The impact of legal cannabis availability on cannabis use and health outcomes: A systematic review (2023)

Background: For alcohol, regulating availability is an effective way to reduce consumption and harm. Similarly, the higher availability of medical cannabis dispensaries has been linked to increased cannabis consumption and harm. For recreational cannabis markets, such a link is suspected but still poorly understood.
Methods: A systematic literature review (PROSPERO registration number 342357) was conducted on 1 July 2022 in common libraries (Medline, Web of Science, PsycInfo, Psyndex, CINAHL, Embase, SCOPUS, Cochrane) for publications since 2012. Studies linking variations in the availability of legal cannabis products to behavioral outcomes (cannabis use or related health indicators) were included, while studies focusing solely on the legalization of medical cannabis were excluded. The risk of bias was assessed using an adapted version of the Newcastle-Ottawa-Scale.
Results: After screening n = 6,253 studies, n = 136 were selected for full-text review, out of which n = 13 met the inclusion criteria, reporting on n = 333,550 study participants and n = 855,630 presentations to emergency departments. All studies were conducted in North America, with the majority from Western US states. Using longitudinal (n = 1), cross-sectional (n = 4), or repeated cross-sectional (n = 8) study designs, an increased availability of legal cannabis was linked to increased current cannabis use and health-related outcomes (vomiting, psychosis, or cannabis-involved pregnancies), regardless of the indicator employed to measure availability (proximity or density) among both adults and adolescents. The positive correlation between cannabis availability and consumption is most pronounced among those groups who have been less exposed to cannabis before legalization. The association between the availability of legal cannabis and risky use indicators was less consistent.
Conclusions: Groups who have been least exposed to cannabis before legalization may be most susceptible to increased availability. In jurisdictions with legal cannabis markets, restrictions on the number of legal cannabis retailers, especially in densely populated areas, appear warranted.