TABLE 1.

Frequency of antipsychotic combinations

Study/country	N and populationa	Antipsychotic polypharmacy (prescribing ≥2 antipsychotics at the same time) as defined in each study	Prevalence of antipsychotic polypharmacy	Duration of follow-up
Leslie and Rosenheck (14), United States	N=34,925 VA outpatients with schizophrenia taking oral antipsychotics	Prescribed antipsychotics for one week June–Sept. 1999	6.8% (2,383) received prescriptions for combination antipsychotics	June–Sept 1999
Jaffe and Levine (15), United States	N=7,130 inpatients in NY state psychiatric hospital system receiving antipsychotics	Polypharmacy episode ≥28 days	37.3% (2,791) patients were on combination antipsychotics, of whom 0.12% (342) received three or more antipsychotics; mean duration of polypharmacy=97 days	1999
Ganguly et al. (3), United States	N=31,435 Medicaid recipients in California and Georgia, ≥16 years old	Study inclusion criteria: ≥14 days of antipsychotics combination; polypharmacy episode ≥31 days; long-term polypharmacy ≥ 60 days	Overall polypharmacy 40% (N=12,549); long-term polypharmacy 23% (N=7,222); mean duration of long-term polypharmacy=236 days	1998–2000
Humberstone et al (16), New Zealand	N=3,178 outpatients with schizophrenia and bipolar disorder on antipsychotics	Cross-sectional prescribing practice, March 2000	Polypharmacy among 16.4% (N=521) of the total sample; 254 on oral antipsychotic only; 267 on oral + long-acting injectable antipsychotic	March 2000
Kreyenbuhl et al. (4), United States	N=61,257 patients in VA National Psychosis Registry	≥30 days polypharmacy	20.0% (12,234) for ≥30 days	2000
		≥ 60 days polypharmacy	13.1% (N=8,050) for ≥60 days
		≥ 90 days: long-term polypharmacy	9.5% (N=5,826) for ≥90 days
Tiihonen et al. (13), Finland	N=8,719 persons with first-episode schizophrenia and N=62,250 inpatients with schizophrenia from Hospital Discharge Register, National Prescription Register, and National Death Register in Finland	>90 days polypharmacy	41.6% (N=3,627) of patients with first-episode schizophrenia were on antipsychotic polypharmacy for >90 days; 57.5% of all inpatients with schizophrenia (N=62,250), were on polypharmacy when followed for the same duration of time	1996–2015 (median follow-up=14 years)

^aVA, Department of Veterans Affairs.