Cannabis-induced psychosis is associated with the highest conversion rate to schizophrenia or bipolar disorder (47,4%).
Summary
n=6.788 patients with substance-induced psychosis (Danish registry 1994–2014); 32.2% (95%-CI 29.7–34.9%) converted to schizophrenia spectrum or bipolar disorder. Highest conversion rate for cannabis-induced psychosis: 47.4% (95%-CI 42.7–52.3%). Half of all conversions to schizophrenia within 3.1 years; young age and self-harm as significant risk predictors. Published in American Journal of Psychiatry.
P
PopulationPersons with diagnosis of substance-induced psychosis (Denmark, 1994–2014), n=6.788
I
InterventionCannabis-induced psychosis (as well as other substance-induced psychoses) as exposure variable
O
Outcome32,2% (95% CI=29,7–34,9) converted to schizophrenia or bipolar disorder; highest rate for cannabis-induced psychosis: 47,4% (95% CI=42,7–52,3)
Confidence in the evidence
Very lowLowModerateHigh
Low
The second of four GRADE levels, the effect estimate is of limited reliability.
Design: Nationale Registerstudie (Dänemark, Kaplan-Meier + Cox-Regression)
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Abstract
The authors investigated the rates of conversion to schizophrenia and bipolar disorder after a substance-induced psychosis, as well as risk factors for conversion. All patient information was extracted from the Danish Civil Registration System and the Psychiatric Central Research Register. The study population included all persons who received a diagnosis of substance-induced psychosis between 1994 and 2014 (N=6,788); patients were followed until first occurrence of schizophrenia or bipolar disorder or until death, emigration, or August 2014. The Kaplan-Meier method was used to obtain cumulative probabilities for the conversion from a substance-induced psychosis to schizophrenia or bipolar disorder. Cox proportional hazards regression models were used to calculate hazard ratios for all covariates. Overall, 32.2% (95% CI=29.7-34.9) of patients with a substance-induced psychosis converted to either bipolar or schizophrenia-spectrum disorders. The highest conversion rate was found for cannabis-induced psychosis, with 47.4% (95% CI=42.7-52.3) converting to either schizophrenia or bipolar disorder. Young age was associated with a higher risk of converting to schizophrenia. Self-harm after a substance-induced psychosis was significantly linked to a higher risk of converting to both schizophrenia and bipolar disorder. Half the cases of conversion to schizophrenia occurred within 3.1 years after a substance-induced psychosis, and half the cases of conversion to bipolar disorder occurred within 4.4 years. Substance-induced psychosis is strongly associated with the development of severe mental illness, and a long follow-up period is needed to identify the majority of cases.