“The new review suggests that even infrequent use could raise the small but real risk of this serious mental illness by 40 per cent.… The research, paid for by the British Health Department, is being published Friday in medical journal The Lancet.”

“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."

"Dr Iddon, the chairman of the all-party parliamentary group on drugs misuse, said the study did not convince him it was time to return cannabis to class B. "I don't think the causal link has been proved. I think cannabis might - possibly for genetic reasons - trigger psychosis at an earlier age." The MP, who is also a member of the science and technology select committee, said there was a danger of criminalising "hundreds of thousands of young people" if the status of the drug was changed. "If Gordon Brown changes the class of the drug, it won't be evidence-based but for political reasons," he said.

It should also be pointed out that rates of alcoholism and drug abuse of all kinds are much higher in the schizophrenic population than in the general population and no one is claiming, for example, that alcohol abuse leads schizophrenia, indeed quite the opposite. The following explains the magnitude of the association.

“The Epidemiologic Catchment Area (ECA) study2 (2 The ECA study was a nationwide survey that used DSM–IV criteria to determine the prevalence of psychiatric disorders in the general population and among people in treatment.) found that 33.7 percent of people with a diagnosis of schizophrenia or schizophreniform disorder (a related disorder marked by the same symptoms as schizophrenia but lasting less than 6 months) also met the criteria for an AUD diagnosis at some time during their lives and that 47 percent met the criteria for any substance use disorder (excluding nicotine dependence) (Regier et al. 1990). Rates of substance use disorder tend to be higher among males and among people of both genders and all ages in institutional settings, such as hospitals, emergency rooms, jails, and homeless shelters. This holds true for people with and without schizophrenia (Regier et al. 1990).”

Update: CBC's the National

Mitch Earleywine a professor of psychology at the University of Southern California leveled an important methodological criticism against the New Zealand study referred to last night on the CBC’s the National.

“Mr. Earleywine notes that Mr. Fergusson and his colleagues did not actually diagnose psychosis in the marijuana smokers they studied. Instead, they administered a short mental health questionnaire that asked if the respondent had ever experienced any of 10 "psychotic symptoms."

Some symptoms are clearly troubling, such as "hearing voices that other people do not hear" and having "the idea that someone else can control your thoughts." Others are not so obviously strange: feeling that other people cannot be trusted; feeling that you are being watched or talked about by others; never feeling close to a person; and having ideas and beliefs that others do not share.

Among 25-year-olds who had never smoked marijuana, the mean number of symptoms reported was 0.64. That number rose among those who smoked marijuana: Less-than-monthly users reported 0.89 symptoms, while daily marijuana smokers reported 1.95 symptoms. That rise, modest though it may be, is statistically significant.

But Mr. Earleywine believes there might be less here than meets the eye. In a letter to be published in the journal that published the study, Mr. Earleywine notes that it is fairly common for marijuana intoxication to cause feelings of paranoia, but the researchers "give no indication that respondents were asked to distinguish between feelings experienced while intoxicated and feelings experienced at other times. Thus, we are left with no clue as to whether these are long-term effects actually indicative of mental illness or simply the normal, passing effects of acute intoxication."
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"Fourteen years ago, the treating physician at the King/Drew Medical Center incorrectly believed that he was treating a patient having an acute asthma attack. He had several phone conversations with one of our physicians. Neither physician discussed the possibility that the child was suffering from a grave blood infection. During the course of those conversations, given the asthma misdiagnosis, the Kaiser physician believed that necessary tests could be conducted at Kaiser once the child was stabilized for asthma and transported to Kaiser. As a result of the misdiagnosis, the child ultimately succumbed to her blood infection. We offer our deepest sympathy to her family. ….

We regret that none of the physicians involved recognized that the child had a life-threatening infection and not asthma. The movie claims we denied coverage of treatment by the doctor at the county hospital. That was not true. The issue was a misdiagnosis followed by the wrong treatment. The movie is inaccurate in its portrayal of that sad case.

This was essentially a tragic case of medical malpractice.”

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