Cannabis Risks and Benefits: An Umbrella Review
An August 2023 umbrella review in BMJ synthesized 101 meta-analyses of cannabis-related research — making it one of the largest evidence syntheses available. The conclusion was asymmetric: harms are well-supported by high-quality evidence, while many of the claimed benefits (especially recreational and medicinal claims that don't relate to specific cannabinoid-derived drugs) rest on weak or low-quality evidence.
Harms with the strongest evidence include psychosis risk, cognitive impairment, cannabis use disorder, motor-vehicle crashes, respiratory issues from smoking, and adverse outcomes in pregnancy. Many claimed benefits — improved sleep, anxiety relief, broad pain management — show much weaker evidence than the popular narrative suggests.
This page is a draft. The full writeup will summarize the evidence-strength rankings across each outcome category.