Cannabis-induced psychosis is associated with a high risk of later schizophrenia-spectrum disorders and earlier first manifestation.
Summary
Prospective follow-up cohort (n=535) after cannabis-induced psychosis (Danish Psychiatric Register, 1994–1999, follow-up ≥3 years): 44,5% developed schizophrenia-spectrum disorders; 77,2% experienced new psychotic episodes of any kind. Schizophrenia occurred earlier than in the comparison group (men 24,6 vs. 30,7 years). Risk factors: male sex and young age.
P
PopulationPatients with first-time cannabis-induced psychosis without history of other psychotic disorders, n=535, Danish Psychiatric Register 1994–1999
ControlIndividuals with first-time schizophrenia-spectrum disorder without history of cannabis-induced psychosis
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Outcome44,5 % developed schizophrenia-spectrum disorders; 77,2 % experienced new psychotic episodes of any kind; male sex and young age were associated with increased risk; first diagnosis of schizophrenia occurred on average earlier than in the comparison group (men: 24,6 vs. 30,7 years, women: 28,9 vs. 33,1 years)
Confidence in the evidence
Very lowLowModerateHigh
Low
The second of four GRADE levels, the effect estimate is of limited reliability.
Quality profile
Sample size★★★★★
Blinding—
Effect sizeHarm
Citations / year★★★★★
Authors
Arendt M, Rosenberg R, Foldager L, Perto G, Munk-Jørgensen P.
<h4>Background</h4>Few studies have examined samples of people with cannabis-induced psychotic symptoms.<h4>Aims</h4>To establish whether cannabis-induced psychotic disorders are followed by development of persistent psychotic conditions, and the timing of their onset.<h4>Method</h4>Data on patients treated for cannabis-induced psychotic symptoms between 1994 and 1999 were extracted from the Danish Psychiatric Central Register. Those previously treated for any psychotic symptoms were excluded. The remaining 535 patients were followed for at least 3 years. In a separate analysis, the sample was compared with people referred for schizophrenia-spectrum disorders for the first time, but who had no history of cannabis-induced psychosis.<h4>Results</h4>Schizophrenia-spectrum disorders were diagnosed in 44.5% of the sample. New psychotic episodes of any type were diagnosed in 77.2%. Male gender and young age were associated with increased risk. Development of schizophrenia-spectrum disorders was often delayed, and 47.1% of patients received a diagnosis more than a year after seeking treatment for a cannabis-induced psychosis. The patients developed schizophrenia at an earlier age than people in the comparison group (males, 24.6 v. 30.7 years, females, 28.9 v. 33.1 years).<h4>Conclusions</h4>Cannabis-induced psychotic disorders are of great clinical and prognostic importance.