Teenagers with bipolar disorder or depression who smoke cannabis are at increased risk of death and self-harm, a shock new study has found. .

Researchers from Ohio State University found teens with a mood disorder and a cannabis habit are 3.28 times more likely to self-harm and 59 per cent more at risk of dying from all causes.

Researchers from Ohio State University in the US found teens with a mood disorder and a cannabis habit are 3.28 times more likely to self-harm and 59 per cent more at risk of dying from all causes (stock) .

The risk of death from an unintended overdose is 2.4 higher than in people who avoid the drug, and the likelihood of being a victim of murder is 3.24 times higher, the study finds. 

The researchers say that not only are youths with mood disorders more likely to use cannabis, but the drug can also worsen symptoms and interfere with treatments. 

Amphetamine is the most under-reported drug, with the new study finding almost one in three (32.9 per cent) of 24-year-olds have taken the illegal drug

Cannabis has been taken by 60.5 per cent of people, up significantly from the lower estimate of 37.3 per cent, the study finds. 

Opioid use was statistically higher and has been taken by one in 20 people whereas sedatives or tranquilisers have been used by 11.6 per cent of young adults, up 8.1 per cent.