Bloomfield 1981.

Study characteristics
Methods	Randomised controlled trial.
Participants	Setting: single‐centre study at Cincinatti General Hospital ‐ time frame not given Inclusion criteria: women with moderate or severe postpartum uterine cramp pain within 48 hours of an uncomplicated birth Exclusion criteria: women given analgesics or other central nervous system drugs within previous 6 hours; women with a known allergy to aspirin or paracetamol (acetaminophen); women breastfeeding their babies
Interventions	Women were randomly allocated to 1 of 3 treatment groups, stratified by initial pain intensity, moderate or severe, and given a single oral dose (2 capsules) of 1 of the following: Aspirin 650 mg (N = 26) Paracetamol (acetaminophen) 650 mg (N = 22). Placebo (N = 26)
Outcomes	Adequate pain relief as assessed by the woman: women were interviewed by a trained nurse observer at baseline, ½ hour post‐treatment and hourly for 6 hours Pain intensity measured and scored on a 4‐point ordinal scale, no pain (0), mild (1), moderate (2) or severe (3). Pain intensity difference scores were calculated by subtracting baseline pain intensity scores from pain intensity scores at observed time points. Reported PID scores were used to calculate SPID scores and these were used to calculate 'adequate pain relief as assessed by the woman' (estimated over 6 hours) Women were asked to rate pain relief at the 3rd hour as greater than 50% or not Maternal adverse affects: women were asked about side effects with minimal use of leading questions and without use of a checklist at the final interview
Notes	Additional study arms: this study included an additional 2 arms of pirprofen 200 mg and 400 mg. This medication is no longer available, so these arms were not included. Study included a comparison of pirprofen. Since this medication not in current used it was not included Dates of study: not stated. Funding sources: study funded in part by grant from pharmaceutical company CIBA‐GEIGY Corporation Declarations of interest: no declaration of interests statement
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Quote: "Within each of the 2 pain strata there was a separate, balanced randomisation of patients". Women with moderate and women with severe pain intensity were evenly divided between the treatment groups Unclear exactly how random sequence was generated
Allocation concealment (selection bias)	Unclear risk	Not reported
Blinding of participants and personnel (performance bias) All outcomes	Low risk	Use of "identical coded capsules"
Blinding of outcome assessment (detection bias) All outcomes	Unclear risk	Not stated
Incomplete outcome data (attrition bias) All outcomes	Low risk	Data on all women randomised were reported. There were 26 women allocated to the aspirin and placebo groups and 22 women allocated to the paracetamol group. There are no reported withdrawals and the number of women included at baseline and reported for all outcomes is the same
Selective reporting (reporting bias)	Unclear risk	No protocol published or trial registration available
Other bias	Low risk	No other risk of bias identified