Supposed Marijuana-Schizophrenia Link Not Strong, Mainstream Media Reports

Washington, DC: A two-month-old study that found that increased cannabis use by the public has not been followed by a proportional rise in diagnoses of schizophrenia or psychosis is finally receiving mainstream press coverage.

“A British study has cast doubt on the supposed link between cannabis use and schizophrenia,” the Australian Broadcasting Corporation reported this week in a wire story carried throughout United Kingdom and North America.

NORML had previously reported on the study’s findings, which initially appeared online on the website of the journal Schizophrenia Research, on July 2.

Investigators at the Keele University Medical School in Britain compared trends in marijuana use and incidences of schizophrenia in the United Kingdom from 1996 to 2005. Researchers reported that the “incidence and prevalence of schizophrenia and psychoses were either stable or declining” during this period, even the use of cannabis among the general population was rising.

“[T]he expected rise in diagnoses of schizophrenia and psychoses did not occur over a 10 year period,” authors concluded. “This study does not therefore support the specific causal link between cannabis use and incidence of psychotic disorders. … This concurs with other reports indicating that increases in population cannabis use have not been followed by increases in psychotic incidence.”

In 2007, media sources around the world reported that consuming cannabis boosted one’s risk of developing a psychotic illness later in life by “40 percent.”

Last month, Canadian government officials publicly alleged that marijuana users have a “seven-fold increase” in risk of developing schizophrenia.

For more information, please contact Paul Armentano, NORML Deputy Director, at: paul@norml.org. Full text of the study, “Assessing the impact of cannabis use trends in diagnosed schizophrenia in the United Kingdom from 1996 to 2005,” appears in Schizophrenia Research.