A Systematic Mapping of 447 Studies on Cannabis Legalization Found Major Evidence Gaps on Long-Term Health and Socioeconomic Outcomes

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.

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.

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.

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.

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.