Gatoulis 2012.

Methods	R, DB, AC, and PC, parallel groups 1 episode treated with a single dose of study medication when pain was ≥ mod intensity Participant diary
Participants	Episodic TTH (IHS), 2‐10 episodes/month. Able to distinguish from migraine Excl: known allergy to study interventions, previous non‐response to active interventions, significant medical history, recent head injury n = 559 (safety population), 487 (efficacy) M 183, F 304 Mean age 37 years (range 18‐66 years) Baseline PI: 76% mod, 24% severe
Interventions	Paracetamol 300 mg + codeine 30 mg, n = 233 Aspirin 1000 mg, n = 223 Placebo, n = 103 Rescue medication (usual treatment) allowed. No timing given
Outcomes	PI: 4‐point scale (0.5, 1, 2, 3, 4 5, 6 h) PR: 5‐point scale
Notes	Oxford Quality Score: R1, DB2, W1
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	"Individuals were randomly assigned". Method of sequence generation not reported
Allocation concealment (selection bias)	Unclear risk	Not reported
Blinding of participants and personnel (performance bias) All outcomes	Low risk	Double dummy method
Blinding of outcome assessment (detection bias) All outcomes	Low risk	Double dummy method
Incomplete outcome data (attrition bias) All outcomes	Unclear risk	7‐14% attrition. Imputation method not reported
Size	Unclear risk	50‐200 participants in each treatment arm (103‐233)