The phrase “cannabis and mental health” conjures thoughts of anxiety, depression and schizophrenia. However, bipolar disorder is rarely considered from the perspective of the endocannabinoid system in mental health. Iranian researchers at Kerman University recently reviewed the beneficial and harmful aspects of endocannabinoids in this disease. First the bad news: There is an association between daily cannabis use and earlier onset of bipolar disorder (although interpreting cause-and-effect from these studies is rarely appropriate). And despite CBD’s potential anti-anxiety and anti-depressant effects, large doses of oral CBD has not prevented manic episodes in a few human trials. But there is good news too! Activating the CB2 receptor is promising on many levels. Bipolar disorder, like most neurological diseases, involves brain inflammation. The authors describe numerous molecular pathways through which CB2 attenuates inflammation and can protect neurons from harm. Moreover, we should note that psychiatric problems are often related to gut dysfunction, which cannabinoids can ameliorate. Green leafy vegetables, rich in β-caryophyllene, are one of the best dietary sources of chemicals that activate CB2. The Iranian scientists go on to describe how a breakdown product of endocannabinoids — called arachidonic acid — promotes abnormally high levels of inflammation in bipolar patients. The relationship between endocannabinoids and these inflammatory molecules is complex, but it provides a promising avenue for future research. There is reason to study compounds which differentially modulate cannabinoid receptors, blocking CB1 while activating CB2, in the treatment of bipolar disorder.