Should Burden of Disease Estimates Include Cannabis Use as a Risk Factor for Psychosis?

Comparative risk assessments estimate the proportion of a disease that can be attributed to a particular risk exposure and are important guides for health planning. In observational studies, there has been consistent evidence that cannabis use is associated with an increased risk of schizophrenia and more generally, psychosis. There is debate about whether such observational evidence is sufficient to infer that cannabis use is a contributory cause of psychosis. Given the controversy, should the comparative risk assessment in the current revision of the Global Burden of Disease (GBD) include an attribution of psychosis to cannabis use? We argue that the risk assessment should be included because the evidence is as good as that for many other risk factors included in the GBD, psychotic disorders are associated with substantial unavertable disability, and cannabis use is a potentially preventable exposure.