Methods	Participants recruited from 5 international headache centres; out-patient based R, DB, two-period cross-over study; 24 h washout Two headache episodes treated with each of two treatments
Participants	Established IHS diagnosis of cluster headache N = 118 randomised, 85 in efficacy analysis Mean age 43 ± 11 years 82% men Headache type: 75% episodic
Interventions	Sumatriptan 20 mg, nasal spray, n = 77 Placebo, n = 77 Patients instructed to take medication when headache reached at least moderate intensity Escape medication permitted after 30 min
Outcomes	Primary: Pain relief to mild or none at 30 min on a five-point scale Secondary: Pain-free at 30 min; relief of associated symptoms; time to initial relief; use of rescue medication; adverse events; withdrawals
Notes	Oxford Quality Score: 4 (R1, DB2, W1)
Risk of bias
Item	Authors’ judgement	Description
Adequate sequence generation?	Unclear	Not described
Allocation concealment?	Unclear	Not described
Blinding? All outcomes	Yes	Matching placebo

Abbreviations: DB - double blind; N - number of participants in study; n - number of participants in treatment group; R - randomised; W - withdrawals