Wen 2015.

Methods	Allocation: randomised (no detailed information). Blindness: single blind. Duration: 12 weeks. Design: multicentre, parallel. Setting: inpatients and outpatients. Country: China.
Participants	Diagnosis: schizophrenia (DSM‐IV). N = 63. Age: mean age 37.1 years. Sex: 43% female. History: treatment with clozapine for > 12 weeks at a dose > 400 mg with no improvement observed, PANSS score ≥ 80 and CGI‐S ≥ 4.
Interventions	1. Clozapine plus ziprasidone: clozapine mean baseline dose = 479 mg/day (SD 56.5), ziprasidone was titrated from 80 mg/day up to 120 mg/day to 160 mg/day, 1 week after ziprasidone was added, the dose of clozapine was reduced accordingly. N = 31. 2. Clozapine plus quetiapine: clozapine mean baseline dose = 481.3 mg/day (SD 51.7), quetiapine was titrated from 200 mg/day up to 400 mg/day to 750 mg/day, 1 week after quetiapine was added, the dose of clozapine was reduced accordingly. N = 32.
Outcomes	Clinically significant response: > 50% reduction PANSS. Clinical response: global state (CGI‐S), mental state (PANSS total, PANSS positive, PANSS negative). Adverse effects: rate, agitation, constipation, drowsiness, dry mouth, extrapyramidal adverse effects, headache, insomnia, orthostatic hypotension, tachycardia, vertigo. Leaving the study early.
Notes	Chinese language.
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Randomisation was performed, no detailed information provided.
Allocation concealment (selection bias)	Unclear risk	No data.
Blinding of participants and personnel (performance bias) All outcomes	Unclear risk	Described as single blind.
Blinding of outcome assessment (detection bias) All outcomes	Low risk	The participants were evaluated by 3 doctors who did not have knowledge about the treatment allocation.
Incomplete outcome data (attrition bias) All outcomes	Low risk	3 participants who dropped out were excluded from the analyses of global and mental state outcomes, but included in the analyses of adverse events. Since the attrition rate was < 5%, and reasons were balanced between groups, the study was rated as low risk.
Selective reporting (reporting bias)	Unclear risk	No protocol available.
Other bias	Unclear risk	We could not rule out the potential for other bias.

General

n: number of participants

SD: standard deviation

Diagnostic tools

CCDM‐2‐R: Chinese Classification of Mental disorders

DSM‐IV: Diagnostic and Statistical Manual of mental disorders, fourth edition

Global effects scales

CGI: Clinical Global Impression

CGI‐S: Clinical Global Impression ‐ Severity

GAF: Global assessment of functioning

Mental state scales

BPRS: Brief Psychiatric Rating Scale

HAMD: Hamilton Depression Scale

PANSS: Positive and Negative Syndrome Scale

SANS: Scale for the Assessment of Negative Symptoms

SAPS: Scale for the Assessment of Positive Symptoms

Adverse effect scales

EPS: Extrapyramidal Symptoms Scale

HAS: Hillside Akathisia Scale

LUNSERS: Liverpool University Neuroleptic Side Effect Rating Scale

SAS: Simpson‐Angus Extrapyramidal Symptoms Rating Scale

TESS: Treatment Emergent Symptom Scale

UKU: Udvalg for Kliniske Undersgelser Side Effect Rating Scale