Smoking cannabis just five times as a teenager raises the risk of psychosis, new research suggests.
Scientists have today uncovered further evidence the drug, commonly smoked by youngsters, leads to poor mental health.
The findings, led by Finnish researchers, back-up an array of evidence that shows cannabis can drive some to the point of suicide.
University of Oulo scientists revealed the earlier someone begins smoking the drug, the more likely they are to develop psychosis.
It comes amid prominent warnings by campaigners that super-strength skunk has flooded Britain’s illegal market at a worrying rate.
Scientists have today uncovered further evidence cannabis, commonly smoked by youngsters, leads to poor mental health
Skunk, the potent form of the drug, is responsible for a quarter of new cases of psychotic mental illness, a landmark study two years ago declared.
And the new research, published in The British Journal of Psychiatry, provides a further link between cannabis and psychosis.
How was the study carried out?
More than 6,000 volunteers were tracked from their 15th birthday until they turned 30 to assess their risk of the condition.
Figures estimate that around one per cent of the population suffer from psychosis, which can cause delusions, such as hearing voices, and lead to severe distress.
An analysis, which involved PhD student Antti Mustonen, showed a link between smoking cannabis and going on to develop psychosis.
What did the researchers say?
He said: ‘We found that young people who had used cannabis at least five times had a heightened risk of psychoses during the follow-up.
‘Our findings are in line with current views of heavy cannabis use, particularly when begun at an early age, being linked to an increased risk of psychosis.
‘Based on our results, it’s very important that we take notice of cannabis-using young people who report symptoms of psychosis.’
Mr Mustonen, who worked alongside Cambridge and Queensland experts, added: ‘If possible, we should strive to prevent early-stage cannabis use.’
Cigarettes linked to psychosis
A separate study, published in Acta Psychiatrica Scandinavica, delved into the link between smoking cigarettes and psychosis.
An analysis of the same participants revealed teenagers who smoke 10 cigarettes face a higher risk of suffering from psychosis.
The risk is also raised if the smoking starts before the age of 13, according to the research, led by Professor Jouko Miettunen.
He explained the findings were true even when accounting for other factors that raise the risk, including a family history of psychosis.
‘Based on the results, prevention of adolescent smoking is likely to have positive effects on the mental health of the population in later life,’ he said.
Ian Hamilton, a lecturer in mental health at York University, told MailOnline that it was ‘worrying’. He added: ‘People with mental health problems are more likely to smoke.
‘This study suggests this is no accident as smoking appears to increase the risk of developing serious mental health problems such as psychosis.
‘We need to do much more to encourage people with mental health problems to think about quitting and provide them with the help to do this.
‘Smoking is one of the main reasons that people with severe mental health problems die decades before those who don’t, something that we can potentially improve.’