background Research suggests that cannabis use impacts negatively on onset and outcome of schizophrenia, but less is known about possible effects in mood disorders.

aim The first study analysing the influence of cannabis exposure on both clinical and social treatment outcomes within a bipolar (bp) population over the course of 1 year is presented.

method 3459 bipolar patients were enrolled in the emblem study, a large European observational study. The influence of cannabis exposure on clinical and social treatment outcome measures was examined over the course of 1 year, as well as the effects on these associations of third, mediating, variables.

results Over 12 months of treatment, cannabis users exhibited less compliance and higher levels of overall illness severity, mania and psychosis compared to non-users. In terms of social outcome, it was observed that cannabis users engaged more frequently in social activities whilst having a lower probability of having a relationship. Users also experienced less satisfaction with life compared to non-users. Third variables, in particular abuse of alcohol and other substances, (partly) reduced various associations.

conclusion An impact of cannabis use on psychopathological outcomes in patients with bp was apparent, whereas the impact on social outcomes was modest. Much of the impact of cannabis use on outcome, including psychosis, may also be associated with the use of alcohol and other drugs. Understanding the direct and, in particular, the indirect pathways from cannabis use to outcome may offer valuable insights into treatment strategies in bipolar illness.