London, United Kingdom: Marijuana use is not associated with heightened symptoms of schizophrenia, according to data to be published in the journal Schizophrenia Research.
Investigators at London’s Institute of Psychiatry assessed whether the prior use of cannabis in patients with schizophrenia was associated with appreciable changes in schizophrenic symptoms compared with patients who had no history of marijuana use. Researchers performed logistic regression analysis on 757 volunteers with cases of first onset schizophrenia. Of these, 182 (24 percent) had reportedly used cannabis in the year prior to diagnosis, while 552 (73 percent) had not. (The remaining three percent had no data available.)
Investigators reported no statistically significant "differences in syptomatology between schizophrenic patients who were or were not cannabis users" after controlling for patients’ age, sex, and ethnicity.
Researchers also failed to find "any evidence that cannabis users with schizophrenia were more likely to have a family member with the disorder."
These findings "argue against a distinct schizophrenic-like psychosis caused by cannabis," authors concluded.
The study is the largest trial ever conducted to compare cannabis using and non-using schizophrenic patients, investigators said.
Although investigators did not assess whether cannabis consumers had greater odds of contracting schizophrenia compared to those who did not have a history of smoking pot, prior reviews have downplayed such an association. Most recently, Britain's Advisory Council on the Misuse of Drugs (ACMD) concluded in 2006, "For individuals, the current evidence suggests, at worst, that using cannabis increases lifetime risk of developing schizophrenia by one percent."
A separate 2006 report by Britain’s Beckley Foundation speculated that cannabis may "precipitate schizophrenia in people who are already vulnerable" to the disease, but it also acknowledged that the "increased rates of cannabis use in the last thirty years have not been accompanied by a corresponding increase in the rate of psychosis in the population."
NORML Advisory Board Member Mitch Earleywine, author of the book Understanding Marijuana: A New Look at the Scientific Evidence (Oxford University Press), said: "Schizophrenia is a rare and heterogenous disorder that requires both biological and environmental contributors. I hope this latest work helps to counter the idea that there exists a distinct psychotic disorder related to cannabis as well as other equally simplistic, and often inaccurate, notions regarding the use of cannabis and mental illness."
A study co-authored by Earleywine and published in the journal Psychiatry Research in 2005 reported that cannabis use typically follows rather than precedes behavior suggestive of schizophrenia. "These findings do not support a causal link between cannabis use and schizotypal traits," the study concluded.
For more information, please contact Paul Armentano, NORML Senior Policy Analyst, at: email@example.com. Full text of the study, "A comparison of symptoms and family history in schizophrenia with and without prior cannabis use: Implications for the concept of cannabis psychosis," will appear in the journal Schizophrenia Research. A discussion of this study may be downloaded from the May 2, 2007 edition of the NORML Daily AudioStash at: http://www.normlaudiostash.com. Additional information may be found in the NORML paper, "Cannabis, Mental Health and Context," available online at: http://www.norml.org/index.cfm?Group_ID=6798.