Schachtel 1991a.

Methods	Single‐centre, randomised, double‐blind, placebo‐controlled, parallel‐group study Single oral dose after onset of relatively severe throat pain (> 66 mm on 100 mm VAS). Duration: 2 h, with assessments at baseline, 15, 30, 45, 60, 90, and 120 minutes post dose
Participants	Acute sore throat, with a score of ≥ 4 on 12‐point tonsillopharyngitis assessment and pain intensity > 66/100 on VAS Participants at least 18 years of age N = 210 (207 for efficacy) M 69, F 138 Mean age 30 years
Interventions	Aspirin 800 mg + caffeine 64 mg, n = 70 for efficacy Aspirin 800 mg, n = 68 for efficacy Placebo, n = 69 for efficacy No "cold medication", mood‐altering drugs, or alcohol within 8 h, or caffeine‐containing medication or beverages within 12 h of dosing
Outcomes	PI: 100 mm VAS PR: 6‐point categorical scale (from 'no relief' to 'complete relief') Withdrawals and dropouts
Notes	Oxford Quality Score: R2, DB1, W1. Total = 4/5
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Computer‐generated randomisation code
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