Site Presented By
Sunday, Nov 8, 2009
According to Murray, the latest available data shows that the consumption of cannabis is a key risk factor for the development of serious mental illness. With regard to schizophrenia, the campaign cites one study of nearly 50,000 Swedish soldiers between the ages of 18 and 20, published in the British Medical Journal in 2002, which found that those who had smoked pot more than 50 times had a rate of schizophrenia nearly seven times as high as those who did not use marijuana at all.
The American Psychiatric Association is one of the major groups backing the campaign; a spokesperson referred to part of the group's policy statement as the reason for its endorsement: "The American Psychiatric Association is concerned and opposed to the use of drugs and alcohol in children."
Yet leading experts in psychiatric epidemiology (whom the APA recommended contacting, but who do not officially speak for the organization) are far from convinced about causal connections between marijuana and serious mental illness. One key problem, they say, is that it's very difficult to determine whether pot smoking predisposes people to schizophrenia or whether early symptoms of schizophrenia predispose people to smoking pot -- or whether some third factor causes some people to be more vulnerable to both.
In the Swedish study, for example, when factors already known to increase risk for schizophrenia were removed, such as a childhood history of disturbed behavior, the connection between marijuana use and risk for the disease was substantially reduced. Just one or two additional unknown influences could potentially wipe out the apparent marijuana-schizophrenia link, according to Dr. William Carpenter, a professor of psychiatry and pharmacology at the University of Maryland. Carpenter noted in a letter published in the British Journal of Psychiatry in October 2004 that the same genes that predispose someone to schizophrenia might also predispose them to substance abuse, but that drug use might start earlier simply because many people start using drugs in their teen years, while schizophrenia most commonly begins in the early 20s.
Perhaps the strongest piece of evidence to cast doubt on a causal connection between marijuana and schizophrenia is a long flat-line trend in the disease. While marijuana use rose from virtually nil in the 1940s and '50s to a peak period of use in 1979 -- when some 60 percent of high school seniors had tried it -- schizophrenia rates remained virtually constant over those decades. The same remains true today: One percent or fewer people have schizophrenia, a rate consistent among populations around the world. This is in stark contrast to studies linking tobacco smoking with lung cancer, where rises in tobacco use were accompanied by rising rates of lung cancer.
"If anything, the studies seem to show a possible decline in schizophrenia from the '40s and the '50s," says Dr. Alan Brown, a professor of psychiatry and epidemiology at Columbia University. "If marijuana does have a causal role in schizophrenia, and that's still questionable, it may only play a role in a small percent of cases."
For the tiny proportion of people who are at high risk for schizophrenia (those with a family history of the illness, for example), experts are united in thinking that marijuana could pose serious danger. For those susceptible, smoking marijuana could determine when their first psychotic episode occurs, and how bad it gets. A study published in 2004 in the American Journal of Psychiatry of 122 patients admitted to a Dutch hospital for schizophrenia for the first time found that, at least in men, marijuana users had their first psychotic episode nearly seven years earlier than those who did not use the drug. Because the neurotransmitters affected by marijuana are in brain regions known to be important to schizophrenia, there is a plausible biological mechanism by which marijuana could harm people prone to the disorder. Both Brown and Carpenter say that people with schizophrenia who smoke pot tend to have longer and more frequent psychotic episodes, and find it very difficult to quit using the drug.
Of course, the U.S. government's current ad campaign targets a much broader population than those highly vulnerable to schizophrenia, fanning fears based on a statistically rare scenario.
The campaign also declares that today's pot is more potent than the pot smoked by previous generations, implying heightened risk. Fine sinsemilla may seem more prevalent than ditchweed nowadays, but there is debate over whether today's average smoker is puffing on stronger stuff than the average stoner of the 1970s, as Daniel Forbes detailed in Slate. And, as Forbes showed, the drug czar's office has grossly exaggerated the numbers on this issue in the past.
Meanwhile, UCLA public policy expert Mark Kleiman has pointed out that federally funded research by the University of Michigan shows that since the 1970s the level of high reported by high school seniors who smoked marijuana has remained "flat as a pancake." In other words, even if today's kids are smoking more potent stuff, they don't get higher than their folks did -- like drinking a few whiskey shots rather than multiple mugs of beer, they use less of the good stuff to achieve the same effect.
