By Mark Cowen, Senior medwireNews Reporter - 12 April 2013
Compr Psychiatry 2013; Advance online publication
medwireNews: People with mental illnesses have a significantly higher prevalence of cannabis use and cannabis use disorders (CUDs) than mentally healthy individuals, researchers report.
"Extrapolating our results to the general population, we estimate that persons with a diagnosable primary mental illness constitute almost 75% of all cannabis users, with a particularly high prevalence of more frequent cannabis use and CUDs in this population," say Shaul Lev-Ran (Centre for Addiction and Mental Health, Toronto, Ontario, Canada) and team.
The prevalence of cannabis use and CUDs (cannabis abuse or dependence as defined by DSM-IV criteria) was particularly increased among patients with certain personality disorders (PDs) and bipolar I disorder.
The researchers studied data on 43,070 individuals, aged 18 years and older, who participated in the 2001-2002 National Epidemiologic Survey on Alcohol and Related Conditions.
Of the respondents, 12,659 had experienced mood, anxiety, personality, or substance abuse disorders (SUDs) in the previous 12 months.
The researchers found that the prevalence of weekly cannabis use, less than weekly cannabis use, and CUDs over the past 12 months among individuals with mental health disorders was 4.4%, 5.4% and 4.0%, respectively, compared with corresponding rates of 0.6%, 1.1% and 0.4% among those without mental illnesses.
Weekly cannabis use and CUD rates were highest among individuals with antisocial PD (13.4 and 12.0%, respectively), dependent PD (10.5 and 14.2%, respectively), histrionic PD (9.9 and 9.8%, respectively), and bipolar I disorder (9.6 and 9.4%, respectively).
Overall, 72.2% of all individuals who used cannabis and 81.8% of those with CUDs had a mental illness.
After accounting for sociodemographic variables, the team found that respondents with a mental illness were a significant 5.2 times more likely to have used cannabis in the past 12 months than those without a mental illness. This increased risk remained significant after further adjustment for any non-cannabis SUD, at an odds ratio of 2.5.
In addition, individuals with a mental illness were 8.0 times more likely to have CUDs than mentally healthy individuals, after adjustment for sociodemographic variables. And this increased risk also remained significant after further adjustment for non-cannabis SUDs, at an odds ratio of 3.2.
Lev-Ran et al conclude in Comprehensive Psychiatry: "Our findings emphasize the importance of proper screening for frequent cannabis use and CUDs particularly among individuals with mental illness, and focusing prevention and treatment efforts on the mentally ill."
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