Smoking marijuana (also called cannabis) is unlikely to increase a person's risk of killing themselves later on, an analysis of more than three decades worth of death records on more than 50,000 Swedish military recruits suggests.
"I don't think this can be interpreted as saying, 'Well, there are no risks of using cannabis,'" Dr. Stanley Zammit of the department of psychological medicine at Cardiff University School of Medicine in the UK told Reuters Health.
Nevertheless, "we can pretty much rule out a strong effect of cannabis on long-term risk of suicide whether it's through depression or whatever," he added.
Zammit and his colleagues had previously found a link between cannabis use and schizophrenia while looking at the same group of 50,087 men drafted into the Swedish military in 1969-1970. Nearly all were 18 to 20 years old at the time. In that first analysis, the researchers had also found a "much less consistent and overall weaker" relationship between cannabis use and depression, anxiety, suicidal thoughts, and suicide.
To investigate further, Zammit and his team identified suicides among the recruits over the next 33 years in Sweden's National Cause of Death Registry. During that time, there were 600 suicides or deaths from unknown causes.
At the time they were drafted, about one in ten of the men admitted to ever using cannabis. These men were 62 percent more likely to have killed themselves during the follow-up period than men who had never used marijuana.
But once the researchers adjusted for factors that could influence both pot use and suicide risk, such as behavior problems in childhood, psychological adjustment, psychiatric diagnoses, drinking, smoking, and parental drug use, the increased risk of suicide associated with marijuana disappeared.
While the findings suggest that marijuana use is not a strong risk factor for suicide, Zammit said, they do support the possibility that cannabis use may have a causal relationship with psychosis. He and his colleagues are investigating the schizophrenia-cannabis link further, for example determining whether the potency of cannabis plays a role in psychosis risk.
SOURCE: The British Journal of Psychiatry, December 2009.
January 15, 2010