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Are Smoking Pot and Psychosis Linked?

Marijuana Boosts Later Psychotic Illness Risk by 40%, Study Shows

Lancet Editors Change Tune

In an accompanying comment, two scientists from Copenhagen University Hospital echo Zammit's belief that "there is a need to warn the public of these dangers, as well as to establish treatment to help young, frequent cannabis users."

In an editorial in the same issue, Lancet editors note that the publication ran an oft-quoted editorial in a 1995 issue stating that "the smoking of cannabis, even long term, is not harmful to health." Now, the editors note, research published in the interim, including the meta-analysis, has triggered a change in their thinking, with them now stating that cannabis use "could increase the risk of psychotic illness" and that more research is needed on any link with depression and anxiety.

NORML Begs to Differ

If the association exists between marijuana use and psychotic illness, "we would have seen the negative effects they were warning about if they were significant," says Paul Armentano, a senior policy analyst for the National Organization for the Reform of Marijuana Laws (NORML), based in Washington.

Most Western cultures, he tells WebMD, have witnessed "an explosion among marijuana use among adults and young people.

"Where is the explosion in cannabis-related mental illness?" he asks. "The paper says, 'You are right, we haven't seen it. Maybe it is a delayed reaction.'"

Armentano argues the rise in mental illness would have already occurred if the link exists.

Armentano also wonders if the psychosis may have come first, before the marijuana use, for some people. In the paper, the authors note that such reverse causation is not likely for psychosis but that the studies of marijuana and depression did not adequately address the possibility of reverse causation.

Politics in the U.K. may be driving the effort to analyze an association between marijuana and mental illness, Armentano tells WebMD. Prime Minister Gordon Brown has been quoted in the British press as saying he has never used cannabis, even as cabinet ministers tell about their cannabis-filled younger days. In 2004, the U.K. downgraded cannabis to a class C drug, reducing penalties for possession, production, and supply.

Now, the Advisory Council on the Misuse of Drugs in the U.K. will look at evidence for harms caused by cannabis and discuss whether the drug should be relabeled, perhaps as a class B drug of misuse, with stiffer penalties for possession.

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