Cancer risk and legalisation of access to cannabis in the USA: overview of the evidence

Cannabis in the USA is transitioning from a nationwide illegal status to liberalisation for medicinal or recreational use across different jurisdictions. As the acceptability and accessibility of cannabis continue to grow, updated knowledge on the cancer risk from recreational cannabis use is necessary to inform recommendations by public health organisations, policy makers, and clinical practitioners. We reviewed the evidence to date. Our umbrella review of current global epidemiological evidence reveals that links between cannabis exposure and cancer risk are more suggestive than conclusive. The cancer type most closely linked to cannabis use is non-seminoma testicular cancer. However, evidence is emerging of an increased risk of other types of cancer (eg, lung squamous cell carcinoma, head and neck squamous cell carcinoma, and oral, breast, liver, cervical, laryngeal, pancreatic, thyroid, and childhood cancer), underscoring the potential importance of incorporating prevention and cessation of cannabis use in cancer prevention efforts. Our review also identified the need for replication of previous studies for additional epidemiological investigations that use rigorous study designs, and data collection protocols free from the biases of major confounders, misclassification, and measurement error in assessing cannabis exposure. Research on the long-term health and economic consequences of all cannabis products (both medical and recreational) are also needed. Currently, the insufficient evidence on the health risks of cannabis use reduces the ability of policy makers, health-care professionals, and individuals to make informed decisions about cannabis use and could expose the public to a potentially serious health risk.