A Cochrane review included 4 cross-over studies with a total of 196 subjects. Due to significant methodological heterogeneity and differences in outcome measures it was not possible to summarise data in a meta-analysis. Only two of the studies reported a 50% or greater seizure reduction compared to placebo; 57.7% and 52.4%. Side effects were only described in two of the studies, reportedly present in 36% and 85% of patients.
Comment: The quality of evidence is downgraded by inconsistency (heterogeneity in methodology and outcomes) and by imprecise results (limited study size for each comparison).