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Tijdschrift voor Psychiatrie 52 (2010) 5, 287 - 298

New research

The influence of cannabis on the course of bipolar disorder: a longitudinal analysis

I. Winter-van Rossum, M.M. Boomsma, D.E. Tenback, C. Reed, J. van Os

summary
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.

keywords bipolar disorder, cannabis use, treatment outcome