British Medical Journal Reports on Link Between Marijuana, Schizophrenia

The respected British Medical Journal recently published 3 studies which found an increased risk for the onset of schizophrenia among chronic marijuana smokers. There is cause for concern – chronic use of a variety of drugs, including alcohol, has been known to exacerbate the symptoms of schizophrenia – but it is very likely that media reports will sensationalize these studies without providing adequate perspective. In their definitive meta-analysis of marijuana research, authors Lynn Zimmer, Ph.D. and John P. Morgan, M.D. dedicated an entire chapter to the subject of marijuana and mental illness. From Marijuana Myths, Marijuana Facts:

"There is no convincing scientific evidence that marijuana causes psychological damage or mental illness in either teenagers or adults. Some marijuana users experience psychological distress following marijuana ingestion, which may include feelings of panic, anxiety, and paranoia. Such experiences can be frightening, but the effects are temporary. With very large doses, marijuana can cause temporary toxic psychosis. This occurs rarely, and almost always when marijuana is eaten rather than smoked. Marijuana does not cause profound changes in people's behavior."

Ethan Russo, M.D. notes that the issue of cannabis as causing mental illness has been debated for at least 1000 years, usually on the basis of hysteria and myths, such as that of the hashish-crazed assassins. The first serious survey of cannabis in schizophrenia was the Indian Hemp Drugs Commission in 1893-1894. Researchers scoured the country’s asylums for cases of cannabis psychosis and came up with a mere handful of cases where there was not some alternative explanation. Their conclusion was that cannabis did not cause permanent harm of this nature. The same conclusion that cannabis did not "cause permanent psychosis" was reached in the Panama Canal Zone studies in the 1920’s and the LaGuardia Commission report of 1944. More recently, the Institute of Medicine study in 1999 and the Canadian Senate Report in 2002 came to the same conclusion.

Blair Anderson of New Zealand’s Mild Greens issued a press release on the BMJ studies that points to the need for harm reduction. According to Anderson, the failure of researchers to note that cannabis users are persecuted by law is a glaring omission from the analyses published in the BMJ. Presumptions about the adverse affects of cannabis formed the basis for concern when New Zealand Parliament's Health Committee inquired into the Mental Health Effects of Cannabis in 1998. The committee reported that "the negative mental health impact of cannabis appears to have been overstated." Their report acknowledged that it was actually the climate of criminality which generates paranoia and anxiety: "Those who develop problems [with marijuana] are less likely to seek help because they use an illegal substance, and may spiral in alienation, anti-social behaviour, criminality, mental illness or violence." The inquiry suggested in conclusion that "if cannabis does cause harm to a small proportion of users then it is preferable that those people have good access to treatment without fear of stigmatisation and discrimination."