Cannabis and Schizophrenia: The Current Debates

Researchers are losing their heads over the cannabis and schizophrenia debate. Beginning with the 1930s boom in anti-marijuana campaigns, cannabis consumption has long been associated with psychotic behavior.

Yet, the correlation between cannabis and psychosis is highly controversial. On one hand, several studies have linked cannabis consumption to an increase in mental illness in young people. On the other, it’s difficult to tell whether or not cannabis is causing mental illness, or acts as a crutch for people who are already prone to psychotic tendencies.  

In order to clear up some of the debate, here are some of the recent studies cannabis consumers should know about:

The Harvard Study, 2013 

A recent Harvard University study divided a total of 282 participants into four groups:

1. People who have never used cannabis and do not have a history of psychosis
2. People who have used cannabis frequently and do not have a history of psychosis
3. People who do not use cannabis and have a history of psychosis
4. People who frequently use cannabis and also have a history of psychosis. 

The study then asked each participant to disclose whether or not their first, second, and third-degree relatives had a history of schizophrenia or psychosis. This is the first and only study that has collected data from four differing groups of people as well as tracked family history of mental illness. 

What researchers found was the exact opposite of what the general population seems to expect: there was no correlation between cannabis consumption and likelihood of mental illness in family groups. The authors of the report even made a point of explaining, “while cannabis may have an effect on the age of onset for schizophrenia, it is unlikely to be the cause of illness.” 

The Time Magazine Report, 2013

This December, Time Magazine published an article that directly contradicted the Harvard Study cited above. In a discussion of a recent Schizophrenia Bulletin study, author Alexandra Sifferlin summarizes the study, explaining that researchers believe cannabis may cause long-term brain changes similar to those found in schizophrenia patients.

The study looked exclusively at teens between 16 and 17 years old, and also split participants into four groups:

1. Those who have used cannabis
2. Those who have not used cannabis
3. Schizophrenia patients who are cannabis consumers
4. Schizophrenia patients who are not cannabis consumers. 

After performing a series of MRI tests, scientists found that those who have consumed marijuana have shrinkages in the areas of the brain which are responsible for memory. This difference allowed healthy non-cannabis users to score 37 times higher on memory tests than cannabis consumers. Schizophrenic participants who were non-cannabis consuming scored four times higher than their cannabis using counterparts. 

So, what does memory have to do with risk of schizophrenia? The answer to that question is mysteriously missing in the article, but both the researchers and Sifferlin were quick to articulate that the study in no way suggests that cannabis use actually causes psychosis.

The Schizophrenia Bulletin Studies, 2012

Whether or not cannabis causes schizophrenia is debatable, but can cannabis help psychotic patients? This article published by the Schizophrenia Bulletin examines two separate studies. The first study was actually a meta-analysis of 10 different studies, which looked at 572 schizophrenia patients who both have and have not used cannabis. 

The second study looked closely at 85 patients who have had one psychotic episode and tested their neuropsychological performance. For an oversimplified definition, an examination of neuropsychological performance refers to an examination of their motor, cognitive, and behavioral abilities. As always, study participants were separated in to two groups: cannabis users and non-cannabis users.

When analyzing both studies, researchers found that cannabis users actually had better cognitive functioning when compared to non-users, meaning patients who already had a history of psychosis and also consumed cannabis generally performed better and had higher neuropsychological functioning than patients who do not use cannabis.

But, what about cannabis improves mental abilities? The researchers are not sure. In the discussion of the study results, researchers were quick to explain that this study in no way refutes the argument that cannabis itself may cause psychosis, especially in young consumers. However, it may be a helpful treatment for those who already suffer from mental illness. 

These mixed results paint an inconclusive picture when it comes to cannabis and schizophrenia. Rather than allowing investigations of how the most commonly used illicit substance affects the brain, most cannabis research will be halted by government gatekeepers. For now, we’re left with the slow trickle of studies on schizophrenia and cannabis, all of which should be read with a careful eye and a grain of salt.

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