Teenagers who use cannabis have a higher risk of developing depression and suicidal thoughts as young adults and should be made aware of those risks by parents and doctors, scientists say.
About seven per cent of cases of adolescent depression could be averted if cannabis use was eliminated, according to an analysis of data on mental illness among young people in the United States, Britain and Canada.
"Although the size of the negative effects of cannabis can vary (and) it is not possible to predict the exact risk for each teenager, the widespread use of cannabis among the young generations makes it an important public health issue," Oxford University professor and study co-lead Andrea Cipriani said.
In Canada, more than 20 per cent of teens aged 15 to 19 say they have used cannabis in the past year. In England, for those aged 11 to 15, about four per cent say they used cannabis in the last month.
The researchers said the results suggested that, if cannabis use were eliminated, there would be an estimated 400,000 fewer cases of depression in 18 to 34 year olds in the United States, 25,000 fewer in Canada and about 60,000 fewer in the Britain.
The study, published in the journal JAMA Psychiatry, included 23,317 people from 11 international studies and looked at depression, anxiety and having suicidal thoughts in young adults.
Australian Associated Press