About 60,000 young Britons are at increased risk of depression and suicide because they used cannabis as teenagers, a major study revealed today.
The class B drug is already known to cause psychosis but today’s research is one of the first to examine links with more common mental disorders such as depression and anxiety.
Researchers at Oxford University and McGill University in Montreal found a seven per cent increased risk of depression and suicidal behaviour in people who took cannabis as adolescents.
Though the risk was described as “modest” on an individual level, it has raised “much more serious” concerns about the wider population impact because cannabis use is so prevalent.
It said that more than 400,000 adolescent cases of depression in the US, 60,000 in the UK and 25,000 in Canada were potentially attributable to cannabis exposure.
The findings were based on a “meta analysis” of 11 international studies conducted over 15 years and involving 23,317 people.
No direct “causative link” was found between cannabis use and depression or suicide. Nor was the type or quantity of cannabis examined in terms of how much was needed to cause a negative impact.
Professor Andrea Cipriani, of Oxford University, said: “We looked at the effects of cannabis because its use among young people is so common, but the long-term effects are still poorly understood.
“Although the negative effects of cannabis can vary between individual adolescents 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.
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“Regular use during adolescence is associated with lower achievement at school, addiction, psychosis and neuropsychological decline, and increased risk of motor vehicle crashes.”
Professor Sir Robin Murray, of King’s College London, said: “The finding that cannabis use is associated with a modest increase in risk of depression and suicide is probably correct.”
Dr Lindsey Hines, of the University of Bristol, said: “This research suggests that teenage cannabis use is still related to mental health in later years.”
