Using cannabis as a teenager increases the likelihood of depression and suicidal behaviour, new research has confirmed.
Doctors analysed eleven previous studies, covering more than 23,000 young people.
They warned that cannabis has a “devastating impact”, and urged teens to avoid using the drug.
In the largest study to date, researchers from the University of Oxford and McGill University in Canada found that using cannabis before the age of 18 increased the chance of developing depression by 37 per cent.
Published by the American Medical Association, the study found that around 60,000 cases of depression in the UK could be attributed to cannabis use in teenage years.
Researchers said the findings highlighted an important public health problem.
The team emphasised that teenagers should stop using the drug, and said greater education is needed for parents who have a relaxed attitude to it.
Professor Andrea Cipriani, the study’s co-author, said: “The number of people who are exposed to cannabis, especially in this vulnerable age, is very high”.
He added: “Now we know that, especially for teenagers, there may be an effect which is biological, with some consequences which can be devastating”.
The Times editorial welcomed the findings, saying: “The new study creates the most robust link between youthful cannabis use and depression.”
The newspaper also encouraged parents to be better informed about the danger the drug poses for their children.
It concluded that “too little attention has been paid to the drug’s far wider psychological impact, which is anything but benign”.