Marijuana Users at Risk for Early Psychosis
Records from more than 22,000 patients with psychotic illness reveals a link between marijuana use and early symptoms of psychosis. Psychotic illness occurs significantly earlier among marijuana users, results of a meta-analysis suggest.
Reducing the use of cannabis could be one of the few ways of altering the outcome of the illness because earlier onset of schizophrenia is associated with a worse prognosis and because other factors associated with age at onset, such as family history and sex, cannot be changed.
Psychosis has a strong association with substance use. Patients of mental health facilities have a high prevalence of substance use, which also is more common in patients with schizophrenia compared with the general population. Several birth cohort and population studies have suggested a potentially causal association between cannabis use and psychosis, and cannabis use has been linked to earlier onset of schizophrenia.
Attempts to confirm an earlier onset of psychosis among cannabis users have been complicated by individual studies' variation in methods used to examine the association.
On average, substance users were about 2 years younger than non users were. The effect of substance use on age at onset was greater in women than in men, but not significantly so. Heavy use was associated with earlier age at onset compared with light use and former use, but also not significantly different, the authors reported. Substance users were two years younger at the onset of psychosis compared with non users. Age at onset was 2.7 years earlier among cannabis users compared with non users.
Acknowledging limitations of the study, the authors cited the lack of information on tobacco use and its association with earlier age at onset of psychosis, and the lack of data on individual patients inherent in all meta-analysis.