Risk of transition to schizophrenia following first admission with substance-induced psychotic disorder: a population-based longitudinal cohort study

BACKGROUND The potential for drugs of abuse to induce acute psychotic symptoms is well recognised. However, the likelihood of transition from initial substance-induced psychotic disorder (SIPD) to chronic psychosis is much less well understood. This study investigated the rate of SIPD transition to schizophrenia (F20), the time to conversion, and other possible related factors.
METHODS Using data from the Scottish Morbidity Record, we examined all patients (n=3486) since their first admission to psychiatric hospital with a diagnosis of SIPD (ICD-10 codes F10-F19, with third digit five) from January 1997 to July 2012. Patients were followed until first episode of schizophrenia (ICD-10 code F20, with any third digit) or July 2012. Any change in diagnosis was noted in the follow-up period, which ranged from one day to 15.5 years across the groups.
RESULTS The 15.5 year cumulative hazard rate was 17.3% (SE=0.007) for a diagnosis of schizophrenia. Cannabis, stimulant, opiate and multiple drug induced psychotic disorder were all associated with similar hazard rates. The mean time to transition to a diagnosis of schizophrenia was around 13 years, although over 50% did so within two years and over 80% of cases presented within five years of SIPD diagnosis. Risk factors included male gender, younger age, and longer first admission.
CONCLUSIONS SIPD episodes requiring hospital admission for more than two weeks are more likely to be associated with later diagnosis of schizophrenia. Follow-up periods of more than two years are needed to detect the majority of those individuals who will ultimately develop schizophrenia.