Methods	RCT, 2-arm parallel group design.
Participants	Setting not clear (hospital in USA). 100 women in good health in active labour, with no addiction to or tolerance to drugs and complaining of moderate to severe pain. Women who “planned to nurse” were excluded
Interventions	Experimental: (50 women) IV butorphanol 1-2 mg (44 women had an initial dose of 1 mg and 6 an initial dose of 2 mg, after one hr or more a 2nd dose was given if requested) Control: (50 women) IV pethidine 40-80 mg (45 women had an initial dose of 40 mg and 5 an initial dose of 80 mg, a 2nd dose was given after 1hr or more if requested)
Outcomes	Pain (5-point scale 0 - no pain, 4 - very severe pain); pain relief (5-point scale 0 - none, 4 - complete relief); FHR; Apgar scores at 1 and 5 minutes
Notes
Risk of bias
Bias	Authors’ judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Not described.
Allocation concealment (selection bias)	Unclear risk	Not described.
Blinding (performance bias and detection bias) Women	Unclear risk	Described as double blind study but no details provided.
Blinding (performance bias and detection bias) Clinical staff	Unclear risk	Unclear.
Blinding (performance bias and detection bias) Outcome assessor	Unclear risk	Unclear.
Incomplete outcome data (attrition bias) All outcomes	Unclear risk	Outcome data were available for all women randomised.
Selective reporting (reporting bias)	Unclear risk	Unclear.
Other bias	Unclear risk	No baseline imbalance was apparent although 8 women in the butorphanol group were induced compared with 1 woman in the pethidine group