A Cochrane review [Abstract] 1 included 75 randomised trials, with a total of 7 957 subjects, but the methodological quality was high in only 3 double-blind, placebo-controlled trials. Seventy-one different herbal medicines were tested in the included trials, in which herbal medicines were compared with placebo or conventional pharmacologic therapy. Herbal medicines were also combined with conventional therapy and compared to conventional therapy alone.
Compared with placebo, a Standard Chinese herbal formula, individualised Chinese herbal medicine, STW 5 and STW 5-II, Tibetan herbal medicine Padma Lax, traditional Chinese formula Tongxie Yaofang, and Ayurvedic preparation showed significant improvement of global symptoms. No serious adverse events from the herbal medicines were reported.
Comment: The quality of evidence is downgraded by study quality (e.g. inadequate or unclear allocation concealment and blinding), by imprecise results (limited study size for each comparison) and by inconsistency (heterogeneity in diagnostic criteria, interventions and outcomes). Most of the trials comparing herbal medicines with conventional therapies do not offer convincing evidence to support their use due to methodological flaws, heterogeneity in the definition of diagnostic criteria, and lack of placebo control and blinded measurement of subjective outcomes.
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