Does Cannabis Really Cause Psychosis?

You may have read about a study that seemed to make an alarming link between cannabis and psychosis. The study claimed that in some cities, 30–50% of first-episode psychosis could be prevented if people didn’t have access to highly potent cannabis.

These are scary numbers. And plenty of media outlets picked up the story with reefer madness-like headlines of scientists finally proving that cannabis causes psychosis.


Well, don’t write off cannabis. While the study is important, its findings are far more complicated than the headlines suggest. And let’s be clear: If you’re consuming cannabis, you’re not likely to suffer from psychosis as a result.

Let’s take a look at this issue, and find out what all of the controversy is about.

Study Finds a Correlation Between Marijuana & Psychosis

The study that’s been causing so much controversy analyzed data from 901 patients across 11 cities in Europe and Brazil. These folks were admitted to psychiatric services with first-episode psychosis between May 2010 and April 2015. Researchers compared this population to a control group of about 1,200 people from the same cities, and asked each group about their habits, including their marijuana consumption.

What the study found was a correlation between cannabis consumption and psychosis. The researchers discovered that those who consumed cannabis daily were three times more likely to develop psychosis.

Meanwhile, those who smoked high-potency cannabis—which the researchers defined as marijuana containing at least 10% tetrahydrocannabinol (THC)—were twice as likely to develop psychosis. This rate went up to four times as likely for those who smoked high-potency cannabis daily.

In cities where high-potency cannabis was most widely available, such as London and Amsterdam, researchers also found higher rates of psychosis. Using statistical analysis, they went so far as to say that if high-potency cannabis weren’t available in these cities, then the number of first-episode psychosis cases would drop by about 30% in London and 50% in Amsterdam.

They also estimated that across all 11 cities, about 12% of psychosis cases could be prevented if high-potency cannabis wasn’t available.

Does This Study Prove That Cannabis Causes Psychosis? The Answer Is No

These findings sound pretty damning, and of course, they need to be taken seriously. However, they also need to be taken with a large grain of salt.

What the study proves is that there’s a correlation between marijuana consumption and psychosis.

But it in no way proves that cannabis causes psychosis.

This distinction is key, as other factors could also show that people who are predisposed to psychosis are also more likely to consume cannabis. There are several common factors that could help explain both an elevated risk of psychosis and a tendency towards heavy cannabis consumption, like:

  • Diet
  • Lifestyle factors
  • Genetics
  • Upbringing

For example, a separate study found that people with schizophrenia are more likely to take cannabis. This is because frequent cannabis consumers and people with schizophrenia have a genetic overlap. This genetic overlap increases the likelihood of schizophrenia and the likelihood of cannabis consumption.

But what it doesn’t do is show that taking cannabis increases the risk of schizophrenia.


To show causation requires much more extensive research. As psychiatrist and addiction researcher at Columbia University, Dr. Diana Martinez, flatly states, “You can’t say that cannabis causes psychosis. It’s simply not supported by the data.”

Determining whether cannabis causes psychosis would require:

  • Following participants over time
  • Collecting genetic information
  • Ideally, comparing twins

Psychosis is extremely complicated, and saying that cannabis causes it isn’t a claim that’s backed up by the evidence.

Another limitation with the study is that it focused on people who were daily consumers of high-potency cannabis. In fact, most studies that have found a link between the plant and psychosis have focused on this group of cannabis consumers.

But daily cannabis consumers aren’t representative of those who partake in the plant overall. In fact, people who smoke cannabis daily make up only a fraction of overall cannabis consumers.

And again, it should be stressed that people more likely to suffer from psychosis may also be more prone to being daily cannabis consumers. Saying that one causes the other is a conclusion that the data just don’t support.

The Medical Benefits of Marijuana in Relieving Issues Accompanying Psychosis

Another issue that can get overlooked when a study links cannabis to psychosis is that marijuana also has a number of proven medical benefits. One reason that people who suffer from psychosis may be more likely to consume cannabis is because they may simply be using cannabis as a form of self-treatment.

Research has shown that marijuana can relieve many unpleasant disorders or problems, including insomnia, stress and depression—all things that people with psychosis are already at a higher risk of suffering from. (This isn’t to say that if you do suffer from psychosis, you should self-medicate with cannabis.)


Cannabis is certainly not a wonder drug that will cure every ailment. Like anything, it has side effects, and it may not be suitable for everyone.

Research pointing to a correlation between cannabis and psychosis is important. And more research is needed to understand what that link is.

But using this correlation to prohibit marijuana consumption—or keep the stigma around the plant alive—makes no sense. Alcohol abuse has been shown to cause psychosis, but few people are arguing that we need to ban alcohol or at the very least, stop drinking it.


Instead, we should try to keep things in perspective. As of yet, there’s little evidence that cannabis actually causes psychosis. Instead, there’s evidence that it has helped many people find relief from the symptoms that can accompany psychosis.

Photo credit: Fure/

If you’re new to cannabis and want to learn more, take a look at our Cannabis 101 index of articles. And if you have questions about cannabis, ask them and our community will answer.


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