Methods	RCT 2-arm parallel group design.
Participants	Setting: UK hospital. 94 women. > 35 weeks’ gestation, age ≥ 18 years, excluded if diabetic, history of renal or hepatic impairment or taking monoamine oxidase inhibitors, in active labour and requiring analgesia Parity: ≤ 3.
Interventions	Experimental: IM pentazocine 60 ≤ mg (N = 46). Control: IM pethidine 15 ≤ 0 mg (N = 48). Up to 3 injections > 3 hours apart at maternal request.
Outcomes	Maternal outcomes: satisfied with analgesia, nausea, vomiting, sleepiness, use of additional analgesia (study drug), method of birth. Neonatal outcomes: Apgar at 1 and 5 min
Notes	Data for some outcomes available after first dose.
Risk of bias
Bias	Authors’ judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Not reported.
Allocation concealment (selection bias)	Unclear risk	Not reported.
Blinding (performance bias and detection bias) Women	Unclear risk	States double blind but how achieved not reported.
Blinding (performance bias and detection bias) Clinical staff	Unclear risk	States double blind but how achieved not reported.
Blinding (performance bias and detection bias) Outcome assessor	Unclear risk	States double blind but how achieved not reported.
Incomplete outcome data (attrition bias) All outcomes	High risk	Exclusions from most analyses.
Selective reporting (reporting bias)	Unclear risk	Unclear.
Other bias	Low risk	Balanced at baseline for age, parity, induced labour onset.