Cannabis use and expression of mania in the general population.
BACKGROUND
Cannabis use is common in patients with bipolar disorder, however little is known about cannabis as a risk factor for mania. In order to investigate the association between exposure to cannabis and subsequent development of manic symptoms whilst controlling for psychotic symptoms, a longitudinal population-based study was carried out.


METHODS
4815 individuals aged 18 to 64 years were interviewed using the Composite International Diagnostic Interview at baseline, 1 year follow up and 3 year follow up, including assessment of substance use, manic symptoms and psychotic symptoms.


RESULTS
Use of cannabis at baseline increased the risk for manic symptoms during follow-up (adjusted OR 2.70, 95% CI: 1.54, 4.75), adjusted for age, sex, educational level, ethnicity, single marital status, neuroticism, use of other drugs, use of alcohol, depressive symptoms and manic symptoms at baseline. The association between cannabis use and mania was independent of the prevalence and the incidence of psychotic symptoms. There was no evidence for reverse causality, as manic symptoms at baseline did not predict the onset of cannabis use during follow-up (OR = 0.35, 95% CI: 0.03, 3.49).


CONCLUSIONS
As 3 years is a relative short period of follow-up, long-term effects of cannabis use on mania outcomes could not be detected.


CONCLUSIONS
The results suggest that cannabis use may affect population expression of manic symptoms (and subsequent risk to develop bipolar disorder [Regeer, E.J., Krabbendam, L., R, DE Graaf, Ten Have, M., Nolen, W.A., Van Os, J., 2006. A prospective study of the transition rates of subthreshold (hypo)mania and depression in the general population. Psychol Med, 1-9.]). These findings may not be due to the emergence of psychotic symptoms or the effects of self-medication.
Henquet
Cécile
C
Department of Psychiatry and Neuropsychology, South Limburg Mental Health Research and Teaching Network, EURON, Maastricht University, Maastricht, The Netherlands.
Krabbendam
Lydia
L
de Graaf
Ron
R
ten Have
Margreet
M
van Os
Jim
J
D000293:Adolescent; D000328:Adult; D001714:Bipolar Disorder / Q000139:chemically induced* / Q000453:epidemiology; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D008297:Male; D008385:Marijuana Smoking / Q000009:adverse effects*; D008875:Middle Aged; D009426:Netherlands / Q000453:epidemiology; D011618:Psychotic Disorders / Q000453:epidemiology*; D012306:Risk