Ref (type)	Population	Outcome, Interventions	Results and statistical analysis	Effect size	Favours
Headache relief
RCT Crossover design	19 men with cluster headache In review	Complete or substantial relief in 80% or more of attacks 9/16 (56%) with oxygen (100% at 6 L/minute for up to 15 minutes) 1/14 (7%) with air	RR 7.88 95% CI 1.13 to 54.66 RR calculated by review See further information on studies for methodological issues	Large effect size	oxygen
RCT Crossover design	19 men with cluster headache In review	Average pain relief score 1.93 with oxygen (100% at 6 L/minute for up to 15 minutes) 0.77 with air	P <0.01 See further information on studies for methodological issues	Effect size not calculated	oxygen