Methods	RCT 2-arm parallel group design.
Participants	Stockholm Sweden, hospital setting. 20 healthy nulliparous women in active labour after spontaneous rupture of the membranes, cephalic presentation. No exclusion criteria specified
Interventions	Experimental: 0.05 mg/kg IV morphine up to 3 doses (max 0.15 mg/kg body weight) Control: 0.5 mg/kg IV pethidine up to 3 doses (max 1.5 mg/kg body weight) Both groups had continuous FHR monitoring.
Outcomes	Sedation rates; CS, nausea and vomiting.
Notes
Risk of bias
Bias	Authors’ judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	“assigned at random.”
Allocation concealment (selection bias)	Low risk	Coded ampoules provided by pharmacy.
Blinding (performance bias and detection bias) Women	Low risk	Described as double blind; pharmacy provided identical coded ampoules
Blinding (performance bias and detection bias) Clinical staff	Low risk	Described as double blind; pharmacy provided identical coded ampoules
Blinding (performance bias and detection bias) Outcome assessor	Unclear risk	Unclear.
Incomplete outcome data (attrition bias) All outcomes	Low risk	No apparent loss to follow-up.
Selective reporting (reporting bias)	Unclear risk	Unclear.
Other bias	Unclear risk	Small sample and no clear information that groups were comparable at baseline. Range of cervical dilations at recruitment between 4 and 9 cm