Ward 1991.

Methods	Single‐centre, randomised, double‐blind, placebo‐controlled, 6‐period cross‐over study Single oral dose administered to treat a headache rated ≥ 2 on the McGill Pain Questionnaire Only 1 test dose could be taken on any given day Duration: 2 h, with assessments at baseline, 0.5, 1, 2 h
Participants	Headache: participants with no history of migraines and with headaches that had no migrainous features ≥ 6 headaches per month during the past 3 months with pain severity averaging ≥ 2 on a 5‐point scale Participants were 18 to 60 years of age N = 60 completed the study (53 for efficacy) M 17, F 36 Mean age 37 years
Interventions	Paracetamol 648 mg + caffeine 65 mg, n = 53 Paracetamol 648 mg + caffeine 130 mg, n = 53 Paracetamol 648 mg, n = 53 Caffeine 65 mg, n = 53 Caffeine 130 mg, n = 53 Placebo, n = 53 No caffeine or other analgesics during the 2‐h study period. Participants documented any caffeine consumed in the 24 h before dosing
Outcomes	PI: 100 mm VAS ('no pain' at left end, 'pain as bad as it could be' at right end' and 'mild, moderate, severe' in sequence below the line)
Notes	Oxford Quality Score: R1, DB1, W0. Total = 2/5
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)	Unclear risk	Method not described
Blinding of participants and personnel (performance bias) All outcomes	Unclear risk	Method not described
Size	High risk	All relevant treatment groups borderline at 53 participants each