Cannabis and Psychosis



The prevalence of any population having a psychotic disorder is approximately 3.5%; additionally, the incidence of schizophrenia is ~1%.  Just as there are an infinite number studies on ways predicting psychotic disorders, there are an equal amount of studies attempting to reduce the number of cases among the population. Nevertheless, without any background in research methods, one may not know what to make of all these studies.

Before we start, the following is a fundamental review of some research methods used in science.

A longitudinal study is a study looking at a group of participants over a period. Longitudinal studies are good at identifying changes in a system over time. However, they are not good at establishing causation.

Experimental research another conventional method used in science establishes cause and effect. Unfortunately, many restrictions on cannabis prohibit most experimental studies on humans.

A meta-analysis is a form of research synthesis that takes a group of studies and uses statistics to increase the power of an outcome. One-way researchers use a meta-analysis is to increase the likely hood that a variable is affecting a change. A meta-analysis is only as good as the studies used in the analysis. Note, if studies examined in a meta-analysis are from longitudinal research, the reader should not disregard information when experimental research is missing. However, the reader should realize these shortfalls and take into consideration that there may be more than the examined variable affecting the outcome.

Tetrahydrocannabinol (THC) is the psychoactive component of cannabis. Significant one-time doses of THC can produce a temporary mild psychotic episode in healthy naive cannabis users. Very little is known about THC increasing the prevalence of psychotic disorders in the cannabis population. This article reviews recent finding involving cannabis and psychosis.

A widely cited meta-analysis found that regular cannabis users may have a two-fold increase in psychosis. Another analysis examining the early onset of psychosis found adolescent cannabis use increased the risk of psychosis late in life. However, the method of analysis from both studies consisted of longitudinal and population-based all of which does not establish causation. Moreover, the studies used did not set a starting point for comparisons. Without a baseline, researchers cannot ascertain if an individual with psychosis is attracted to cannabis use or does cannabis use increase the risk of psychosis.

People do not need cannabis to develop psychosis. However, cannabis may add to the development of psychosis in at-risk individuals. A journal article from the Current Opinion in Psychiatry revealed that adolescent and adults already at risk of psychosis increase their risk when using cannabis.

That does not mean cannabis does not benefit individuals diagnosed with psychosis or schizophrenia. In another meta-analysis, researchers observed that people diagnosed with schizophrenia who use cannabis function better cognitively than individuals with schizophrenia that do not use cannabis. The at-risk population should consult proper medical professionals about the hazards cannabis may contribute to their mental health and seek information on the proper use of cannabis.

The cannabinoid Cannabidiol (CBD) is known to counter the psychoactive effect of cannabis. Additionally, scientist found CBD to have the same effect and a superior safety profile compared to the standard ant-psychotic medication. Therefore, CBD may reduce psychotic episodes and may soon be a safe alternative to aggressive antipsychotic medication after more studies.

In closing, cannabis use may increase the risk of psychosis and schizophrenia by two-fold in the cannabis population. Meaning the risk of a psychotic disorder may increase from 3.50% to 7% or from 1% to 2% in schizophrenia. Nevertheless, researchers will need more experimental studies to prove further how cannabis affects psychosis.

Although cannabis increases the risk of psychosis in the at-risk population, when correctly used, cannabis improved cognition in people with schizophrenia. At-risk individuals should seek professional medical advice before starting cannabis.

CBD is shown to counter the psychoactive effect of THC. Recently CDB presented an improved safety profile compared to the standard ant-psychotic medication suggesting CBD may be a safer alternative. More studies will be needed using CBD as an alternative to conventional medication.

Lastly, cannabis is not as dangerous as many perceive, and it is not as safe as others argue; the truth will be found somewhere in the middle.


Bhattacharyya, S., Morrison, P. D., Fusar-Poli, P., Martin-Santos, R., Borgwardt, S., Winton-Brown, T., . . . McGuire, P. K. (2009). Opposite effects of Δ-9-tetrahydrocannabinol and cannabidiol on human brain function and psychopathology. Neuropsychopharmacology, 35, 764. Retrieved from

Di Forti, M., Morrison, P. D., Butt, A., & Murray, R. M. (2007). Cannabis use and psychiatric and cogitive disorders: The chicken or the egg? Current Opinion in Psychiatry, 20(3) Retrieved from

D’Souza, D. C., Perry, E., MacDougall, L., Ammerman, Y., Cooper, T., Wu, Y., . . . Krystal, J. H. (2004). The psychotomimetic effects of intravenous delta-9-tetrahydrocannabinol in healthy individuals: Implications for psychosis.Neuropsychopharmacology, 29, 1558. Retrieved from

Large, M., Sharma, S., Compton, M. T., Slade, T., & Nielssen, O. (2011). Cannabis use and earlier onset of psychosis: A systematic meta-analysis. Archives of General Psychiatry, 68(6), 555-561. Retrieved from

Leweke, F. M., Piomelli, D., Pahlisch, F., Muhl, D., Gerth, C. W., Hoyer, C., . . . Koethe, D. (2012). Cannabidiol enhances anandamide signaling and alleviates psychotic symptoms of schizophrenia. Translational Psychiatry, 2, e94. Retrieved from

Moore, T. H. M., Zammit, S., Lingford-Hughes, A., Barnes, T. R. E., Jones, P. B., Burke, M., & Lewis, G.Cannabis use and risk of psychotic or affective mental health outcomes: A systematic review. The Lancet, 370(9584), 319-328. doi:10.1016/S0140-6736(07)61162-3

Perala , J., Suvisaari, J., Saarni, S. I., & al, e. (2007). Lifetime prevalence of psychotic and bipolar i disorders in a general population. Archives of General Psychiatry, 64(1), 19-28. Retrieved from

Yucel, M., Bora, E., Lubman, D. I., Solowij, N., Brewer, W. J., Cotton, S. M., . . . Pantelis, C. (2012). The impact of cannabis use on cognitive functioning in patients with schizophrenia: A meta-analysis of existing findings and new data in a first-episode sample. Schizophrenia Bulletin, 38(2), 316-330. Retrieved from