Methods	RCT, 2-arm parallel group design.
Participants	Setting: Washington, USA. 194 women in established labour. Analgesia was given at approximately 4-5 cm cervical dilatation
Interventions	Experimental: IV phenazocine 1 mg. Control: IV pethidine 50 mg. Both groups received promethazine 50 mg, and for both groups “birth was accomplished under pudendal nerve block anaesthesia with terminal self-administered trichloroethylene”
Outcomes	Pain relief (recorded by women on the first postpartum day); nausea and vomiting; adverse effects; progress in labour; Apgar scores at 1 and 5 mins
Notes
Risk of bias
Bias	Authors’ judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Not described.
Allocation concealment (selection bias)	Low risk	Drugs were prepared by pharmacy in identical coded vials and the code was not broken by the pharmacist until the study had been completed
Blinding (performance bias and detection bias) Women	Low risk	Drugs in identical vials.
Blinding (performance bias and detection bias) Clinical staff	Low risk	Pharmacy prepared identical coded drugs.
Blinding (performance bias and detection bias) Outcome assessor	Unclear risk	Unclear.
Incomplete outcome data (attrition bias) All outcomes	Low risk	Missing data for some outcomes (approximately 5% for maternal postpartum outcomes, and 10% for nurse recorded evaluations in labour)
Selective reporting (reporting bias)	Low risk	None apparent.
Other bias	Low risk	None apparent.