A new study suggests people with mental illness are more than seven times as likely to use marijuana weekly than people without a mental illness.

Although some research has found links between cannabis use and mental illness, until now, the exact numbers and prevalence of cannabis use had not been investigated. Cannabis is the most widely used illicit substance globally, with an estimated 203 million people reporting use.

“We know that people with mental illness consume more cannabis, perhaps partially as a way to self- medicate psychiatric symptoms, but this data showed us the degree of the correlation between cannabis use, misuse, and mental illness,” said lead research Shaul Lev-ran, M.D. “Based on the number individuals reporting weekly use, we see that people with mental illness use cannabis at high rates. This can be of concern because it could worsen the symptoms of their mental illness,” said Lev-ran.

Researchers also found that individuals with mental illness were 10 times more likely to have a cannabis use disorder. In this new study, published in the journal Comprehensive Psychiatry, researchers at Toronto’s Centre for Addiction and Mental Health (CAMH) analyzed U.S. data from face-to-face interviews with over 43,000 respondents over the age of 18 from the National Epidemiologic Survey on Alcohol and Related Conditions.

Using structured questionnaires, the researchers assessed cannabis use as well as various mental illnesses including depression, anxiety, drug and alcohol use disorders and personality disorders, based on criteria from the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV). Among those will mental illness reporting at least weekly cannabis use, rates of use were particularly elevated for those with bipolar disorder, personality disorders and other substance use disorders.

In total, 4.4 percent of individuals with a mental illness in the past 12 months reported using cannabis weekly, compared to 0.6 percent among individuals without any mental illness. Cannabis use disorders occurred among 4 percent of those with mental illness versus 0.4 per cent among those without.

Researchers also noted that, although cannabis use is generally higher among younger people, the association between mental illness and cannabis use was pervasive across most age groups. Experts believe the findings suggest those with mental illness may benefit from screening for frequent and problem cannabis use, so that targeted prevention and intervention may be employed as necessary.

Source: Centre for Addiction and Mental Health April 2013