According to the results of research published in The American Journal of Psychiatry, nearly one-third of patients with diagnoses of substance-induced psychosis were later diagnosed with bipolar or schizophrenia-spectrum disorders.
To evaluate the rates of conversion to schizophrenia and bipolar disorder following diagnosis of substance-induced psychosis, researchers evaluated 6788 participants from a Danish database who were diagnosed with substance-induced psychosis between 1994 and 2014. Participants were matched with 67,227 controls. The participants were monitored until the first occurrence of bipolar disorder or schizophrenia or until death, emigration, or August 2014. The cumulative probabilities of development of schizophrenia or bipolar disorder were evaluated with the Kaplan-Meier method to obtain cumulative probabilities; hazard ratios (HR) for covariates were calculated with Cox proportional hazards regression models.
A total of 26.0% of participants were diagnosed with schizophrenia and 8.4% were diagnosed with bipolar disorder within 20 years after their diagnosis of substance-induced psychosis. Participants with cannabis-induced psychosis had the highest conversion rate to schizophrenia (41.2%; 95% CI, 36.6-46.2).
Relative to comparators, participants with substance-induced psychosis were at elevated risk for conversion to schizophrenia (HR 77.3; 95% CI, 65.2-91.7; P <.001) and bipolar disorder (HR 24.4; 95% CI, 20.1-29.6; P <.001). Among the different causes of substance-induced psychosis, cannabis-induced psychosis was associated with the highest risk for schizophrenia developing (HR 101.7; 95% CI, 74.1-139.7; P <.001), and sedative-induced psychosis was associated with the highest risk for bipolar disorder (HR 33.0; 95% CI, 6.9-159.0; P <.001).
Participants who were age 16 to 25 years were at an increased risk for disease conversion to schizophrenia, with decreasing risk associated with increasing age. In contrast, age did not appear to have an impact on the risk for bipolar disorder. Men had a higher risk for disease conversion to schizophrenia but a lower risk for disease conversion to bipolar disorder compared with women. Substance use disorder, personality disorder, and eating disorders were associated with increased risk for disease conversion to schizophrenia. In contrast, personality disorder, unipolar depression, and anxiety disorders were associated with increased risk for disease conversion to bipolar disorder.
In total, 32.2% (95% CI=29.7-34.9) of patients with substance-induced psychosis had disease conversion to bipolar disorder or schizophrenia. Half of the cases of conversion to bipolar disorder occurred within 4.4 years, and half of the cases of conversion to schizophrenia occurred within 3.1 years.
The study authors concluded that the results, “suggest that all patients with a substance-induced psychosis should be offered follow-up. Since only 50% of the cases that convert from cannabis-induced psychosis to schizophrenia do so within the first 2 years, and the rate of conversions over time is lower for all other substances and for conversion to other diagnoses, the follow-up period should be at least 2 years.”
Starzer MSK, Nordentoft M, Hjorthøj C. Rates and predictors of conversion to schizophrenia or bipolar disorder following substance-induced psychosis [published online November 28, 2017]. Am J Psychiatry. doi:10.1176/appi.ajp.2017.17020223