LONDON – Using marijuana seems to increase the chance of becoming psychotic, researchers report in an analysis of past research that re-ignites the issue of whether pot is dangerous.
The new review suggests that even infrequent use could raise the small but real risk of this serious mental illness by 40 percent.
Doctors have long suspected a connection and say the latest findings underline the need to highlight marijuana’s long-term risks. The research, paid for by the British Health Department, is being published today in medical journal The Lancet.
“The available evidence now suggests that cannabis is not as harmless as many people think,” said Dr. Stanley Zammit, one of the study’s authors and a lecturer in the department of psychological medicine at Cardiff University.
The researchers said they couldn’t prove that marijuana use itself increases the risk of psychosis, a category of several disorders with schizophrenia being the most commonly known.
There could be something else about marijuana users, “like their tendency to use other drugs or certain personality traits, that could be causing the psychoses,” Zammit said.
Zammit said the risk of developing schizophrenia for most people is less than 1 percent. The prevalence of schizophrenia is believed to be about five in 1,000 people. But because of the drug’s wide popularity, the researchers estimate that about 800 new cases of psychosis could be prevented by reducing marijuana use.
The scientists found a more disturbing outlook for “heavy users” of pot, those who used it daily or weekly: Their risk for psychosis jumped by a range of 50 percent to 200 percent.
One doctor noted that people with a history of mental illness in their families could be at higher risk. For them, marijuana use “could unmask the underlying schizophrenia,” said Dr. Deepak D’Souza, an associate professor of psychiatry at Yale University.
Some experts say governments should now work to dispel the misconception that marijuana is a benign drug.
“We’ve reached the end of the road with these kinds of studies,” said Dr. Robin Murray of King’s College, who had no role in the Lancet study. “Experts are now agreed on the connection between cannabis and psychoses. What we need now is for 14-year-olds to know it.”
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