Can Weed Cause Schizophrenia?
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Can Cannabis Cause Schizophrenia?

Experts answer top questions about weed and potential risks for schizophrenia and psychosis (a potential symptom of schizophrenia).
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Updated on November 27, 2024
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Pixellated marijuana leaf behind head silhouette
Marijuana can have a variety of effects on the brain.

Cannabis (marijuana) use has become increasingly more accepted in the United States: 38 states now allow the use of medical marijuana, and nearly half of U.S. states have voted to legalize its recreational use, too. Some short- and long-term health risks of marijuana have been established. But researchers still have many unanswered questions about the connection between cannabis and schizophrenia, including whether cannabis could increase the risk of schizophrenia.

We asked experts about the risks of cannabis use as well as what they still don’t know for certain.

What Causes Schizophrenia?

Psychiatrist Allison Young, MD, sheds light on some factors potentially linked to schizophrenia.
What Causes Schizophrenia?

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Can Weed Cause Psychosis?

According to David Streem, MD, a psychiatrist at the Cleveland Clinic in Ohio, cannabis use can cause psychosis, which is a symptom, not a disease in itself.

“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 cannabis research,” says Dr. Streem, referencing some prior research.

Symptoms of psychosis are common among people with schizophrenia. They can include delusions (unshakeable false beliefs, despite clear evidence that the beliefs are untrue) and hallucinations (seeing or hearing things that others don’t see or hear). If someone has a psychotic episode they may also experience the following symptoms:

  • Paranoia
  • Uneasiness with others
  • Trouble sleeping
  • Social withdrawal
  • Difficulty functioning

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 cannabis plant and causes the euphoria, or “high,” that many people feel after using weed.

It’s also important to note that cannabis is much more potent nowadays than it was several decades ago. According to research, the general potency of cannabis has increased from around 10 percent in 2009 to 14 percent in 2019.

Can Weed Cause Schizophrenia?

It’s hard to say with certainty that marijuana directly causes schizophrenia because of the limitations of available research. According to J. Michael Bostwick, MD, a psychiatrist at the Mayo Clinic in Rochester, Minnesota, currently available research focuses on association rather than causation.

What’s more, research has not yet confirmed if other factors may be at play in the relationship between cannabis 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 cannabis.

In other words, there is evidence that links cannabis use with an increased risk of psychiatric disorders (including schizophrenia), but it’s still unclear if weed use actually causes schizophrenia.

For instance, a prior 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 (the likely outcome of a disease) if they quit using cannabis.

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.

A systematic review that looked at data from 12 studies found that 10 of the studies supported a potential causal link between cannabis use and schizophrenia. However, the researchers noted that more studies are still needed to confirm this.

Weed Use Is Especially Risky for Teens

Cannabis use during adolescence appears to be a risk factor for developing schizophrenia at an earlier age and for more severe disease, one study suggests.

Research also suggests that having cannabis use disorder (meaning addiction to cannabis) is linked to an increased risk of schizophrenia, especially among boys and young men ages 16 to 20.

Along with increased risk of schizophrenia and psychosis, cannabis use is linked to several other short- and long-term risks among teens, according to the American Academy of Child and Adolescent Psychiatry (AACAP). They may include:

  • Problems at school
  • Memory and concentration issues
  • Increased aggression
  • Other drug or alcohol use
  • Car accidents
  • Risky sexual behavior
  • Mood changes or worsening of underlying mental health conditions
  • Cannabis use disorder
  • Similar respiratory problems that occur with smoking cigarettes
  • New mental health issues, such as depression, anxiety, moodiness, irritability, anger, or suicidal thoughts
That’s why many experts and organizations, including AACAP, recommend against recreational cannabis use among teens. There’s also very limited research supporting any benefits of medical marijuana use among teens for most conditions.

Can a Person’s Genetics Influence the Risks Related to Cannabis Use and Schizophrenia?

Prior research published in the journal Schizophrenia Research looked at people who used weed and who did or did not have a family history of schizophrenia. They compared them with people without a family history of cannabis usage who used cannabis themselves.

They found an increased risk of developing schizophrenia for the people with a family history of the condition, regardless of whether they had used cannabis or not. Researchers concluded that cannabis doesn’t cause schizophrenia by itself, but it may initiate the onset of schizophrenia in people who are genetically predisposed to the condition.

More recent research had similar findings. A large study published in Translational Psychiatry found that, while people who used marijuana in general had an increased risk for schizophrenia, this risk was especially pronounced in people who were genetically predisposed to schizophrenia.

“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 weed could bring the illness out sooner and more intensely,” he says.

Does Weed 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 cannabis use is to look at the symptoms or behaviors of each, he says. “If you already have a tendency toward psychosis or paranoia due to one illness and 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.

The Takeaway

  • Research has shown that marijuana can cause psychosis, especially with prolonged use or higher doses of THC.
  • Cannabis use is also linked to an increased risk for schizophrenia, though experts don’t yet know whether that can actually cause schizophrenia.
  • The risks for psychosis, schizophrenia, or other health problems are especially significant among teens who use cannabis (particularly boys and young men ages 16 to 20), and most experts recommend against teen cannabis use in general.

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Angela D. Harper, MD

Medical Reviewer
Castle Connolly Top Doctor

Angela D. Harper, MD, is in private practice at Columbia Psychiatric Associates in South Carolina, where she provides evaluations, medication management, and psychotherapy for adults.  

A distinguished fellow of the American Psychiatric Association, Dr. Harper has worked as a psychiatrist throughout her career, serving a large number of patients in various settings, including a psychiatric hospital on the inpatient psychiatric and addiction units, a community mental health center, and a 350-bed nursing home and rehab facility. She has provided legal case consultation for a number of attorneys.

Harper graduated magna cum laude from Furman University with a bachelor's degree and cum laude from the University of South Carolina School of Medicine, where she also completed her residency in adult psychiatry. During residency, she won numerous awards, including the Laughlin Fellowship from the American College of Psychiatrists, the Ginsberg Fellowship from the American Association of Directors of Psychiatric Residency Training, and resident of the year and resident medical student teacher of the year. She was also the member-in-training trustee to the American Psychiatric Association board of trustees during her last two years of residency training.

Harper volunteered for a five-year term on her medical school's admission committee, has given numerous presentations, and has taught medical students and residents. She currently supervises a nurse practitioner. She is passionate about volunteering for the state medical board's medical disciplinary commission, on which she has served since 2015.

She and her husband are avid travelers and have been to over 55 countries and territories.

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Becky Upham, MA

Becky Upham

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Becky Upham has worked throughout the health and wellness world for over 25 years. She's been a race director, a team recruiter for the Leukemia and Lymphoma Society, a salesperson for a major pharmaceutical company, a blogger for Moogfest, a communications manager for Mission Health, a fitness instructor, and a health coach.

Upham majored in English at the University of North Carolina and has a master's in English writing from Hollins University.

Upham enjoys teaching cycling classes, running, reading fiction, and making playlists.

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Resources
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