MedWire News: Cannabis use is significantly more common among patients with bipolar disorder (BD) than those of similar age, gender, and ethnicity in the general population who do not have the mood condition, researchers report.
Arpana Agrawal (Washington University School of Medicine, Saint Louis, USA) and team also found that cannabis abuse/dependence is independently associated with an increased risk for BD-related disability, as well as suicide attempts and mixed episodes.
The findings come from a study of 471 BD patients and 1761 mentally healthy controls who were matched for age, gender, and ethnicity.
All of the participants completed questionnaires detailing their use of cannabis and were assessed for DSM-IV substance use disorders. Patients with BD were also interviewed about disease-related disability by clinicians.
The researchers found that BD patients were 6.8 times more likely to have a lifetime history of cannabis use than controls, at 71.3% versus 26.8%. This association remained significant after adjusting for other forms of substance use (alcohol, nicotine, cocaine, and other illicit drugs).
Of the BD patients, 40.0% of cannabis users reported using the drug 21 or more times in a single year. And rates of cannabis abuse/dependence were high, with 30% of BD patients (72% of those who had used the drug at least 21 times in a single year) meeting criteria for DSM-IV cannabis use disorders.
DSM-IV cannabis use disorder was associated with increased BD-related disability. Indeed, 63.7% of those with cannabis use disorders reported disability, compared with only 44.5% of those not meeting cannabis use disorder criteria.
After controlling for sociodemographic, substance use, and psychiatric covariates, BD patients with cannabis use disorders were still 1.8 times more likely to report disability due to BD than those without such a history.
BD patients with cannabis use disorders were also slightly more likely to have experienced mixed episodes and attempted suicide than those without cannabis use disorders, at 53.6% versus 43.2%, and 60.9% versus 50.8%, respectively.
Agrawal and colleagues comment in the journal Psychiatry Research: "There is ongoing debate on the efficacy of medication for BD in individuals afflicted with comorbid substance use disorders and on the modifying effects of antipsychotic medication on the endogenous cannabinoid system."
They conclude: "BD cases with comorbid cannabis use disorders are a vulnerable population and continued efforts to identify integrated treatments for dually diagnosed patients is vital."
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