Medical marijuana and schizophrenia

Schizophrenia is a very complex mental syndrome that affects a person’s emotional, social, and cognitive behaviour. It is estimated to affect around 1.1% of the world population over the age of 18. That is roughly 51 million people around the globe.

Cannabis has been the focus of a growing body of scientific research, with many studies exploring the medical potential of the plant and its compounds. Some of these studies have shown that cannabis may help alleviate the symptoms of mental conditions like anxiety and depression. But what does science say about the relationship between cannabis and schizophrenia?


Schizophrenia is a complex medical disorder characterized by disturbances to a person's behaviour, emotions, thought process, and more.

Schizophrenia is often portrayed in media and popular culture, such as movies and television series. In these representations, schizophrenia is usually characterized by extreme symptoms like outbursts of violent behaviour and split personalities. While these symptoms can affect some patients, they don’t paint a very accurate picture of schizophrenia in general.

It is important to understand that every patient’s experience with schizophrenia is different. The disorder can manifest itself in a wide variety of ways, and can produce many different symptoms.


Schizophrenia is characterized by a wide variety of symptoms. These symptoms are usually divided into 3 separate categories:

Positive symptoms

These symptoms encompass psychotic-like behaviours which usually aren’t observed in healthy people. They can best be described as symptoms that cause a patient to lose touch with reality. Positive symptoms usually respond well to medication. Some common examples of positive symptoms include:

  • Hallucinations
  • Delusions
  • Unusual or illogical ways of thinking
  • Movement disorders (agitated body movements, for example)
Negative symptoms

These symptoms usually affect a patient's emotions and behaviour. They are usually thought of emotional and behavioural deficits that aren’t expressed in healthy people. Unlike positive symptoms, negative symptoms usually prove difficult to treat with medication. Some examples of negative symptoms include:

  • Reduced expression of emotions, both via facial expressions and the tone of voice (often referred to as the “flat affect”)
  • Reduced feelings of pleasure and a reduced capacity to get pleasure from pleasurable activities
  • Difficulty beginning and finishing activities or tasks
  • Reduced speaking
Cognitive symptoms

The cognitive symptoms of schizophrenia, also known as disorganized symptoms, usually interrupt a patient's thought process. These symptoms may be subtle or very severe, depending on the patient. Some examples of cognitive symptoms include:

  • Poor executive functioning (reduced ability to understand information and use it to make decisions)
  • Difficulty focusing
  • Poor working memory (the ability to use information immediately after learning it)


In order to be diagnosed with schizophrenia, a patient must have at least 2 of the following symptoms:

  • Hallucinations
  • Delusions
  • Disorganized speech
  • Disorganized behaviour
  • Negative symptoms

Note: To be diagnosed with schizophrenia, 1 of those symptoms needs to be either hallucinations, delusions, or disorganized speech. The diagnosed symptoms also have to be ongoing for at least 6 months.


The exact causes of schizophrenia are unknown. However, a number of factors are believed to increase the risk of developing schizophrenia. These include:

  • Genetics. Some sources suggest that genetics play a big role in the development and prevalence of schizophrenia. Children with 1 schizophrenic parent, for example, have roughly a 15% increased risk of developing the syndrome themselves. Children with 2 schizophrenic parents, on the other hand, are up to 40% more likely to develop schizophrenia.
  • Chemical imbalances. Antipsychotic medications that can help manage the symptoms of schizophrenia block dopamine receptors in the brain, ultimately reducing dopamine levels in neurons. This suggests that schizophrenia may be linked to increased levels of dopamine in the brain.
  • Brain development. Studies of people with schizophrenia have shown that patients may have subtle structural differences in their brains. These changes aren’t unique to schizophrenic patients, however, and not all people with schizophrenia have these structural differences.
  • Pregnancy and birth complications. Some resources have noted that low birth weight, premature birth, and asphyxia during birth can be linked to schizophrenia. It could be that these factors have an impact on later brain development.
  • Drug abuse. The abuse of drugs is common among patients with schizophrenia, but its isn’t clear whether drug abuse can cause the syndrome. However, some sources suggest the use of psychoactive drugs may increase the risk of developing schizophrenia in patients that are already at risk.


The relationship between cannabis and schizophrenia is complex. There is a variety of research that suggests cannabis use is associated with the development of psychosis and schizophrenia. How exactly cannabis use affects the development of schizophrenia, however, isn’t clear.

We know that cannabis interacts with the human endocannabinoid system (or ECS), which is involved in neurotransmission and reward processing, as well as the regulation of sleep, mood, cognition, and more.

Patients with schizophrenia have been shown to have elevated levels of endogenous cannabinoids like anandamide in the blood and cerebrospinal fluid. Studies have also shown that schizophrenic patients have higher amounts of cannabis receptors in the brain. This suggests that the endocannabinoid system and both endogenous and non-endogenous cannabinoids play an important role in schizophrenia.

One of the first landmark studies examining the relationship between cannabis and schizophrenia was published in 1987. It was authored by researchers from the Department of Social Medicine at the Karolinska Institutet in Huddinge, Sweden.

Based on 15-year follow-up data from over 45,000 Swedish participants, the study found that the risk of schizophrenia was considerably high among cannabis users. Even after adjusting for other factors like other psychiatric illnesses and social backgrounds, the authors of the study concluded that cannabis use “is an independent risk factor for schizophrenia.”

An analysis of a smaller subsample of participants in this study (conducted by the same authors in 1989) supported these results. Another paper, published by the same authors in 1993 but based on other medical records, also concluded that there was a strong relationship between cannabis use and an increased risk of schizophrenia.

More recent research has produced similar results. In 2008, for example, researchers conducted nationwide research across Denmark to examine the relationship between a familial predisposition to schizophrenia and cannabis-induced psychosis. The research showed that patients with a schizophrenic family member were more at-risk of developing cannabis-induced psychosis.

The study also showed that over 50% of patients treated for cannabis-induced psychosis went on to develop schizophrenia in the next 9 years. This risk, however, was independent of familial predisposition.

One of the most important factors involved in the relationship between cannabis use, schizophrenia, and psychotic disorders, is age of onset. A growing body of research suggests that young people with a disposition for mental disorders should not consume cannabis.

Many other studies have noted a relationship between cannabis use and psychosis as well as schizophrenia. For more information on these individual studies, we suggest reading this 2009 review of clinical studies on the topic.


Plenty of research shows that cannabis use is extremely common among patients with schizophrenia and psychotic disorders. Why schizophrenic and psychotic patients use cannabis, however, isn’t so clear.

It is unclear how THC, the main psychoactive compound in cannabis, affects schizophrenic patients. Obviously, it’s psychoactive properties make both healthy and schizophrenic patients feel “high.” The characteristics of that high, however, can be different for schizophrenic patients.

Research suggests that the compounds in cannabis might produce positive effects in some patients, encouraging them to “self-medicate” with the drug. However, some studies also suggest that schizophrenic patients may experience heightened positive and negative symptoms when under the influence of the drug. Other studies also argue that cannabis may relieve symptoms temporarily, followed by worse episodes once the effects of the drug wear off.

This makes sense, seeing that THC triggers a heightened release of dopamine. As we saw earlier, some successful antipsychotic medications work by suppressing dopamine in the brain.

However, it is important to realise that THC isn’t the only compound found in cannabis. As we know, another major constituent of the plant is cannabidiol, or CBD, which happens to have substantial antipsychotic potential.

In 2012, researchers from the Department of Neuroscience and Behavior, Faculty of Medicine, University of São Paulo and National Institute for Translational Medicine published a comprehensive review of the antipsychotic properties of CBD, and suggest the compound may play a key role in the treatment of psychosis in the future.

CBD, THC and other cannabinoids found in the cannabis plant have received a lot attention lately for their use in treating and managing the symptoms of mental disorders.

Unfortunately, there is a general consensus THC may enhance the symptoms of schizophrenia and psychosis, and that patients suffering from these conditions should refrain from using cannabis, at least for the time being.

Note: We have taken the utmost care and precaution whilst writing this article. That being said, please take note of the fact that we are not medical professionals of any kind. is strictly a news and information website. This content is not intended to be a substitute for professional medical advice, diagnosis, or treatment.