Ref (type)	Population	Outcome, Interventions	Results and statistical analysis	Effect size	Favours
Adverse effects
[18] RCT	70 people with chronic daily headache (41 with CTTH and 29 with chronic migraine; diagnostic criteria used were unclear)	Adverse effects 3 months 3/40 (8%) with sodium valproate 1/30 (3%) with placebo	Significance not assessed