SMOKING cannabis as a teenager could increase the risk of depression in adulthood by 37 per cent, a study led by an Oxford professor has revealed.

Senior clinical researcher at Oxford University Andrea Cipriani showed the developing brain in 11 to15-year-olds is at significant risk to the effect of the drug.

Prof Cipriani, who is also associate director in research and development at Oxford Health NHS Foundation Trust, said the size of the negative effects of cannabis can vary between individual adolescents and that widespread use of cannabis among the young generations makes it an important public health issue.

He added: “My bottom line message is that adolescents should avoid using cannabis. I think we should stress the importance of education and prevention programmes."

The landmark study analysed more than 23,000 people.