Methods	RCT, 2-arm parallel groups.
Participants	Hospital setting. 199 women: in labour, at term gestation, following normal pregnancy No inclusion or exclusion criteria reported.
Interventions	Experimental: IM pentazocine 20-40 mg (N = 91). Control: IM pethidine 50-100mg(N= 89).
Outcomes	Primary: analgesic and sedative effects. Pain assessed at time of birth or when second injection administered, as very good, good, moderate or none Secondary: maternal and neonatal side effects.
Notes	If additional analgesia required opioid repeated once after 3 or > hrs of first injection. Actual dose received by women not reported
Risk of bias
Bias	Authors’ judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Not reported.
Allocation concealment (selection bias)	Unclear risk	Ampoules numbered and in random order.
Blinding (performance bias and detection bias) Women	Unclear risk	Reported as double blind, but no description of how achieved. Identical volume but appearance not described
Blinding (performance bias and detection bias) Clinical staff	Unclear risk	Reported as double blind, but no description of how achieved. Identical volume but appearance not described
Blinding (performance bias and detection bias) Outcome assessor	Unclear risk	Not reported.
Incomplete outcome data (attrition bias) All outcomes	Low risk	All participants analysed, but missing data for some outcomes
Selective reporting (reporting bias)	Unclear risk	Unclear.
Other bias	Low risk	Balanced at baseline for age, parity, blood pressure, pulse, frequency contractions, FHR, augmented labour, intensity of labour, membranes intact or ruptured