The role played by evidence on the effects of cannabis use in cannabis policy 1992-2022

Before 2000 associations between cannabis use and adverse health outcomes were used by US government to support prohibition. Since 2000, advocates of cannabis legalisation and lobbyists for a legal cannabis industry have provided increasingly positive assessments of the safety and effectiveness of medical uses of cannabis. Associations between cannabis use and improved health outcomes have been interpreted causally while observational evidence of harm dismissed as 'correlational'. The onus of proof is increasingly falling on public health advocates of more restrictive cannabis regulation to prove it is necessary rather than on the cannabis industry to justify its absence, as for example the regulation of cannabis potency.

There has been a major change in the way that observational evidence on the risks and benefits of cannabis use has been interpreted as cannabis policy has been liberalised. Evidence of the putative medical benefits of cannabis is increasingly uncritically while evidence of harm is increasingly discounted. Effective regulation of a legal market requires more even-handed assessments of both the risks and the benefits of cannabis use.