British teenage cannabis smokers risk depression

About 60,000 British teenagers who took cannabis are at increased risk of depression and suicide, a major study revealed Wednesday.

Researchers at Oxford University and McGill University in Montreal, Canada, found a seven percent increased risk of depression and suicidal behaviour in people who took cannabis as adolescents.

The class B drug is already known to cause psychosis, but the research is one of the first to examine links with more common mental disorders such as depression and anxiety.

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.

The study said that more than 400,000 adolescent cases of depression in the U.S., 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, according to the study. Nor was the type or quantity of cannabis examined in terms of how much was needed to cause a negative impact.