An evidence and gap map of 447 studies on cannabis liberalization found most research focused on cannabis use as an outcome, while more than half of the 113 outcomes identified were addressed by three or fewer studies, revealing massive evidence gaps.
Cannabis policy researchers, research funders, legislators, public health agencies.
Over half of 113 cannabis policy outcomes had 3 or fewer studies
What the researchers found
The EGM includes 447 studies (438 primary, 9 systematic reviews). Most research is from the US. Research concentrates on medical and recreational cannabis laws; industrial hemp, CBD, and decriminalization laws are rarely studied. Cannabis use was the most frequently studied outcome. Over half of 113 documented outcomes had 3 or fewer studies. Only 7 systematic reviews existed, and 5 were rated minimal quality.
Why it matters
With 21+ US states having recreational cannabis and more countries legalizing, this map shows that policy decisions are being made with enormous evidence gaps. The finding that most studies just measure cannabis use, not downstream health or socioeconomic outcomes, is a systemic weakness.
The numbers in context
447 studies included. 438 primary, 9 systematic reviews. 113 distinct outcomes. Over half with 3 or fewer studies. 5 of 7 systematic reviews rated minimal quality. Most research from US.
How the study worked
Evidence and gap map following Campbell Collaboration methodology. Searched 23 academic databases and 11 gray literature sources through August 2020. Dual screening and extraction with third-person deconfliction. Maryland Scientific Methods Scale for primary studies, AMSTAR 2 for reviews.
What this study cannot tell us
Maps evidence availability, not evidence quality or findings. Search through August 2020 may miss recent studies. English-language studies only. Evidence gaps identified do not necessarily indicate negative effects exist; they indicate effects are unstudied.
How to read the evidence
Rigorous evidence gap map using Campbell Collaboration methodology. Comprehensive search across 23 databases.
When this study was published
Published in 2023 searching through August 2020.
The bigger picture
This is the most comprehensive mapping of cannabis policy research ever conducted. Its finding that the evidence base is shallow on the outcomes that matter most (long-term health, safety, socioeconomic effects) should be a wake-up call for research funders and policy makers.
Questions still open
- Will research funding shift toward the understudied long-term outcomes?
- How should policy makers weigh evidence from areas with thin research bases?
Common questions
How much do we know about cannabis legalization effects?
What topics need more research?
Read the original research
Health, safety, and socioeconomic impacts of cannabis liberalization laws: An evidence and gap map.
Campbell systematic reviews, 19(4), e1362
Citation
Sevigny, Eric L; Greathouse, Jared; Medhin, Danye N. (2023). Health, safety, and socioeconomic impacts of cannabis liberalization laws: An evidence and gap map.. Campbell systematic reviews, 19(4), e1362. https://doi.org/10.1002/cl2.1362