Brunstein 2005.

Methods	Allocation: randomised, no further details. Blindness: double‐blind. Duration: six weeks. Setting: Brazil (mixed inpatients and outpatients) Design: cross‐over (but able to use data from first arm).
Participants	Diagnosis: schizophrenia (DSM‐IV) and "moderately refractory". N = 35 (N = 23 for completer analysis). Sex: 9F, 14M (12 unclear because of completer analysis). Age: average 35.3 years (allopurinol), 42.3 years (placebo).
Interventions	1. Allopurinol: 600mg/day. N = 18. 2. Placebo. N = 17. Stable neuroleptic medication: dose average (CPE) 550 (allopurinol), 545(placebo).
Outcomes	Global state: response (20% improvement in the PANSS). Leaving the study early. Mental state: PANSS change score. Adverse events: various and serious events.
Notes	Able to use LOCF analysis for total PANSS scores and response.
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Randomised, no further details.
Allocation concealment (selection bias)	Unclear risk	No further details.
Blinding of participants and personnel (performance bias) All outcomes	Low risk	Double‐blind.
Blinding of outcome assessment (detection bias) All outcomes	Unclear risk	No further details.
Incomplete outcome data (attrition bias) All outcomes	Low risk	LOCF analysis reported.
Selective reporting (reporting bias)	Low risk	Main outcomes reported.
Other bias	Low risk	None obvious.