Study designs of evaluations included in the review
All study designs were eligible for inclusion. The included studies were case series and case reports.
Specific interventions included in the review
Interventions eligible for inclusion were those that used niacin as the sole therapeutic agent to treat headache. The included interventions were niacin administered orally (regular or sustained-release), intravenously and by intramuscular injection. Some interventions involved the daily administration of niacin over a period of weeks or months. Exact details of the interventions, including dosage, were tabulated.
Participants included in the review
Studies of patients with migraine or any other type of headache were eligible for inclusion. The participants had chronic or acute headaches, including migraine, tension, idiopathic and spinal tap headaches.
Outcomes assessed in the review
No inclusion criteria for the outcome measures were specified. The included studies reported headache relief and reduction in the numbers of headaches occurring; the outcomes were generally evaluated by self-report. Adverse events were also discussed.
How were decisions on the relevance of primary studies made?
The authors did not state how the studies were selected for the review, or how many reviewers performed the selection.