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Substance use disorders associated with conversion to schizophrenia

Cannabis, amphetamine and opioid use disorders were all associated with conversion from schizotypal disorder to schizophrenia, study findings published in JAMA Psychiatry revealed.

“Previous results suggest that substance use, in particular cannabis, may be associated with conversion to schizophrenia in individuals with schizotypal disorder. The potential role of other substances has not, to our knowledge, been investigated previously,” Carsten Hjorthøj, PhD, MSc, of Copenhagen-University Hospital, Denmark, and colleagues wrote. “Further investigation of this proposed association may provide physicians and psychiatrists with better tools for preventing or detecting onset of schizophrenia in individuals with schizotypal disorder regardless of whether such an association is causal or simply an indicator of risk.”

In this prospective cohort study, researchers assessed whether substance use disorders — particularly cannabis use disorder — among people with schizotypal disorder were associated with conversion to schizophrenia using data from a population-based sample of individuals born in Denmark from Jan. 1, 1981 to Aug. 10, 2014. The investigators examined time-varying data on substance use disorders and receipt of antipsychotics, adjusting for parental psychiatric history, sex, birth year and calendar year.

Overall, 2,539 people with incident schizotypal disorder were included in the study. Results from the fully adjusted analyses revealed that any substance use disorder (HR =1.34; 95% CI, 1.11-1.63), opioid use disorder (HR = 2.74; 95% CI, 1.38-5.45), cannabis use disorder (HR = 1.3; 95% CI, 1.01-1.68), amphetamine use disorder (HR = 1.9; 95% CI, 1.14-3.17) and antipsychotic use (HR = 1.42; 95% CI, 1.18-1.7) were all linked with conversion to schizophrenia. Concurrent use of antipsychotics, functional level before schizotypal disorder diagnosis or parental history of psychiatric illness did not explain these associations.

After 2 years, 16.3% (95% CI, 14.8-17.8) of participants experienced conversion to schizophrenia. After 20 years, the conversion rate from schizotypal disorder to schizophrenia was 33.1% (95% CI, 29.3-37.3) overall among those with any substance use disorder; 58.2% (95% CI, 44.8-72.2) among those with cannabis use disorders; and 47% (95% CI, 35.3-60.2) among those with alcohol use disorder. Among participants without a substance disorder, the 20-year conversion rate was 30.6% (95% CI, 27.7-34.5).

“An increased focus on how to prevent conversion from schizotypal disorder to schizophrenia is required,” Hjorthøj and colleagues wrote. “Preventing or treating substance use disorders, especially cannabis and amphetamine use disorders, may have some efficacy in reducing the additional risk attributable to substance use disorders, but probably not below the already high baseline conversion rate.” – by Savannah Demko

Disclosures: The authors report no relevant financial disclosures.