Up to 60,000 UK cases of adult depression could potentially be avoided if teenagers did not smoke cannabis, new research suggests.
Smoking the drug before the age of 18 is linked with an increased risk of depression and suicide in adulthood, according to a study published in journal JAMA Psychiatry.
The researchers warned cannabis was a significant public health risk, as they called for officials to make tackling use of the drug a priority.
‘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.’
The researchers analysed data from 11 studies involving more than 23,000 individuals and described it as the largest meta-analysis to date in this field.
About 7% of cases of adult depression may possibly not occur if teenagers stopped smoking cannabis, they found.
This means at any one time up to 60,000 cases among 18 to 34-year-olds in the UK and 400,000 in the US could be attributable to use of the drug during adolescence, they suggest.
However, a link was not found between cannabis exposure and anxiety in adulthood.
While the risk of depression is modest, the researchers said the common use of cannabis among teenagers makes it a concern.
In England, about 4% of adolescents aged 11 to 15 years old in England are estimated to have used the drug within the last month.
Animals studies have suggested a link between exposure to cannabinoids, the active component of cannabis, and the onset of depressive symptoms in adulthood.
It is thought that cannabis may alter the development of parts of adolescent brains.
Professor Cipriani said: ‘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.
‘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.’
The study, by researchers at McGill University and the University of Oxford, included teenagers who had used cannabis at least once before the age of 18 and did not distinguish between the frequency of use.