The effectiveness of antipsychotic polypharmacy in schizophrenia relapse prevention is controversial, and use of multiple agents is generally believed to impair physical well-being.

To study the association of specific antipsychotic combinations with psychiatric rehospitalization.

In this nationwide cohort study, the risk of psychiatric rehospitalization was used as a marker for relapse among 62 250 patients with schizophrenia during the use of 29 different antipsychotic monotherapy and polypharmacy types between January 1, 1996, and December 31, 2015, in a comprehensive, nationwide cohort in Finland. We conducted analysis of the data from April 24 to June 15, 2018. Rehospitalization risks were investigated by using within-individual analyses to minimize selection bias.

Hazard ratio (HR) for psychiatric rehospitalization during use of polypharmacy vs during monotherapy within the same individual.

In the total cohort, including 62 250 patients, 31 257 individuals (50.2%) were men, and the median age was 45.6 (interquartile range, 34.6-57.9) years. The clozapine plus aripiprazole combination was associated with the lowest risk of psychiatric rehospitalization in the total cohort, being superior to clozapine, the monotherapy associated with the best outcomes, with a difference of 14% (HR, 0.86; 95% CI, 0.79-0.94) in the analysis including all polypharmacy periods, and 18% in the conservatively defined polypharmacy analysis excluding periods shorter than 90 days (HR, 0.82; 95% CI, 0.75-0.89; P < .001). Among patients with their first episode of schizophrenia, these differences between clozapine plus aripiprazole vs clozapine monotherapy were greater (difference, 22%; HR, 0.78; 95% CI, 0.63-0.96 in the analysis including all polypharmacy periods, and difference, 23%; HR, 0.77; 95% CI, 0.63-0.95 in the conservatively defined polypharmacy analysis). At the aggregate level, any antipsychotic polypharmacy was associated with a 7% to 13% lower risk of psychiatric rehospitalization compared with any monotherapy (ranging from HR, 0.87; 95% CI, 0.85-0.88, to HR, 0.93; 95% CI, 0.91-0.95; P < .001). Clozapine was the only monotherapy among the 10 best treatments. Results on all-cause and somatic hospitalization, mortality, and other sensitivity analyses were in line with the primary outcomes.

Combining aripiprazole with clozapine was associated with the lowest risk of rehospitalization, indicating that certain types of polypharmacy may be feasible in the treatment of schizophrenia. Because add-on treatments are started when monotherapy is no longer sufficient to control for worsening of symptoms, it is likely that the effect sizes for polypharmacy are underestimates. Although the results do not indicate that all types of polypharmacy are beneficial, the current treatment guidelines should modify their categorical recommendations discouraging all antipsychotic polypharmacy in the maintenance treatment of schizophrenia.