Zissis 2007.

Methods	Six‐centre, randomised, double‐blind: venlafaxine XR vs placebo
Participants	Country: Greece N = 60. Sex: 11 male 49 female Mean age: 40.8 (SD 14.5) Diagnosis: all subtypes of tension‐type headache according to International Headache Society Criteria (IHS 2004) Exclusion criteria: patients < 18 years old, patients with headache for < 5 days/month, patients with < 21 in the Migraine Disability Assessment (MIDAS) questionnaire. No current depression or anxiety disorders
Interventions	N = 34 venlafaxine XR to a maximum of 150 mg/day N = 26 Placebo Active treatment: 12 weeks
Outcomes	1. Number of days with headache 2. Number of hours with headache 3. Total headache intensity index (duration x severity) 4. Clinical global impression improvement
Notes	40 completers, 25 venlafaxine XR, 15 placebo Adequate sample size calculation, intention‐to‐treat analysis using the last‐observation‐carried‐forward method
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Random numbers table
Allocation concealment (selection bias)	Low risk	Sealed envelopes
Blinding (performance bias and detection bias) All outcomes	Low risk	Venlafaxine XR and placebo were supplied as identically appearing capsules; the drug was dispensed by the hospital pharmacies
Incomplete outcome data (attrition bias) All outcomes	High risk	High dropout rate (20/60 = 33%), unbalanced (venlafaxine XR 9/34 = 26.5%, placebo 11/26 = 42.3%)
Selective reporting (reporting bias)	Unclear risk	No information
Other bias	High risk	Financial support not reported but the randomisation and the blinding were done by the drug company