Ali 2007.

Methods	Single‐centre, randomised, double‐blind, 3‐way cross‐over study, with a single oral dose administered at the onset of moderate or severe menstrual pain (and no later than 24 h after the onset of menstrual flow) Duration: 6 h, with assessments at baseline, 0.5, 1, 2, 3, 4, 5, and 6 h post dose
Participants	Primary dysmenorrhoea ‐ graded 2 or 3 on the Andersch and Milsom scoring system over 3 of the 4 previous menstrual cycles and requiring medication with OTC analgesics. Menstrual cycle duration between 21 and 35 days, and adequate past response to OTC analgesics for treatment of dysmenorrhoea Participants aged 18 years or older N = 320 (310 for efficacy) All F Mean age 21 years
Interventions	Paracetamol 1000 mg + caffeine 130 mg, n = 320 (310 for efficacy) Paracetamol 1000 mg, n = 320 (310 for efficacy) Caffeine 130 mg, n = 160 (155 for efficacy) Placebo, n = 160 (155 for efficacy) No alcohol or caffeine within the 6 h before and after dosing. No concomitant use of analgesics, psychoactive drugs, antispasmodics, natural treatments, or devices such as hot water bottles and heated pads within 6 h before or after dosing
Outcomes	PI: standard 4‐point scale PR: standard 5‐point scale Withdrawals and dropouts Serious adverse events
Notes	Oxford Quality Score: R2, DB2, W1. Total = 5/5
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Computer‐generated randomisation schedule
Allocation concealment (selection bias)	Unclear risk	Method not described
Blinding of participants and personnel (performance bias) All outcomes	Low risk	All treatments were supplied unmarked and blister packed. "caffeine and placebo tablets custom manufactured ... and matched the size and shape of the paracetamol‐containing caplets"
Size	Low risk	> 200 participants in relevant treatment arms