana use after medical marijuana laws in 46 states
What the researchers found
States with enacted medical marijuana laws actually showed slightly lower adjusted odds of adolescent past-30-day marijuana use (OR=0.94, 95% CI: 0.89-0.99). No increase in heavy use (20+ days/month) was detected. Dispensary provisions were also not associated with higher adolescent use.
Why it matters
A primary concern about marijuana legalization is increased teen use. This study, one of the largest to examine the question, found no evidence for that concern across nearly 25 years of data, providing important evidence for the policy debate.
The numbers in context
1,091,723 students, 46 states, 1991-2015. MML states: OR=0.94 (95% CI: 0.89-0.99) for any past-30-day use. No significant effect on heavy use (20+ days). Dispensary provisions also not associated with increased use.
How the study worked
Natural-experimental design using state Youth Risk Behavior Survey (YRBS) data from 1,091,723 students in grades 9-12 across 46 states (1991-2015). Difference-in-difference estimates compared states before and after MML enactment. Multivariable logistic regression adjusted for state and year effects and student demographics.
What this study cannot tell us
YRBS data is self-reported. Does not capture recreational legalization effects (only medical). Cannot account for all state-level confounders. 1991-2015 timeframe may not reflect more recent policy environments.
How to read the evidence
Very large sample with quasi-experimental design across 25 years and 46 states. Strong for policy evaluation.
When this study was published
2021 study analyzing YRBS data from 1991-2015.
The bigger picture
These findings are consistent with a growing body of research suggesting that medical marijuana legalization does not measurably increase teen use. The slight negative association may reflect that states willing to enact MMLs also invest in youth prevention programs, though the study cannot confirm this.
Questions still open
- Does recreational legalization (vs. medical) show different effects on teen use? What mediates the slightly protective association? Would longer follow-up periods change the findings?
Common questions
Did medical marijuana laws increase teen marijuana use?
What about marijuana dispensaries?
Read the original research
Medical marijuana laws (MMLs) and dispensary provisions not associated with higher odds of adolescent marijuana or heavy marijuana use: A 46 State Analysis, 1991-2015.
Substance abuse, 42(4), 471-475
Citation
Johnson, Julie K; Johnson, Renee M; Hodgkin, Dominic; Jones, Abenaa A; Kritikos, Alexandra; Doonan, Samantha M; Harris, Sion K. (2021). Medical marijuana laws (MMLs) and dispensary provisions not associated with higher odds of adolescent marijuana or heavy marijuana use: A 46 State Analysis, 1991-2015.. Substance abuse, 42(4), 471-475. https://doi.org/10.1080/08897077.2021.1900986