To explore whether cannabis has a potential role in actually causing bipolar disorder, a general population cohort study design is informative. Cahill et al. reviewed the interactions between chronic cannabis use and cognitive compromise in bipolar disorder. In trying to understand the interaction between the cannabis and bipolar disorder, attention has been given to the endocannabinoid system. Ashton et al. have detailed the mechanisms of the endocannabinoid system that have been implicated in brain reward pathways, pain, sleep, mood and anxiety. The authors have acknowledged the difficulties with studying the cannabinoids, including issues with doses, mode of administration and tolerance. There is no doubt a great deal of comorbidity between bipolar disorder and cannabis use. There is also a growing body of evidence regarding the deleterious effects of cannabis use in patients with bipolar disorder.