Methods	Multicentre, randomised, double-blind, placebo-controlled, parallel-group. Single oral dose Participants instructed to take medication only if attack of at least moderate intensity, and within 6 hours of onset of symptoms Assessments at 0, 0.5, 1, 1.5, 2, 3, 4, 5, 6 and 24 hours. If pain not controlled, participants asked to wait 2 hours before taking rescue medication
Participants	Aged 18-65 years, meeting IHS criteria for migraine. At least 12-month history of migraine, with one to six attacks per month Excluded participants Excluded participants usually so incapacitated as to require bed rest during attacks, and those who vomited more than 20% of time during attacks N = 374 (343 analysed for efficacy, 31 did not take medication) M = 62, F = 312 Mean age = 42 years
Interventions	Effervescent acetylsalicylic acid 2 × 500 mg, n = 169 Placebo, n = 174
Outcomes	Headache relief at 2 hours Pain-free after 2 hours Relief of migraine-associated symptoms: nausea, vomiting, photophobia, phonophobia (4-point scale) PI : 4-point scale PGE: 4-point scale Headache recurrence within 24 hours Use of rescue medication Adverse events
Notes	Oxford Quality Score: R1, DB1, W1. Total = 3.
Risk of bias
Item	Authors’ judgement	Description
Adequate sequence generation?	Unclear	Not described
Allocation concealment?	Unclear	Not described
Blinding? All outcomes	Unclear	Not described