We know there’s a link between cannabis and psychosis, a term that covers a set of related conditions involving symptoms such as various types of hallucinations and delusions. Schizophrenia is the most commonly referenced disorder where symptoms of hallucinations are a prerequisite for a diagnosis. 

Continue Reading Below

The Latest Research 

In July 2019, a new review by Current Psychiatry Reports was published that aimed to understand the relationship between cannabis and schizophrenia. “Three hypotheses have emerged as potential explanations for the association between cannabis and schizophrenia, namely:

  1. Cannabis can trigger schizophrenia, 
  2. Cannabis is used to mitigate symptoms of schizophrenia, and;
  3. There are common factors which might account for the association. 

The authors of the review analyze these hypotheses and concluded that “the evidence for cannabis acting as a causal factor for schizophrenia has so-far not been established.”

The Relationship Between Schizophrenia and Marijuana

As a patient and consumer it can be frustrating to read contradictory health information. Many wonder why after all these years there’s no conclusive evidence, despite the link between cannabis and schizophrenia being known for over a century?

What is known so far is that there are essentially three theories with respect to the relationship between cannabis and schizophrenia and the problem is trying to prove them experimentally.

  1. Cannabis can trigger schizophrenic symptoms in someone who wouldn’t have had them if they didn’t use the drug. 
  2. A person who already has schizophrenia symptoms might use cannabis as a way to lessen initial symptoms (prodromal symptoms).
  3. There could be genetic and environmental factors in the relationship between cannabis and schizophrenia. 

Theory #1

Trying to prove the first theory is difficult because the research involved requires observational studies which have serious limitations. For example, if dosage is considered a risk factor, the problem is that there is significant variability of “dose” in these studies. Some researchers use an “exposure that is 50 times or more . . . [while] others use last month's usage to indicate regular use.” Another problem is that cannabis metabolites can last for weeks in your system, which can lead to false positives.

Continue Reading Below

Theory #2

With regards to the second theory, apparently “pleasure and recreation” are the most common reasons cited by patients who are thought to be using cannabis to mitigate the early symptoms of schizophrenia. However, there is growing evidence that suggests cannabidiol (CBD) could reduce psychotic symptoms. This means it’s possible that schizophrenic individuals could be benefiting from self-medication. 

Theory #3

With respect to the third hypothesis, a “shared genetic liability” has been shown to be a link. According to the July 2019 report, “genetic research has failed to provide [an] explanation involving a purely biological or genetic factor that makes clear the direction of the relationship between cannabis and schizophrenia.” To make it even murkier, researchers can’t rule out a person's environment in all of this. A review of the research out there with respect to cannabis and schizophrenia demonstrates this confusion:

Older Research 

According to several cohort studies, where subjects are studied over time, the association between cannabis and psychosis often depends on how early someone begins using the substance, how potent it is and how often it’s used. A variety of other risk factors also come into play, such as whether someone’s parents have schizophrenia symptoms and whether subjects used multiple other drugs, such as alcohol or amphetamines.

schizophrenia risk factor table Schizophrenia Risk Factors by Australia's National Drug Strategy
Another review of the literature published in 2007 in World Psychiatry noted that people with psychosis, who regularly use cannabis, have more symptoms, more frequent relapses and require more hospitalization, and recommends that anyone with such symptoms stop using cannabis, or at least cut back.

CBD Reduces Schizophrenic Symptoms

As briefly mentioned above, CBD could reduce schizophrenic symptoms. A multicenter randomized clinical trial (December 2017) showed that administering 1000mg of cannabidiol (CBD) daily for 6 weeks alongside the currently prescribed antipsychotics led to improved functional outcomes in schizophrenia symptoms when compared to a placebo.

What is most intriguing about this new study is that CBD did not act by binding Dopamine receptors or affecting Dopamine (the target for current antipsychotic drugs) which potentially means a new class of treatment for this disorder. Another randomized clinical study demonstrated that when compared to a potent antipsychotic (amisulpride), CBD in fact showed similar effectiveness in clinical symptom improvement in schizophrenia patients. The advantage of using CBD was that patients experienced less side effects compared to amisulpride. 

Research on the horizon

So then the obvious question is what is the current state of affairs with respect to the investigations with regards to CBD’s properties? A review of the clinicaltrials.gov database, shows two active, but not yet recruiting, clinical trials that will assess the relationship between CBD and acute schizophrenia and early psychosis). Two trials have also been completed in assessing CBD in acute psychosis and in schizophrenia or schizophreniform disorder, but have no published results. 

What is Schizophrenia? 

Schizophrenia is a serious and seriously misunderstood disorder. It is not a single disease, but a term used to describe an array of chronic, unexplainable psychotic symptoms. The onset of schizophrenia typically occurs between ages 16 and 30, but it is possible (though rare) for children to develop the disorder as well. Schizophrenic symptoms include the following:

  • Delusions
  • Hallucinations
  • Agitated body movements
  • Unusual thinking 
  • Decreased emotional expression 
  • Decreased feelings of pleasure 
  • Decreased speaking and social engagement 
  • Reduced executive functioning 
  • Difficulty focusing
  • Difficulty completing tasks 
  • Compromised working memory