Rates of substance use are higher in people with mental health problems compared to the general population and particularly in people with bipolar disorder, with cannabis the street drug most frequently used. Estimates suggest that up to 64% of this group have tried cannabis at least once in their lives, against about 30% of those without the disorder, despite only being about 2% of the overall population.
Specific reasons for the high levels of cannabis use in bipolar disorder are not yet fully understood. Retrospective studies (using case histories and qualitative interviews) suggest that individuals see cannabis as sometimes useful for managing symptoms of mania and depression. However, a number of large scale research studies have found that cannabis use is associated with significantly more manic and depressive episodes.