RESUMO
BACKGROUND: Research shows that the use of cannabis has a negative impact on the onset and outcome of schizophrenia, but little is known about possible effects on mood disorders. AIM: To study the influence of cannabis use on clinical and social treatment outcomes in patients with bipolar disorders who had been treated for a period of 12 months. METHOD: 3459 bipolar patients were enrolled in an observational study. The influence of cannabis on various clinical and social treatment outcomes was examined over a period of one year. In addition, tests were applied in order to find out whether third, mediating variables had effects on possible associations between cannabis use and treatment outcomes. RESULTS: During 12 months of treatment cannabis users showed less compliance and higher levels of illness severity, mania and psychosis than did non-users. In addition, cannabis users were less satisfied with their lives and had less chance of forming relationships than non-users. There was little evidence that associations between cannabis use and treatment outcomes were mediated by third variables. CONCLUSION: Cannabis use clearly had an independent impact on clinical treatment outcomes in patients with bipolar disorder, but the impact on social outcomes was only modest.