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Cannabis and Schizophrenia: Do THC and CBD Affect It Differently?

March 5, 2018
(agsandrew/iStock)
Story Highlights:

  • The brain goes through critical periods of development during childhood and adolescence, and exposure to THC during this time is an environmental risk factor for schizophrenia.
  • While some studies claim that cannabis use plays a causal role in schizophrenia development, it can’t be ruled out that those who are more likely to develop schizophrenia are simply more prone to use.
  • On its own, the effects of CBD on schizophrenia symptoms have been mixed. Some studies have shown CBD’s antipsychotic potential while others found no therapeutic link.
  • CBD also has promise in improving the difficult-to-treat negative symptoms and cognitive impairment found in schizophrenia patients.

In the push for cannabis legalization, the link between cannabis and schizophrenia sometimes enters the discussion. Many fear that cannabis increases risk for developing schizophrenia, while others declare its value in helping relieve symptoms of the condition. But what does the research say about the role of cannabis in developing—and potentially treating—schizophrenia? 

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What Is Schizophrenia?

Schizophrenia refers to a group of conditions in which brain function is so impaired that sufferers lose touch with reality. It affects over 7.5 million adults in the United States, usually starting in their early 20s for men and slightly later in life for women.

Traditional treatments do little to treat negative symptoms such as a flat emotional state, a struggle to feel pleasure, and a lack of motivation to engage socially.

Psychosis isn’t the only defining feature of schizophrenia. The condition is a complex syndrome characterized by a range of symptoms that fall into positive, negative, and cognitive categories. Positive symptoms are the delusions, hallucinations, and disorganized speech that characterize psychosis and are associated with losing touch from reality. Pharmaceutical treatments for schizophrenia, called antipsychotic medications, target these positive symptoms.

Traditional pharmaceutical treatments, though, do little to treat negative symptoms such as a flat emotional state, a struggle to feel pleasure, and a lack of motivation to engage socially. They also fail to improve cognitive deficits, often leaving patients with impaired attention, memory, and problem-solving abilities.

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The Schizophrenic Brain

Predicting who is going to develop schizophrenia is a challenge for health care providers as there are no clear structural brain changes that can be detected before symptoms arise. Instead, the development of schizophrenia begins with abnormal communication patterns between groups of brain cells.

The risk of experiencing psychotic episodes increases with THC dose.

The abnormal communication patterns found in schizophrenia present in multiple ways, but the most common are dysfunction in two types of brain chemical systems: glutamate and dopamine. These chemicals, also called neurotransmitters, are used by brain cells to communicate with one another by activating receptors on other brain cells.

Glutamate is one of the most common neurotransmitters in the brain, activating a variety of receptors, including NMDA receptors. Activating NMDA receptors is an important step in brain cells forming connections with one another, and they play a critical role in brain development, learning, and memory. Many individuals with schizophrenia have abnormally low NMDA receptor activity, which can impair brain development and cognitive performance. In some cases, it’s this low NMDA receptor activity that leads to the schizophrenia symptoms later in life.

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The other neurotransmitter commonly implicated in schizophrenia is dopamine. Schizophrenic brains typically exhibit abnormally high levels of activity in D2 dopamine receptors, which are found throughout the brain’s limbic system—the system that regulates our emotions and motivational states. Abnormally high D2 receptor activity can lead to a host of schizophrenia symptoms such as an impaired grasp of reality, emotional dysregulation, and weakened cognitive abilities. Antipsychotic medications work by blocking the activity of D2 receptors.

Cannabis and Schizophrenia Risk Factors

The abnormal connections between brain cells that cause schizophrenia symptoms are triggered by an interaction of genetic issues and environmental factors, such as childhood trauma or cannabis exposure. One genetic trait, on its own, is usually insufficient to cause schizophrenia, nor is an environmental factor like cannabis use on its own. Taken in concert, though, these factors can cause the risk of schizophrenia to spike.

CBD is thought to have antipsychotic effects, but the greatest evidence for its antipsychotic ability is through blocking THC-induced psychosis.

The brain goes through critical periods of development during childhood and adolescence. Exposure to THC, the high-inducing chemical in cannabis, during this time is a substantial environmental risk factor for schizophrenia. This risk stems from the importance of the endogenous cannabinoid system (ECS), specifically cannabinoid type I (CB1) receptors, in controlling how neurons connect and communicate with one another. Indeed, there is evidence that THC can cause psychotic episodes immediately after using cannabis, some of which can persist after the effects of THC and require clinical intervention. The risk of experiencing these psychotic episodes increases with THC dose.

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The association between cannabis and schizophrenia is well-established; it’s been estimated that 8% of worldwide cases of schizophrenia can be attributed to cannabis. It should be noted, however, that while some studies claim that cannabis use plays a causal role in schizophrenia development, it can’t be ruled out that those who are more likely to develop schizophrenia are simply more prone to use cannabis.

It’s also worth noting that the cannabinoid composition of cannabis is often not considered in these studies. What about other cannabis constituents like cannabidiol (CBD), which has been found to have some antipsychotic properties?

Why the THC Risk?

As noted, genetic factors alone aren’t sufficient to cause schizophrenia. But when THC hits the brain, it may act as an environmental trigger for the condition. Evidence that THC exacerbates the genetically-determined risk of psychosis is found in brain cell connections. THC activation of CB1 receptors reduces the brain chemical, glutamate, which in turn, reduces NMDA receptor activation (see above). When THC activates CB1 receptors, it impairs glutamate production, which in turn lowers activity among NMDA receptors, ramping up the risk for the onset of schizophrenia.

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THC exposure can also impact dopamine receptors like D2. When D2 receptor activation is elevated, the brain cells in the limbic system become overly sensitive. In a normal brain, CB1 receptors reduce this sensitivity and contribute to normal brain activity. However, too much THC can weaken the strength of CB1 receptors, leading to an overall elevation of dopamine levels, elevated D2 receptor activity, and the psychosis that can accompany it.

How Does CBD Affect Schizophrenia?

The non-intoxicating cannabinoid CBD is being considered as a treatment for schizophrenia. CBD is thought to have antipsychotic effects, but the greatest evidence for its antipsychotic ability is through blocking THC-induced psychosis. On its own, the effects of CBD on schizophrenia symptoms have been mixed. In one report, CBD did not improve psychotic symptoms in patients that responded poorly to traditional antipsychotic treatment. A larger study, though, found that CBD effectively reduced psychotic symptoms.

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CBD (cannabidiol): What does it do and how does it affect the brain & body?

CBD also has promise in improving the difficult-to-treat negative symptoms and cognitive impairment caused by schizophrenia. Studies in animals found that CBD improved some of the negative symptoms such as social interaction deficits and working memory deficits.

One significant benefit of CBD, should it prove to be an effective antipsychotic medication, is that it’s well-tolerated and has fewer side effects compared to traditional antipsychotics. For instance, CBD doesn’t impact food intake or weight gain which is a common adverse side effect of antipsychotic medications. More work is needed to hash out these variable effects in humans, but in the meantime, keep the potential risks of THC in mind if you’re at all concerned about cannabis’ effect on schizophrenia.

Josh Kaplan's Bio Image

Josh Kaplan

Josh Kaplan, Ph.D., is an Assistant Professor of Behavioral Neuroscience at Western Washington University. He is a passionate science writer, educator, and runs a laboratory that researches cannabis' developmental and therapeutic effects.

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  • Zane

    I know this isn’t about whether it should be legal or not, but.. It has way more benefits and less side effects as THC OR CBD compared to any other type of medicine. 🙄 I take this article as generally good news!

    • Rosa Noswal

      Cbd is legal in all 50 states and Canada

      • Knitmygrits

        Nope. Wrong about Canada. I live in Canada and you just can’t get it off the shelf. The federal government has a medical cannabis program that you can only be referred to by your family doctor. If your doctor is not cannabis friendly, you’re out of luck as the waiting list for a new family doc is almost 2 years long AND you must be a patient of your family doctor for no less than FIVE YEARS and they have to have been treating your condition for that long with traditional therapies. I know as I’m a patient with PTSD and along with my family doctor’s records of treatment, I had to ALSO have a diagnosis by a clinical psychiatrist BEFORE I could get the referral to the cannabis doctor and THAT’S for THC AND the CBD as in Canada, it’s STILL legally labelled Cannabis and is STILL labelled a narcotic under the Controlled Substances Act.

  • Scott Hubachek

    It can trigger a psychotic episode, but it’s only revealing what is already there. I have smoked with thousands of people, but there were a couple I wouldn’t smoke with, because it was obvious that they were a little off center to begin with.
    In the end, it’s not the plant itself that there is a problem with.
    My question is this, have they tested a strain like acdc, 20:1 cbd/thc, on possible schizophrenia?

    • Scooter Bell

      Very true, the other group I tend to avoid toking with is heavy(not light 🙂 drinkers. The emotions tend to go all over the place
      when combined with weed. Pretty weird.

  • Rhiannon McCarty

    I am 20 years old. At the age of 13 I was diagnosed with schizophrenia. They had me heavily medicated and we tried almost every antipsychotic medication with usually no result or if it did work, the side effects were so bad I couldn’t function. I was barely there. When I tried cannabis, that was the moment I knew I never would take those nasty poisons again. Speaking from experience marijuana HELPS.

    • Scooter Bell

      Rock on Rhiannon — keep toking! :]

  • Alexa Farrell

    For the love of science, I’ll share my personal story… I’ve been diagnosed many things in the past. Bipolar, schizoaffective, and BPD, just to name a few. I was forced to take meds at a psychiatric school, because I was barred from attending regular private or public schools. If you were a model student, you went up tiers and were given privelleges. The highest ranking was Community Leader. That was Me. A ‘role model’, ‘team leader’ etc. I even had a clinician doing psych research on me and writing a book, ecstatic over my drastic improvements. But unbeknownst to him and everybody, I had stopped taking the meds. I was just smoking pot.

    • Scooter Bell

      For the love of science, I’d also mention it to your doc! :] Super glad it helped, you’re a leader to me for reporting it! :]

      • Alexa Farrell

        Yeah, reporting something two decades too late 🤣 especially with it’s already legalized!

  • takes1toknow1

    My brother was diagnosed with bipolar and schizophrenia at the age of 26. He was taking medicine proscribed by the doctors and they made him seem blank. I purchased a bottle of cbd oil online and asked him to take the droplet 2x a day under he tongue. In a week he was more back to himself. He now vapes cbd oil and hes bipolar and schizophrenia have gone away. Once marijuana becomes legal through the U.S. government, I’m sure cbd will be the main source for all medicines.

  • Has there been a study on the effects on people of living in a police state that victimizes people with mental illness for their choice of medication.
    The drug war creates a high stress environment in our society but most especially for the people who are already suffering PTSD from whatever cause. The drug war is an attack on the ill. It actually works to force mental illness on the community.

    • Facksqwud © Clothing

      Someone have a link?
      I’m looking for this study.

  • Zoot

    It was from watching an interview with the great Dr. Grinspoon many years ago that I learned that rates of schizophrenia in the world didn’t go up when use of cannabis became more popular, thus it does not bring out latent schizophrenia.

    I am schizophrenic and THC, usually from sativas, helps to melt/“bake” my tense brain and nerves. I imagine that draws many of us to it.

  • Alan Gruskoff

    I can make this report. Once I grew a single marijuana plant from a seed. After I harvested it, I shared some with my girlfriend who then responded with “Which one of us are you talking to?”, evidencing her latent schizophrenia.

    • Zoot

      Schizophrenia is not multiple personality disorder.

    • nixnoutz

      You weren’t also using a strong psychedelic? Old style cough syrup? Must have been some strong weed. Or?

  • Schizophrenics also use alcohol at a higher rate then the rest of the population, yet researchers do not make the same connection as marijuana. This not only illustrates anti-marijuana bias, but also that these rates are higher because these people are self medicating.
    If marijuana CAUSES schizophrenic symptoms, why do these people continue to use it? It appears they would try it once, then be afraid of it for the rest of their lives. Their continued use of the plant proves it medicates their symptoms, and does not cause them.

  • Maja

    Biased article against cannabis.

  • Mero

    If someone has schizophrenia in their family, bad experience with smoking pot the one or two times tried as an adolescent, but otherwise just mild anxiety, do we know if CBD oil with trace THC would be risky to take for fear of triggering predisposition for schizophrenia?

  • Jennie Mele

    Have you ever felt sick to your stomach after taking CBD oil?