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What’s the Link Between Marijuana and Schizophrenia?
An image of brains related to schizophrenia.

Marijuana may play a role in the development of schizophrenia, but the evidence is inconclusive.

Many people have heard about a link between marijuana and schizophrenia. But does smoking marijuana really make you more likely to develop the disorder?

Compared to the average person, people with schizophrenia are more likely to be marijuana users. But it’s not known whether marijuana actually causes schizophrenia or if it’s just a correlation.

People who go on to develop schizophrenia may be more likely to try marijuana in the first place. And some studies even show that marijuana use may help treat some of the symptoms of schizophrenia.

Let’s look at both sides of the argument and uncover the whole picture.

What is Schizophrenia?

What is Schizophrenia?
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Schizophrenia is a chronic brain disorder. It can seriously impact the lives of people affected. Common symptoms include hallucinations, delusions, difficulty thinking clearly and lack of motivation.

In some cases, individuals will hear voices, become paranoid, or even lose the ability to move or speak.

There are many stereotypes about schizophrenia. But schizophrenia is not the same as a split personality. And most schizophrenics are not violent.

About 1 in every 100 people will develop schizophrenia during their lifetime, and the risk is similar for both men and women.

Researchers believe that genetics and environmental factors both play a role in the development of the disorder. There are treatment options available in the form of medication, but there is no cure.

Does Marijuana Cause Schizophrenia?

An image of someone smoking a marijuana joint
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It is highly unlikely that marijuana use alone causes schizophrenia. Schizophrenia is affected by genetics and other environmental factors, too.

Marijuana may play a part in developing the illness, though. People with schizophrenia tend to be current or former marijuana users. And using marijuana can trigger psychosis in some individuals.

But many scientists are skeptical of just how strong the link is between marijuana and schizophrenia.

Marijuana may contribute to developing schizophrenia

Fear about the link between marijuana and schizophrenia stems from a few major observations.

People with schizophrenia are more likely to have a history of cannabis use than the general population. And marijuana has been found to worsen psychosis in schizophrenia.

However, people with schizophrenia may simply be drawn to marijuana.

Marijuana can also cause psychotic symptoms, such as paranoia and hallucinations at very high doses. These symptoms are generally considered to be temporary and are not necessarily considered signs of mental illness.

Studies show that marijuana use only predicts the development of psychosis if people are heavily dependent on the drug.

People with schizophrenia are more likely to have a history of marijuana use, but scientists have yet to show whether marijuana can actually cause schizophrenia.

Dr. Matthew Hill, a professor and researcher at the University of Calgary, has explained why fear of marijuana causing psychosis may be overblown.

“Within the Western world, cannabis use went from essentially nonexistent in the 1950s to extremely prevalent in the 1960s and 1970s. Despite this dramatic shift in cannabis use at a societal level, the prevalence of schizophrenia has largely remained stable.”

One study explains that getting teens to quit smoking pot may not have much of an effect on rates of schizophrenia. The authors calculate that you would need to get 4000 teenagers to quit in order to prevent 1 case of schizophrenia.

Could Marijuana Treat Schizophrenia?

An image of marijuana in a pill bottle, indicating it's being used to treat schizophrenia.
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Some studies support the idea that marijuana may help with certain symptoms of schizophrenia. But there is also the possibility that it could worsen it.

People with schizophrenia may be more likely to use marijuana because it helps ease their symptoms. This theory could explain the link between marijuana and schizophrenia.

For example, studies have linked marijuana use to better cognitive performance among those with schizophrenia.

The relationship between schizophrenia and marijuana is complex. It seems that marijuana may help some aspects of the condition and worsen others.

THC vs. CBD

Whether marijuana helps or harms people with schizophrenia may be partly explained by the strain’s content of THC and CBD.

At high doses, THC may cause psychosis in healthy individuals. And it can worsen psychotic symptoms in people with schizophrenia.

This is a common argument made against the legalization of marijuana. And the fact that high-THC strains of cannabis are flooding the markets makes it even worse.

However, although THC can induce psychosis at high doses, the presence of CBD appears to counteract this effect.

CBD on its own shows promise as an effective treatment for schizophrenia. And it has fewer side effects than traditional medications.

Rather than rejecting marijuana entirely, it’s important to look at the effects of individual compounds.

Who Is Most at Risk?

Diverse people who may be at risk for schizophrenia.
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One point that experts agree on is that marijuana is not completely harmless. When it comes to the development of lifelong disorders, most agree that it is better to be cautious. This is especially true for those at high risk for developing schizophrenia.

Many factors can influence your risk of developing schizophrenia. These include genetic factors, starting marijuana use at a young age, frequent or heavy marijuana use, and the use of other drugs and alcohol.

Age

The brain undergoes many changes through the late teens and early 20’s. Using marijuana during this time can influence how the brain develops, and may increase the risk of developing schizophrenia. This is particularly true if usage is heavy.

Genetics

Genetics appears to play a major role in the development of schizophrenia. In other words, people who get schizophrenia already have genetic factors that predispose them to the illness.

Researchers also believe genetics plays a part in how likely you are to try marijuana. The exact genes that can predict schizophrenia and marijuana use haven’t been identified. But researchers are looking for common overlapping genes that could predict both.

Research to date has been very limited. But some reports suggest that having a risk of developing schizophrenia actually increases someone’s chances of trying marijuana, not that marijuana use increases the chances of developing schizophrenia.

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Heavy Use

People that smoke a lot of cannabis regularly — or are dependent on the drug — tend to have an increased risk of schizophrenia. Studies show that the effects of heavy use on psychosis remain even after 28 days of abstinence.

There is also a “dose-dependent” relationship between marijuana and schizophrenia. Some studies suggest that the more marijuana you smoke, the higher your chances of developing psychotic symptoms.

Use of Other Drugs

Using other drugs in addition to cannabis can further increase the risk for the development of schizophrenia. This can also worsen schizophrenic symptoms.

People with schizophrenia often suffer from a lack of motivation. Studies show that using marijuana and alcohol at the same time can further reduce motivation in this population.

People with schizophrenia are also more likely to smoke tobacco. It’s a common practice to ingest tobacco and marijuana together. But scientists warn against this combination, because it can worsen schizophrenia symptoms.

How Do I Know What Sources to Trust?

Skeptical woman questioning sources on marijuana and schizophrenia
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Debates about scientific matters can be confusing, but there are ways to navigate the discussion in order to stay safe and use marijuana responsibly.

Interpret scientific studies closely

There are many factors that can contribute to the development of schizophrenia. These factors include environmental toxins, an individual’s birth month and even growing up with cats.

Scientists cannot control these factors in real-world situations for practical and ethical purposes. So it is important to know that studies on the link between marijuana and schizophrenia come with limitations.

High-quality research is needed, and the National Academies of Sciences, Engineering and Medicine recognized this need in a joint report released in January 2017.

Know that it’s easy to twist evidence

Opinions on legalization can influence how risks and dangers are reported to the public.

There is evidence for marijuana use being both helpful and harmful when it comes to schizophrenia. So it’s possible to twist the evidence in favour of certain positions.

Marijuana certainly has the potential to increase the risk of psychotic disorders. But the strength of the effect, the role of strain composition and understanding who is at high risk are also important.

University of Calgary Professor Dr. Matthew Hill states: “the extreme opinions on the subject are not rooted in science.”

Use marijuana responsibly

With the current state of research, it is generally considered safer to:

  • Wait until after adolescence (18-25 years old) before using marijuana
  • Use marijuana in small doses and don’t consume too much at once
  • Pick strains that are lower in THC, and higher in CBD

Summary

People with schizophrenia are much more likely to be marijuana users or former users. This leads many people to believe that cannabis can cause schizophrenia.

But a direct link between marijuana use and the development of schizophrenia has yet to be proven. And in some cases, marijuana can actually treat symptoms of psychosis.

It’s important to read sources carefully and understand your risk for schizophrenia to make safer and more responsible decisions about marijuana use.

You can speak with your doctor to better understand the mental health risks and benefits of marijuana.

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