Smoking cannabis as a teenager could increase your risk of depression in adulthood by as much as 37%, new research suggests.
The researchers, from the University of Oxford and McGill University in Canada, analysed data from 11 studies involving more than 23,000 people – and described it as the largest meta-analysis to date in this field.
Up to 60,000 UK cases of adult depression could potentially be avoided if teenagers did not smoke cannabis, they said, warning parents not to be relaxed about the drug.
They also warned cannabis was a “significant public health risk” and called for officials to make tackling use of the drug a priority.
The study included teenagers who had used cannabis at least once before the age of 18 and did not distinguish between the frequency of use. It is thought that cannabis may alter the development of parts of adolescent brains.
The research found cannabis use before the age of 18 was linked to a 37% increased risk of a person developing depression before the age of 35.
“It’s a big public health and mental health problem, we think,” co-author Professor Andrea Cipriani, from the University of Oxford, said. “The number of people who are exposed to cannabis, especially in this vulnerable age, is very high and I think this should be a priority for public health and the mental health sector.”
In England, about 4% of teens aged 11 to 15 years old are estimated to have used cannabis within the last month.
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Animals studies have previously suggested a link between exposure to cannabinoids, the active component of cannabis, and the onset of depressive symptoms in adulthood.
However, the scientists said while they had found a link between cannabis and depression, the data can’t say for certain that cannabis causes depression.
“Although the size of 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 young generations makes it an important public health issue,” said Professor Cipriani.
“Regular use during adolescence is associated with lower achievement at school, addiction psychosis and neuropsychological decline, increased risk of motor vehicle crashes, as well as the respiratory problems that are associated with smoking.”
Research shows 10% of regular cannabis users become dependent on it, according to the NHS, and the risk of getting addicted is higher if you start using it in your teens or use it every day.
If you need help quitting cannabis, you can speak to your GP or call the Talk To Frank helpline on 0300 1236600. If you smoke cannabis with tobacco, the NHS’s advice on quitting smoking could also help.