Experts answer top questions about marijuana and potential risks for schizophrenia and psychosis (a potential symptom of schizophrenia).
Marijuana (also termed cannabis in this article) use has become increasingly more accepted in the United States, as people in several states have voted to legalise the drug for recreational or medical purposes. In 2021, the U.S. Department of Health and Human Services National Survey on Drug Use and Health researchers estimated that 36.4 million people reported using marijuana within the previous month.
Some short and long-term health risks of marijuana use have been established, but researchers still have many unanswered questions about the connection between marijuana and schizophrenia, including whether marijuana could cause schizophrenia.
Below, experts answer the top questions you may have about what the risks might be, as well as what experts still don’t know for certain.
Can Marijuana Cause Psychosis?
Yes, research has shown that marijuana can cause psychosis, says David Streem, MD, a psychiatrist at Cleveland Clinic in Ohio. “Regular cannabis users have double the risk of developing psychosis, from 0.07 to 0.14 percent. It’s one of the few consistent findings in recent cannabis research,” says Dr. Streem, referencing prior research published in the journal Archives of General Psychiatry.
Symptoms of psychosis are common among people with schizophrenia and can include delusions (steadfast false beliefs) and hallucinations (seeing or hearing things that others don’t see or hear). A person experiencing a psychotic episode may also experience paranoia, uneasiness with others, trouble sleeping, social withdrawal, and difficulty functioning, among other symptoms, according to the National Institute of Mental Health.
The risk for psychosis is likely to increase as the potency of THC in cannabis increases, says Streem.
THC, which stands for delta-9-tetrahydrocannabinol, is the major psychoactive component of the marijuana plant and causes the euphoria or “high” that many people feel after using the drug.
It’s also important to note that marijuana is much more potent nowadays than it was several decades ago. According to research published in April 2016 in the journal Biological Psychiatry, the level of THC has tripled, rising from approximately 4 percent in 1995 to 12 percent in 2014, making the effects much stronger.
Does Heavy Marijuana Use Increase Risk of Developing Schizophrenia?
It’s hard to say with certainty that marijuana use directly leads to schizophrenia because of the limitations of available research. It doesn’t look at causation, but rather association, says J. Michael Bostwick, MD, a psychiatrist at Mayo Clinic in Rochester, Minnesota.
What’s more, research has not yet confirmed if other factors may be at play in the relationship between marijuana and schizophrenia risk, such as whether there might be prodromal symptoms of schizophrenia (meaning symptoms that come before an illness) that make someone more likely to use marijuana.
In other words, there is evidence that links marijuana use with an increased risk of psychiatric disorders, including schizophrenia, says Streem, but it’s still unclear if marijuana use actually causes schizophrenia.
“A 2002 study found the more marijuana an adult consumed, the higher their risk of developing schizophrenia,” Streem says, referencing research published in the journal BMJ.
“The authors concluded that 13 percent of the schizophrenia cases in their cohort could be attributed to smoking cannabis.”
Another study, published in the journal Schizophrenia Bulletin, showed that patients who use cannabis regularly and experience a first episode of psychosis could improve their prognosis if they quit using cannabis, states Streem.
Another study showed that emergency room visits for substance-induced psychosis were associated with an increased risk for developing schizophrenia. It also showed that those with substance-induced psychosis who used cannabis in particular, had the highest risk for transitioning to schizophrenia.
Can a Person’s Genetics Influence the Risks Related to Marijuana Use and Schizophrenia?
Research published in the journal Schizophrenia Research looked at people who used marijuana who did or did not have a family history of schizophrenia, and compared them with people without a family history who did or did not use the drug.
They found an increased risk of developing schizophrenia for the people with a family history of the condition, regardless of whether they had used marijuana.
Researchers concluded that marijuana doesn’t cause schizophrenia by itself, but it may initiate the onset of schizophrenia in people who are genetically predisposed to the condition.
“If you have psychotic illness in your family then you might want to be especially careful,” says Dr. Bostwick. “If you have a tendency to the illness yourself, using marijuana could bring the illness out sooner and more intensely,” he says.
Does Marijuana Impact the Same Part of the Brain That Relates to Schizophrenia?
Cannabis causes massive releases of many neurochemicals (brain chemicals), which makes it very difficult to know what all the effects may be, says Streem.
Bostwick agrees that there are still too many unknowns, both in the disease as well as the drug effects, to be able to pinpoint the chemicals or part of the brain affected, or to make this assertion.
One way to think about the relationship between schizophrenia and marijuana use is to look at the symptoms or behaviours of each, he says.
“If you already have a tendency toward psychosis or paranoia due to one illness, and then you start using a substance that has a tendency toward psychosis or paranoia on top of that, then you have a double effect thing going on,” he says.
Summary
Research has shown that marijuana use can cause psychosis, especially with prolonged use or higher doses of THC. Marijuana is also linked to an increased risk for schizophrenia, though experts don’t yet know whether marijuana use actually causes schizophrenia. The risks for psychosis, schizophrenia, or other health problems are especially significant among teens (particularly boys and young men ages 16 to 20), and most experts recommend against teen marijuana use in general.
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