Can Marijuana Create a Predisposition to Schizophrenia?

by Linda on April 20, 2012

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Marijuana Use and Schizophrenia

Marijuana Use and Schizophrenia Linked?

There has been much debate about the pros and cons of medicinal marijuana use. The arguments on each side tend to be extreme and may not clearly reflect the ambiguity related to marijuana’s legalization.

People who advocate the legalization of marijuana cite that marijuana has been shown to help cancer patients deal with the side effects of chemotherapy. It may also increase the appetites of those suffering from specific medical conditions.

However, very little data exists that provides researchers with a definitive answer as to whether or not there is a link between marijuana use and schizophrenia. There is evidence that links marijuana use with the onset of an acute psychotic episode, which has led to some researchers to assert that there is a direct link between marijuana use and schizophrenia or other psychoses. For example, findings of two long-term studies revealed that early cannabis use indicates a higher risk of psychosis. This may be especially true in adolescents, who are in a sensitive period of neurodevelopment.

In a recently published article, “The Cannabis-Psychosis Link,” published online in January 2012 by Psychiatric Times, researchers reviewed data addressing the “disagreement and uncertainty surrounding the nature of the interaction between cannabis and psychotic disorders.” These researchers stated that cannabis use is greater among patients who are schizophrenic than in the general public and that 25% of patients with schizoaffective disorder have used cannabis. Findings of two long term studies revealed that early cannabis use indicates a higher risk of psychosis. Adolescents, these researchers wrote, are at a sensitive period of neurodevelopment.

This article, however, does not solve the uncertainty surrounding the issue of schizophrenia and marijuana use. Some studies have found that patients with schizophrenia who used cannabis experienced an increase in psychotic symptoms, but other studies have not been able to verify these findings.  Furthermore, there are still more issues yet to be explored that remain problematic in formulating a clear, concise answer to the question such as: the level of CBD in cannabis, the level of THC in cannabis, and the level or presence of any of the other 400 chemicals or over 60 cannabinoids in a cannabis plant. Also, other studies have only begun to examine the impact of a first episode of psychosis and long-term psychological outcomes depending upon continued marijuana use and discontinuing marijuana use.

(Source: Marie-Josee Lynch, et. al., (2012) Cannabis-Psychosis Link, Journal of PsychiatricTimes, retrieved from )

The results of other meta-analysis studies have found that those who suffered the onset of psychosis who used cannabis as adolescents and young adults were 2.7 years younger than nonusers when their first episode occurred.

A 2011 study published in the Archives of General Psychiatry determined that alcohol use was not a significant factor in earlier age onset of psychosis, though other studies have included alcohol and other drugs within their research parameters.

(Source: Arch Gen Psychiatry. 2011;68(6):555-561. doi:10.1001/archgenpsychiatry.2011.5, retrieved

In a third major study, researchers examined marijuana use before the first episode of psychosis and its correlation with continued use and cessation of use. This study found data indicating a negative impact on disorder state and functioning with those who continued use.

To our knowledge, this is the first study that has measured long-term functional outcome while controlling for use of alcohol and other drugs and in which those patients who are able to stop using cannabis are separated from those who cannot do so. In the only previous study that separated patients with recent-onset psychosis into groups based on duration of cannabis use, the patients who continued to use cannabis over the 4-year follow-up had a more chronic course of disease… In addition, those patients who used cannabis but stopped using it during follow-up had fewer negative symptoms, although the difference was not significant… Furthermore, in a group of children and adolescents with a first psychotic episode followed up for 6 months, quitting cannabis was associated with a better outcome… Other studies evaluating functional outcome in patients with a first psychotic episode and continued use of cannabis generally found a worse outcome in such patients…

Source: Schizophrenia Bulletin vol. 37 no. 3 pp. 631–639, 2011 doi:10.1093/schbul/sbp126, retrieved from

Given the uncertainty about marijuana precipitating a psychotic disorder, researchers argue that screenings, psych education and early interventions are prudent, especially for those who are vulnerable, either through environmental or genetic risk, to psychosis.