Cannabis is the most widely used drug across the world – second only to nicotine and alcohol.
With the legalization of cannabis expanding rapidly, it’s important to understand its effects on mental health – more specifically, its relationship to the schizophrenia syndrome warrants our attention.
Although cannabis has long been identified as a hallucinogen because of the acute and transient perceptual changes it tends to induce, this has been considered controversial. In fact, little evidence exists to support cannabis-induced hallucinations.
However, delusions resulting from cannabis use are much more common and cannabis has been directly linked to paranoia and persecutory ideation. While this has been observed during the acute intoxication effects of cannabis, the same dichotomy between hallucinations and delusions may also be applicable to long-term effects.
Regular cannabis use and psychotic disorders, including schizophrenia, have been connected in the general population.
Heavy cannabis users are found in higher rates among new cases of schizophrenia. Coupled with increasing rates of cannabis use (some legal), and rising use particularly among young adults, this has prompted debates about whether cannabis use contributes to the onset of psychosis.
Research has yet to identify a causal relationship between cannabis use and schizophrenia, however, several hypotheses are considered likely in explaining the link. Research has namely identified three explanations for their connection:
- Cannabis use has the potential to trigger schizophrenia in users who would not have developed the illness if they were not exposed to the drug.
Studies have found that any exposure to cannabis increased risk of psychotic outcomes by approximately 1.5 times when compared to non-users. In a study published in 2019, daily cannabis users were found to have increased their risk of developing psychosis by more than three times compared to controls that had never used cannabis.
Dose and frequency of cannabis use has been researched widely and continues to be reliable indicators in predicting the onset of psychosis. There is some evidence to suggest that cannabis consumed in higher frequencies increases risk of psychosis. Cannabis exposure at younger ages, as well as more potent variants of cannabis with higher THC and lower cannabidol (CBD) concentrations has been found to exacerbate the risk of developing psychosis.
In a 2009 study, first-episode psychosis patients were more likely to be current cannabis users or to have used cannabis for longer than 5 years, in comparison to a healthy control group, suggesting a potential bidirectional relationship between cannabis and psychosis.
- Individuals with a genetic predisposition to psychotic disorders use cannabis to self medicate early symptoms of psychosis.
One to two thirds of people with psychosis begin using cannabis after their first psychotic episode.
It is believed that some cannabis users use cannabis to mediate the negative symptoms associated with schizophrenia (such as social withdrawal, poor motivation and reduced emotional responses and speech). This might add credibility to new research that has shown cannabidiols to provide therapeutic value in treating schizophrenia.
- Other common factors contribute to the relationship, such as childhood trauma or genetics.
Genetic studies have widely explored shared genetic liability as a link between cannabis and schizophrenia. To date, genetic research has yet to provide an explanation connecting a single gene or biological factors that can identify a clear direction of the relationship between cannabis and schizophrenia. While it’s possible there is a potentially causal relationship, genetic vulnerability would be significantly influenced by an individual’s environment – such as exposure to trauma.
Numerous studies have investigated the influence of childhood trauma on the relationships between cannabis use and risk of psychosis. Dose and frequency of cannabis use continue to be reliable indicators when considering the risk of developing psychosis, which may be exacerbated by environmental factors or guided by experiences of childhood trauma.
Regular cannabis use promotes an increased risk of schizophrenia, even when controlling for other variables.
While there is no direct causal link between cannabis and psychosis there is a minimum link connecting the two. Regular cannabis users are at double the risk of developing psychosis and this onset of psychosis is earlier in young people, as the adolescent brain responds to cannabis differently compared to the adult brain. High potency cannabis with high levels of THC further intensify this risk.
Whilst further research needs to be conducted to investigate a causative relationship between cannabis and psychosis, at the very minimum cannabis has been found to be a risk factor (neither necessary nor sufficient) in causing psychosis. This is believed to interplay with genetic background and environmental factors.
Author: Tara Pisano, BA (Psych) (Hons), M Psych.
Tara Pisano is a Brisbane psychologist with a special interest in early intervention in adolescents and young adults, as this is when three quarters of mental health conditions emerge. In her practice, she draws on a range of evidence-based therapies such as CBT, DBT, IPT, ACT and Motivational Interviewing, to promote recovery and positive outcomes.
To make an appointment with Tara Pisano, try Online Booking. Alternatively, you can call M1 Psychology Loganholme on (07) 3067 9129 or Vision Psychology Wishart on (07) 3088 5422.
- Di Forti, M., Quattrone, D., Freeman, T. P., Tripoli, G., Gayer-Anderson, C., Quigley, H., Rodriguez, V., Jongsma, H. E., Ferraro, L., La Cascia, C., La Barbera, D., Tarricone, I., Berardi, D., Szöke, A., Arango, C., Tortelli, A., Velthorst, E., Bernardo, M., Del-Ben, C. M., Menezes, P. R. (2019). The contribution of cannabis use to variation in the incidence of psychotic disorder across Europe (EU-GEI): a multicentre case-control study. The lancet. Psychiatry, 6(5), 427–436. https://doi.org/10.1016/S2215-0366(19)30048-3
- Legge, S. E., Jones, H. J., Kendall, K. M., Pardiñas, A. F., Menzies, G., Bracher-Smith, M., Escott-Price, V., Rees, E., Davis, K., Hotopf, M., Savage, J. E., Posthuma, D., Holmans, P., Kirov, G., Owen, M. J., O’Donovan, M. C., Zammit, S., & Walters, J. (2019). Association of Genetic Liability to Psychotic Experiences With Neuropsychotic Disorders and Traits. JAMA psychiatry, 76(12), 1256–1265. https://doi.org/10.1001/jamapsychiatry.2019.250
- Patel, S., Khan, S., M, S., & Hamid, P. (2020). The Association Between Cannabis Use and Schizophrenia: Causative or Curative? A Systematic Review. Cureus, 12(7), e9309. https://doi.org/10.7759/cureus.9309
- Van der Steur, S. J., Batalla, A., & Bossong, M. G. (2020). Factors Moderating the Association between Cannabis Use and Psychosis Risk: A Systematic Review. Brain Sciences, 10(2), 97. http://dx.doi.org/10.3390/brainsci10020097
- Wainberg, M., Jacobs, G.R., di Forti, M., & Tripathy, S. J. (2021). Cannabis, schizophrenia genetic risk, and psychotic experiences: a cross-sectional study of 109,308 participants from the UK Biobank. Translational Psychiatry, 11, 211. https://doi.org/10.1038/s41398-021-01330-w