Diamond 2000.

Methods	Multicentre, randomised, double‐blind, placebo‐controlled, parallel‐group study, with a single oral dose administered (baseline pain intensity not reported) Duration: 6 h, with assessments at baseline, 15, 30, 45, 60, 90, and 120 minutes, then hourly through to 6 h post dose
Participants	Acute tension‐type headache ‐ in accordance with IHS criteria, with 3 to 15 tension‐type headaches every month for ≥ 1 year, and ≥ 75% of headaches responsive to non‐prescription‐strength analgesics Participants with occasional migraine headaches (< 2 per month) were not excluded provided they could differentiate the two types of headache No alcohol, caffeine‐containing foods/beverages, or any other analgesic within 4 h before dosing Participants at least 18 years of age N = 331 (301 for efficacy) M 57, F 244 Mean age 37 years
Interventions	Ibuprofen 400 mg + caffeine 200 mg, n = 97 for efficacy Ibuprofen 400 mg, n = 99 for efficacy Caffeine 200 mg, n = 57 for efficacy Placebo, n = 48 for efficacy
Outcomes	PI: standard 4‐point scale PR: standard 5‐point scale PGE: standard 5‐point scale Withdrawals and dropouts
Notes	Oxford Quality Score: R1, DB1, W1. Total = 3/5
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	Unclear risk	50 to 200 participants in relevant treatment arms