Medical marijuana laws were not associated with increased teen marijuana use across 46 states
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.
Quick Facts
What This Study 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.
Key Numbers
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 They Did This
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.
Why This Research 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 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.
What This Study Doesn't 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.
Questions This Raises
- ?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?
Trust & Context
- Key Stat:
- No increase in teen marijuana use after medical marijuana laws in 46 states
- Evidence Grade:
- Very large sample with quasi-experimental design across 25 years and 46 states. Strong for policy evaluation.
- Study Age:
- 2021 study analyzing YRBS data from 1991-2015.
- Original Title:
- 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.
- Published In:
- Substance abuse, 42(4), 471-475 (2021)
- Authors:
- Johnson, Julie K(3), Johnson, Renee M, Hodgkin, Dominic, Jones, Abenaa A, Kritikos, Alexandra, Doonan, Samantha M, Harris, Sion K
- Database ID:
- RTHC-03227
Evidence Hierarchy
Follows a group of people over time to track how outcomes develop.
What do these levels mean? →Frequently Asked Questions
Did medical marijuana laws increase teen marijuana use?
No. States with medical marijuana laws showed slightly lower odds of adolescent use (OR=0.94), and no increase in heavy use was detected across 46 states over 25 years.
What about marijuana dispensaries?
Operational dispensaries were also not associated with higher adolescent use, countering concerns that physical access points would increase teen exposure.
Read More on RethinkTHC
Cite This Study
https://rethinkthc.com/research/RTHC-03227APA
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
MLA
Johnson, Julie K, et al. "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, 2021. https://doi.org/10.1080/08897077.2021.1900986
RethinkTHC
RethinkTHC Research Database. "Medical marijuana laws (MMLs) and dispensary provisions not ..." RTHC-03227. Retrieved from https://rethinkthc.com/research/johnson-2021-medical-marijuana-laws-mmls
Access the Original Study
Study data sourced from PubMed, a service of the U.S. National Library of Medicine, National Institutes of Health.
This study breakdown was produced by the RethinkTHC research team. We analyze and report published research findings without making health recommendations. All interpretations are based solely on the published abstract and study data.