People with mental illnesses are more than seven times likely to use cannabis weekly, scientists claim.
Researchers from the Centre for Addiction and Mental Health (CAMH) in Canada also found that individuals with mental illness were 10 times more likely to have a cannabis use disorder.
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 Dr Shaul Lev-ran, Adjunct Scientist at CAMH and Head of Addiction Medicine at the Sheba Medical Center, Israel.
"Based on the number of 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.
In this new study, published in the journal Comprehensive Psychiatry, CAMH researchers analysed 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 per cent of individuals with a mental illness in the past 12 months reported using cannabis weekly, compared to 0.6 per cent among individuals without any mental illness.
Cannabis use disorders occurred among 4 per cent 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.
