We’re seeing a frightening upswing in depression among teenagers.
There are several factors behind it, including social media use and post-traumatic stress disorder.
But could cannabis use be part of the picture too?
It seems so, according to the first study of its kind.
Teenagers who use cannabis are a third more likely to suffer depression and three times as likely to attempt suicide.
Tens of thousands of cases of depression are likely to be the result of cannabis use among the under-18s.
About one in 13 children aged 11 to 15 uses cannabis, rising to one in six aged 16 to 24.
We’ve long been concerned that its active ingredient, THC, harms the brain at a crucial stage of development.
The drug has been linked to a fivefold increase in the risk of psychosis but a connection with depression hadn’t been previously established.
Researchers have now analysed 11 studies that looked at data on 23,000 people.
Those who used cannabis before the age of 18 were 37% more likely to develop depression by the age of 32 than those who did not. They were also more than three times as likely to attempt suicide.
“Especially for teenagers, there may be an effect which is biological, with some consequences which can be devastating,” said Andrea Cipriani, one of the authors based at Oxford University.
“Young people should be aware of the risk.”
Dr Cipriani explained he had included only the most rigorous studies, which showed the cannabis use came before the depression, and took account of the other mental health risks. The results are robust.
He estimates that of one in 14 of depression cases in young adults, about 60,000 cases, could be attributable to cannabis use as teenagers.
“We know that use of cannabis is very common so the impact is not negligible,” he said.
“The message is that there may be a risk of developing depression among teenagers who use cannabis.”
Cannabis is getting stronger and in Britain high-potency skunk is the most widely used, but its long-term effects are unknown.
Dr Cipriani said: “I think we need to stress the importance of education and prevention programmes.”
Damage can be permanent. The correlation between cannabis use and poor mental health is undisputed. But new research reveals teenagers and young adults who smoke cannabis are more likely to become anxious and depressed, even considering suicide more than non-users.
Cannabis supporters argue that it’s those youngsters already prone to depression who are most likely to try cannabis. Even so, they should be aware of its dangers.