Herbal medicines: where is the evidence?
Growing evidence of effectiveness is counterbalanced by inadequate regulation
Sales of herbal medicines are booming. This is particularly true in the United States, where the market for herbal supplements is now approach. ing $4bn a year. The fastest growth has been recorded for St John's wort, a herbal antidepressant whose sales increased in one year by 2800%.1 Faced with such figures doctors are inclined to ask where the evidence is. Are there rigorous trials to show that herbal treatments work?
Single studies are unlikely to convince sceptics, but an increasing body of evidence is now emerging from systematic reviews and meta.analyses of randomised clinical trials. These suggest that some herbal medicines are efficacious. The increased demand for St John's wort, for instance, was triggered by press reports of a meta-analysis of 23 randomised trials of 1757 patients with mild or moderate depression. The authors concluded that extracts of hypericum were significantly more effective than placebo (odds ratio 2.67; 95%