The evidence on cannabis liberalization laws is unevenly distributed across policies and outcomes, and the research remains under-reviewed
An evidence and gap map (EGM) provides a systematic and visual representation of available research on a specific issue or topic. This EGM presents evidence on the effects of cannabis policies. The map reveals areas of both evidence concentration, which can aid systematic review and policy decisions, and evidence gaps, which can inform research and funding priorities.
Studies examining the effects of medical and recreational cannabis laws on cannabis use are relatively common. The evidence base for other laws and outcomes remains underdeveloped.
The interactive EGM is available here.
What is this EGM about?
The map provides descriptive and interactive displays of empirical evidence on the effects of cannabis liberalization laws. Specific interventions include laws that create or expand access to cannabis by removing criminal penalties, allowing medical use, or legalizing use for adults. Main outcomes include health, safety, and socioeconomic factors that are potentially linked to cannabis liberalization.
What is the aim of this evidence and gap map (EGM)?
The aim of this EGM is to present evidence on the effects of cannabis liberalization laws, including laws that create or expand access to cannabis by removing criminal penalties, allowing medical use, or legalizing use for adults.
What studies are included?
The EGM includes 447 studies, comprising 438 primary studies and nine systematic reviews. Eligible studies included works published in English since 1970 that employed quasi-experimental designs.
What are the main findings of this map?
Most cannabis liberalization research focuses on the effects of medical cannabis laws and recreational cannabis laws. These studies primarily investigate overall effects, but a sizable number also explore the specific effects of cannabis dispensaries.
Studies targeting other relevant laws—including medical cannabidiol laws, industrial hemp laws, and cultivation decriminalization laws—are relatively rare.
The map documented 113 distinct outcomes, with cannabis use outcomes investigated most frequently.
Although no geographic restrictions were applied, most of the evidence is from North America, predominantly the USA.
The systematic evidence base is relatively small, comprising just seven completed reviews on cannabis use, opioid-related harms, and alcohol-related outcomes. Five reviews were assessed as minimal quality and two as low quality.
How up-to-date is this EGM?
The literature search is current through 15 August 2020, with final study additions from other sources occurring on 12 November 2020.
Campbell is an international, voluntary, non-profit research network that publishes systematic reviews. We summarise and evaluate the quality of evidence about programmes in the social and behavioural sciences. Our aim is to help people make better choices and better policy decisions.