Can cannabis cause psychosis?: Investigating potential health risks of recreational cannabis use

By Hannah Rasiuk

person holding grey tongs and kush

Image description: A cannabis retailer employee weighs cannabis flowers on a scale. Image retrieved from Unsplash (2016).  

Amidst the ongoing closures of local businesses during COVID-19, many residents have noticed an explosion of new cannabis shops opening in Toronto neighbourhoods.1 As plans have been revealed to license 80 new Ontario cannabis retailers per month, the drug is becoming increasingly accessible.1 Given that cannabis has become the most widely used mind-altering drug among North Americans,2 Torontonians likely make choices about personal cannabis use on a regular basis. However, common misconceptions about cannabis may create difficulty in making informed decisions about recreational use. 

Cannabis is often thought of as a harmless substance and tends to be used by individuals to help with medical issues, without concern for its addictiveness.3 In reality, approximately 1 in 3 people who use the drug develop issues with their use, with 1 in 11 people developing the addiction, cannabis use disorder.4 Alongside being addictive, cannabis use may actually pose major risks to personal health.5 For example, research studies have been finding a connection between cannabis use and psychosis. An important part of understanding this relationship involves answering the question: does cannabis use actually cause psychosis to develop. The following discussion will unpack what psychosis is, as well as the research on this relationship in order to figure out if cannabis use could realistically cause psychosis, and how this might occur.

What is psychosis? 

Psychosis is a term used to describe personal problems and disruptions in mental functioning that results in people having difficulty staying in touch with reality. People experiencing psychosis have distressing changes in their normal beliefs, thoughts, behaviours, and ways of perceiving the world around them. The term can be used to describe the broad range of symptoms associated with psychosis, as well as to mental diagnoses that involve psychosis. For instance, schizophrenia is a well known psychotic disorder.6,7

Infographic by Hannah Rasiuk, template from CANVA is licensed under a CC BY-NC-ND 2.0., information retrieved from Schizophrenia Society of Canada (n.d.).

What are the symptoms of psychosis? 

Psychosis can look different among people who are experiencing it and can develop quickly, or gradually over time. The complex symptoms that individuals with psychosis may experience are listed below:

  • Hallucinations, which may involve perceiving sounds or visions that are not actually occurring
  • A loss of the sense that one’s experiences are, in fact, their own personal experiences 
  • Difficulty beginning tasks 
  • Reduced range of emotions and speech
  • Disorganized thoughts, speech, or behaviour (this could include issues in completing daily tasks, or fast and confusing changes in subject matter when speaking). 
  • Decreases in motivation 
  • Spending more time alone and neglecting social relationships
  • Issues with developing original ideas and thoughts
  • Delusions, which involve strongly held beliefs that may be bizarre or unrealistic.6,7

Can psychosis be caught early on? 

Although psychosis causes widespread negative effects on daily functioning, health, and well-being, it is a treatable condition.5 Treatments for psychosis commonly involve the use of medication, as well as psychotherapy. Antipsychotics are the main medication used to manage psychotic symptoms, and prevent symptoms in the future. Psychotherapy is useful for improving daily functioning and managing living with psychosis. Since psychosis is more easily treated when caught early on in its development,7 these symptoms may be important to look out for. Some early warning signs for the development of psychosis include:

  • Difficulty in completing normal self-care and hygiene practices
  • Decline in performance at work or school
  • Difficulty communicating with others
  • Adopting new ideas that may seem bizarre or intense
  • New issues in critical thinking and concentration 
  • Feeling suspicious of others
  • Spending an atypical amount of time by oneself
  • Trouble separating fantasy from reality.9 

Infographic by Hannah Rasiuk, template from CANVA is licensed under a CC BY-NC-ND 2.0., information retrieved from CAMH (n.d.a).

What has research shown about the associations between cannabis use and psychosis? 

The development of psychotic disorders is complex. There are many factors that may cause psychosis, including imbalances of chemicals in the brain, as well as stressful life events. If drug use does play a role in its development, it can only partially explain its cause.7 

Researchers believe that cannabis use may lead to psychosis by negatively affecting processes occurring in the brain. THC, also known as tetrahydrocannabinol, is the main ingredient in cannabis that creates changes in the brain that produce the ‘high’ feeling associated with use.10 Research suggests that THC interacts with chemicals in the brain that interrupt the brain’s ability to function normally. THC has effects on certain areas of the brain’s ‘reward circuit’, and affects the functioning of parts of the brain associated with critical thinking, mood, and meeting goals.11 These changes in the brain may be reflected by the issues in thinking, attention, or memory that individuals often experience shortly after using cannabis. Studies have also shown that people with psychosis also have similar abnormalities and issues in these areas of the brain, which contributes to their psychotic symptoms. Given this overlap, researchers suggest that these disruptions in the brain caused by THC could potentially contribute to the development of psychosis.11,12 

Research that focuses on individuals experiencing psychosis highlights how cannabis use may be linked to psychosis. Some of these findings include:

  • Psychosis patients who use cannabis have been found to develop psychosis at younger ages. Cannabis users in one study were found to have developed psychosis 6 years earlier than non-users, on average.13 
  • Cannabis use has been found to cause ‘acute’ episodes of psychosis. An acute episode of psychosis happens when psychosis-like symptoms develop immediately after using cannabis. These symptoms may extend beyond the time that the individual is intoxicated and may come before a full psychotic episode.5
  • Very few individuals who have already experienced psychosis report that they started using cannabis after their psychosis began.14 
  • Cannabis is the most commonly used mind-altering drug among individuals with schizophrenia. Within a study of patients with schizophrenia, 25% of patients had also received cannabis use disorder diagnoses.15
  •  Some studies have shown that psychosis patients using cannabis are readmitted to hospitals more often than those who do not use the drug.16 
  • 37% of psychosis patients in a study shared with researchers that their first psychotic symptoms began while intoxicated from cannabis.17 

Who might be vulnerable to developing psychosis after using cannabis? 

Certain individuals are more likely to develop psychosis when using cannabis than others. The age at which individuals begin to use cannabis, as well as a family history of psychosis have been shown to be particularly important in the relationship between cannabis use and psychosis. 

Did you begin smoking at a younger age?

Studies have demonstrated that participants who had used cannabis during teenage years had more psychotic symptoms, and were more likely to have schizophrenia later on in life.5 These results suggest that the teen years are an important and sensitive period of time for the brain’s development, and that cannabis use may negatively affect this development. For instance, a sample of psychosis patients who began using cannabis prior to the age of 16 developed psychosis at earlier ages than those who began using the drug after the age of 15.13 This highlights that using cannabis during adolescence, especially during early teenage years, may be particularly connected to the development of psychosis later on.

Do you have a family history of psychosis? 

Generally, individuals with a family history of psychosis are more likely to develop psychosis themselves.7 However, research suggests that cannabis use may uniquely increase the risk for developing psychosis among people with these genetic sensitivities.5 One study found that patients who were experiencing acute episodes of psychosis who had recently been using cannabis were 10 times more likely to report having a family history of psychosis, compared to patients who had not recently used cannabis.18 Among psychosis patients who use cannabis, it is common that family members who have experienced psychosis also use cannabis.19 

Other studies have identified that certain genes that are inherited from parents may uniquely contribute to the development of psychotic symptoms after using cannabis. Researchers have found that people who have specific variations of 2 genes, called AKt1 and COMT, have a greater likelihood of experiencing psychosis-like symptoms after using cannabis, as well as developing psychosis later on.5,19 These findings suggest that certain factors that are inherited from parents may allow some people to become particularly likely to develop psychosis after using cannabis. 

How might patterns of personal cannabis use increase the likelihood of developing psychosis? 

Certain patterns of cannabis use have been linked to the development of psychosis. Some relevant factors related to personal patterns include the frequency of cannabis use, as well as the strength, or potency of the cannabis used. 

Frequency of cannabis use

Many research studies have demonstrated that individuals who use cannabis on a daily basis have an increased likelihood of developing psychosis, including acute episodes of psychosis, compared to non-daily users.20,5 Researchers in one study found that patients experiencing their first episode of psychosis tended to smoke on a daily basis, smoke more frequently, and for longer periods of time.13 Another set of researchers who studied individuals over the course of 25 years also found that daily use was associated with up to 3.3 times more likely to develop psychosis compared to non-users.21 These results suggest that daily cannabis use over time may result in an individual being especially vulnerable to developing psychosis.

Potency of cannabis used 

High potency cannabis has higher amounts of THC.5 This means that higher potency cannabis is able to give users a more intense ‘high’ feeling after consuming smaller amounts, compared to low potency cannabis. High potency cannabis is also becoming more widely available at legal cannabis stores, with a 17% THC content considered to be ‘strong’ among Ontario cannabis retailers.22,23 Since cannabis retailers may not share information about the potency of their cannabis products, a guideline for this information is provided below:

Infographic by Hannah Rasiuk, template from CANVA is licensed under a CC BY-NC-ND 2.0., information retrieved from Government of Canada (n.d.b).

Numerous studies have found associations between higher potency cannabis and increased rates of psychosis.22 For instance, individuals experiencing their first episode of psychosis were found to have smoked higher potency cannabis at increased rates. The researchers in this study also found that potency was a factor that individually contributed to earlier onsets of psychosis among those who were studied.13 

Image description: Close-up shot of various types of higher-potency cannabis extracts displayed on a metal spatula. Image retrieved from Pixabay (2018).

How sure can we be about these findings?

There are some limitations to this research that make it unreasonable to conclude that there is a cause-and-effect relationship between cannabis use and psychosis. The research does suggest that cannabis use is a relevant factor among people with psychosis. However, it is unclear whether the people in these studies would have developed their psychosis anyway, without the use of cannabis. Similarly, not everyone who uses high potency cannabis on a daily basis will develop psychosis. It could also be possible that there are other undiscussed factors that allow certain people to be more at risk for both using cannabis, and for developing psychosis. It might be more reasonable to remain cautious in believing that cannabis use causes psychosis, and that it might just partially contribute to its development.21

How might these research findings be applied to everyday life?

Overall, these research findings connecting cannabis use to psychosis suggest that its reputation for being harmless may be unrealistic2. Evidence points to the idea that using high potency cannabis on a daily basis could contribute to the development of psychosis.5,13 If individuals have used cannabis since adolescence, and/or have a family history of psychosis, they may be especially vulnerable to developing psychotic symptoms. If the findings in these research studies were able to determine a cause-and-effect relationship between cannabis use and psychosis, they could be applied to daily life by changing patterns of personal cannabis use. In this case, people currently using cannabis should consider using cannabis with lower potencies, and avoid using it on a daily basis. 

Cannabis use disorder may be a barrier for those who are motivated to change these patterns of use2. Similarly to psychosis, cannabis use disorder is a treatable condition. Specifically, there is evidence that some psychotherapy options may be helpful for the treatment of cannabis use disorder.24 If additional personal support is helpful, readers are encouraged to access the online resources and information about healthcare services related to psychosis and addiction listed below. 

Resources for personal support available in Toronto:

GTA Mental Health Resources – Culturally Specific | Health & Counselling Centre

Connex Ontario: Mental Health & Addiction Treatment Services

Partners in Care: Supporting Families in Patient Recovery

To Access CAMH Services, call 416 535-8501, option 2.



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5Radhakrishnan, R., Wilkinson, S.T., & D’Souza, D.C. (2014). Gone to pot: A review of the association between cannabis and psychosis. Frontiers in Psychiatry, 5(54), 1-24. doi:10.3389/fpsyt.2014.00054

6Badcock, J., & Paulik, G. (2020). A clinical introduction to psychosis: Foundations for clinical psychologists and neuropsychologists. Elsevier.

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11Lutz, B. (2009). From molecular neurodevelopment to psychiatry: new insights in mechanisms underlying Cannabis-induced psychosis and schizophrenia. European Archives of Psychiatry and Clinical Neuroscience, 259(7), 369-370. doi:10.1007/s00406-009-0029-x

12Kuepper, R., Morrison, P.D., van Os, J., Murray, R.M., Kenis, G., & Henquet, C. (2010). Does dopamine mediate the psychosis-inducing effects of cannabis?: A review and integration of findings across disciplines. Schizophrenia Research, 121(1), 107-117.

13Di Forti, M., Sallis, H., Allegri, F., Trotta, A., Ferraro, L., Stilo, S.A., Marconi, A., La Cascia, C., Marques, T.R., Pariante, C., Dazzan, P., Mondelli, V., Paparelli, A., Kolliakou, A., Prata, D., Gaughran, F., David, A.S., Morgan, C., Stahl, D., … Murray, R.M. (2014). Daily use, especially of high-potency cannabis, drives the earlier onset of psychosis in cannabis users. Schizophrenia Bulletin, 40(6), 1509-1517. doi:10.1093/schbul/sbt181 

14Gonzalez-Pinto, A., Alberich, S., Barbeito, S., Gutierrez, M., Vega, P., Ibanez, B., Haider, M.K., Vieta, E., & Arango, C. (2009). Cannabis and first-episode psychosis: Different long-term outcomes depending on continued or discontinued use. Schizophrenia Bulletin, 37(3), 631-639.

15Rabin, R.A., Zakzanis, K.K., & George, T.P. (2011). The effects of cannabis use on neurocognition in schizophrenia: A meta-analysis. Schizophrenia Research, 128(1-3), 111-116.

16Colizzi, M., Burnett, N., Costa, R., De Agostini, M., Griffin, J., & Bhattacharyya, S. (2018). Longitudinal assessment of the effect of cannabis use on hospital readmission rates in early psychosis: A 6-year follow-up in an inpatient cohort. Psychiatry Research, 268, 381-387.

17Peters, B.D., de Koning, P., Dingemans, P., Becker, H., Linszen, D.H., & de Haan, Lieuwe. (2009). Subjective effects of cannabis before the first psychotic episode. Australian and New Zealand Journal of Psychiatry, 43(12). doi:10.3109/00048670903179095

18McGuire, P., Jones, P., Harvey, I., Williams, M., McGuffin, P., & Murray, R. (1995). Morbid risk of schizophrenia for relatives of patients with cannabis-associated psychosis. Schizophrenia Research, 15(3), 277-281. doi:10.1016/0920-9964(94)00053-B

19Murray, R.M., Quigley, H., Quattrone, D., Englund, A., & Di Forti, M. (2016). Traditional marijuana, high‐potency cannabis and synthetic cannabinoids: Increasing risk for psychosis. World Psychiatry, 15(3), 195-204. doi:10.1002/wps.20341

20Compton, M.T., Broussard, B., Ramsay, C.E., & Stewart, T. (2011). Pre-illness cannabis use and the early course of nonaffective psychotic disorders: Associations with premorbid functioning, the prodrome, and mode of onset of psychosis. Schizophrenia Research, 126(1), 71–76. doi:10.1016/j.schres.2010.10.005

21Fergusson D.M., Horwood. L.J., & Ridder, E.M. (2005). Tests of causal linkages between cannabis use and psychotic symptoms. Addiction, 100(5), 354-366. doi:10.1111/j.1360-0443.2005.01001.x

22Di Forti, M., Morgan., C., Dazzan, P., Pariante, C., Mondelli, V., Marques, T.R., Handley, R., Luzi, S., Russo, M., Paparelli, A., Butt, A., Stilo, S.A., Wiffen, S., Powell, J., & Murray, R.M. (2018). High-potency cannabis and the risk of psychosis. The British Journal of Psychiatry, 195(6). doi: 10.1192/bjp.bp.109.064220 

23Ontario Cannabis Store. (n.d.). Cannabis anatomy: What is thc?.

24Bobb, A.J., & Hill, K.P. (2014). Behavioral interventions and pharmacotherapies for cannabis use disorder. Current Treatment Options in Psychiatry, 1(2), 163-174. doi:10.1007/s40501-014-0013-6

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Unsplash. (2016). [Person holding grey tongs and kush] [Photograph].

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