Laska 1983 Study 1.

Methods	Single‐centre, randomised, double‐blind, placebo‐controlled, parallel‐group study Single oral dose administered after onset of moderate or severe pain Almost identical protocols for Studies 1, 2, 3 Duration: 4 h, with assessments baseline, 0.5, 1, 2, 3, and 4 h post‐dose
Participants	Postpartum pain: postepisiotomy, postsurgical, or uterine cramping N = 480 (373 in final analysed sample) No further participant characteristics reported
Interventions	Paracetamol 500 mg + caffeine 65 mg, n = 56 Paracetamol 500 mg, n = 54 Paracetamol 1000 mg + caffeine 130 mg, n = 57 Paracetamol 1000 mg, n = 50 Paracetamol 1500 mg + caffeine 195 mg, n = 56 Paracetamol 1500 mg, n = 60 Placebo, n = 40 Numbers of participants are those in final analysed sample Medications that might alter the response to the study analgesic during the study or in the 4 h preceding were prohibited. Participants who had taken caffeine during the 3 h before and after dosing were excluded
Outcomes	PI: standard 4‐point scale PR: standard 5‐point scale Withdrawals and dropouts
Notes	Oxford Quality Score: R1, DB2, W1. Total = 4/5
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Method used to generate random sequence not described
Allocation concealment (selection bias)	Low risk	"sequentially assigned from individual packages prepared in random order"
Blinding of participants and personnel (performance bias) All outcomes	Low risk	Test medication prepared to look exactly like the standard paracetamol 500 mg tablet. Equal numbers of tablets given to each group in any study
Size	Unclear risk	50 to 200 participants in relevant treatment arms