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A march in Brasilia calling for the legalisation of cannabisReuters

Teenagers who smoke a lot of marijuana could be prone to dying younger, according to the results of a new study. The results are from a study in Sweden of men who smoked the drug in the 1960s.

Swedish scientists followed the lives of around 50,000 men who took part in compulsory military service in the country between 1969 and 1970. They then monitored them on the country's national cause of death register for 42 years until 2011. Of the 50,000, 4,000 died, and research showed that those men who had smoked a lot of cannabis when they were 18 and 19 were 40% more likely to die by the age of 60 than those who had never tried it.

Stoners have short lives

The study, which was conducted by researchers at the Karolinska Institutet in Stockholm and published in the American Journal of Psychiatry, defined "heavy use" as smoking the drug 50 times or more. Amongst other findings, figures suggest that the risk of death from suicide or an accident was proportional to how much cannabis the men had consumed as teens.

Addiction expert Scott Krakower told CBS News in the US that "cannabis users have poorer health in general", and that "you'd expect there to be increased mortality risk".

"Marijuana users generally may have poorer diets and they might be tobacco smokers. There's an increased linkage between weed and tobacco," he said.

No risk of madness

The Swedish researchers focused on whether the men developed psychoses. It found that heavy cannabis use did not seem to increase the men's chances of developing that kind of psychological disorder.

"For the men who had suffered psychosis, the mortality rate was roughly four times higher, but this was independent of earlier cannabis use," said study leader Peter Allebeck. "Our conclusion is that early cannabis use can contribute to premature death, particularly through injuries and suicide, and that this is unrelated to the increased risk of psychosis."

However, in the study's conclusion the scientists warned these results contradicted earlier results of the study. And they admitted the results "should be interpreted with caution because of a lack of information" on the subjects after they left military service.