Skovlund 1991b.

Study characteristics
Methods	Randomised controlled trial with a sequential trial design
Participants	Location: country Norway but site not clearly identified (maybe Akershus Central hospital, Oslo, Norway) and time of study not stated Included: postpartum women with uterine cramps and possible concomitant episiotomy pain after vaginal birth requesting analgesia. Data from 56 participants were included in the sequential test but 60 participants were included in the estimation effect on uterine cramping Excluded: Women allergic to paracetamol or naproxen or with peptic disease
Interventions	Women were randomly allocated to 1 of 2 groups. Paracetamol 1000 mg (2 tablets paracetamol 500 mg, 1 tablet placebo) (N = 36) Naproxen 500 mg (1 tablet naproxen 500 mg and 2 tablets placebo) (N = 28) The medications were Identical in appearance
Outcomes	Pain however assessed by the authors: women were asked to rate their pain on a VAS measuring 100 mm at trial entry and again at 2 and 4 hours post medication. Uterine pain intensity (mm on VAS) and uterine pain intensity difference (mm on VAS) at 2 and 4 hours after medication Maternal adverse events: women were asked if they experienced any adverse events; none were suggested to them. Adverse events were recorded as women reported them
Notes	Sequential design Dates of study: not stated Funding sources: 1st author supported by a grant from the Norwegian Research Council for Science and the Humanities Declarations of interest: declared as none
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Study simply described as randomised
Allocation concealment (selection bias)	Unclear risk	No information related to allocation concealment
Blinding of participants and personnel (performance bias) All outcomes	Unclear risk	States "double dummy technique used to make the study double blind" but unclear who was blinded
Blinding of outcome assessment (detection bias) All outcomes	Unclear risk	Not stated
Incomplete outcome data (attrition bias) All outcomes	Low risk	There were 36 women allocated to the paracetamol group and 28 women to the naproxen group. 3 women excluded as misunderstood administration of medication (2 in paracetamol group, 1 in naproxen group). 1 excluded from paracetamol group as experienced only episiotomy pain Results included for 4 women in paracetamol group who were under study when the stopping boundaries for this sequential design trial were reached.
Selective reporting (reporting bias)	Unclear risk	No published protocol or trial registration available
Other bias	Low risk	Similar numbers of women in both groups (18 of the 36 paracetamol participants and 9 of the 28 naproxen group) had pain medication before enrolled into the trial, inclusion criteria stated they had pain and were requesting analgesia