The Link Between Marijuana, Psychosis, and Schizophrenia: Alarming or Exaggerated? | Center on Addiction

The Link Between Marijuana, Psychosis, and Schizophrenia: Alarming or Exaggerated?

The Link Between Marijuana, Psychosis, and Schizophrenia: Alarming or Exaggerated?


In the past few years, marijuana has become more widely available and its use more accepted. Twenty-five states and Washington D.C. have now legalized it in some form. Still, concerns remain about marijuana’s effects. One growing but not well-recognized health problem is that marijuana can induce psychosis – particularly when the marijuana ingested is highly potent or when the individual is susceptible to developing psychotic disorders such as schizophrenia.

Schizophrenia is just one type of psychotic disorder and it is one of the most chronic, severe, and debilitating forms of mental illness. Like marijuana-induced psychosis, its symptoms include paranoia, delusions and hallucinations. Distinguishing between schizophrenia symptoms and a marijuana-induced psychosis is sometimes difficult, but the differences are significant. Schizophrenia is usually diagnosed in young adulthood, and generally results in permanent and pervasive disability. Marijuana-induced psychosis is typically temporary and less severe, and the prognosis for a full recovery is much better.

Can marijuana really cause schizophrenia?

A number of studies, both new and old, establish a connection between the timing of the onset of schizophrenia and marijuana use. Yet whether marijuana use can actually cause this illness is less clear. While marijuana use has increased recently, as has its potency, the number of individuals diagnosed with schizophrenia in the past few years has remained constant (at about 1 percent).

According to Dr. Nora Volkow, the Director of the National Institute on Drug Abuse at the National Institutes of Health, individuals with schizophrenia are at greater risk of marijuana use because they tend to self-medicate their developing or existing symptoms with marijuana. She states that even though marijuana is in reality making these symptoms worse, many individuals with early symptoms of schizophrenia believe that it helps them cope with the uneasy feelings typical of the disorder. She says that while marijuana can bring on psychotic symptoms, it does not seem that its use is actually causing schizophrenia.

Yet others believe that marijuana use isn’t a form of self-medication for those with schizophrenia – but is the cause of the schizophrenia itself. In one study, which looked at data over many years, researchers found that marijuana use significantly contributed to schizophrenia, even when other major factors that are usually thought to lead to schizophrenia (like family history of the disorder and other drug use) were considered. These researchers suggest that the biological interaction between the chemicals in marijuana and certain chemicals in the brain could potentially cause the illness.

The Dramatic Impact of Marijuana on the Adolescent Brain

While marijuana use doesn’t appear to be the primary cause of severe mental illness, it can still have a damaging impact on adolescent brains, as well as speed up the onset of psychotic disorders in those who are susceptible. Researchers have shown the many ways in which marijuana affects the brain, and how those who use marijuana regularly, particularly young people, are at higher risk of mental health problems. In fact, it’s widely accepted that the damage from adolescent marijuana use can have profound and long-lasting effects on their developing brains.  

Even for otherwise healthy individuals, using marijuana at a young age (13-24 years old) contributes to the loss of the cortical lining – the protective lining in the brain. This “cortical thinning” can have dramatic consequences, impairing attention, memory, and the ability to process the visual world.

It has yet to be proven that cortical thinning is directly related to schizophrenia or other forms of psychosis. Nonetheless, for individuals at high risk for schizophrenia, or who already are diagnosed with it, marijuana use clearly makes symptoms worse. One study showed that cortical thinning was greater in the first five years of using marijuana among those with schizophrenia compared with healthy individuals who used marijuana. For individuals with or at risk for schizophrenia – whose brain functioning is already impaired – marijuana’s damage is, in effect, compounding the problem.

Why Does it Matter? 

Though marijuana-induced psychosis usually has temporary effects, it still poses a danger to young people, especially if they are vulnerable to developing a psychotic illness. One study found that individuals who used marijuana regularly at age 18 were six times more likely to develop schizophrenia as adults.

Adolescents with early symptoms of schizophrenia face even greater risks from marijuana use, especially since they and their caregivers are often unaware that these symptoms indicate schizophrenia; rather, the symptoms are frequently misinterpreted as depression. Additionally, adolescents with a predisposition for schizophrenia who use marijuana develop their illness more quickly, and tend to have poorer outcomes.

The cost to young lives experiencing or vulnerable to severe mental illness is tremendous. There must be a more concerted effort to educate the public, and young people especially, about the particularly serious risks to mental health posed by regular marijuana use.

 Max Dorfman, MA

Max is a Science Writer at Center on Addiction


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