Cannabis Use and the Course of Schizophrenia: 10-year Follow-Up After First Hospitalization

Thumyat Noe ’23

Figure 1: Elevated levels of cannabis are often observed in schizophrenic individuals, prompting researchers to study its potential effects on the course of schizophrenia. 

The relationship between cannabis use and course of schizophrenia have been extensively studied by researchers, as increased consumption of cannabis is often observed in individuals with schizophrenia. For the most part, results of these studies have been inconclusive. Some studies have reported that cannabis use is associated with less severe negative symptoms of schizophrenia, while other studies have suggested that cannabis users tend to display more severe psychotic and depressive symptoms than nonusers. Although the results vary, there appears to be more evidence to support that cannabis use may worsen the course of schizophrenia, but the exact mechanism behind this effect is not understood clearly. The goal of this study, conducted by researchers at Stony Brook University, was to better understand why cannabis use may possibly worsen the course of schizophrenia by identifying specific characteristics of schizophrenia associated with cannabis use during the first ten years after the first admission for psychosis. 

A total of 675 participants were recruited from twelve psychiatric facilities in Suffolk County, New York state, but only 229 participants were chosen and gave informed consent to be part of this longitudinal study. Out of 229 participants, only 162 participants were able to provide complete data. Researchers recorded symptoms of psychosis and depression and usage of cannabis in interviews with participants during their first admission into psychiatric facilities, 6 months, 2 years, 4 years, and 10 years later their first admission. The results showed that on average, the risk of psychosis was two times higher for cannabis users than non-users. Furthermore, cannabis users had elevated levels of psychotic symptoms at four of the five assessments, suggesting that increase in psychotic symptom severity is associated with cannabis use which is consistent with previous findings. To be clear, individuals with schizophrenia who use cannabis are not more severely ill but rather suffer from more severe symptoms. 

The findings of this study are helpful in eventually identifying mechanisms by which exposure to cannabis may influence psychosis. Furthermore, the results could help psychiatrists determine the best behavioral and biological treatment interventions for patients with schizophrenia. However, the biology of cannabis still needs to be examined more closely as this study mostly focused on the effects of cannabis on the course of schizophrenia. 

Work(s) cited: 


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