Clinical trials and systematic reviews of herbal medicine

The popularity of herbal medicines begs the question whether a given herbal remedy is safe and efficacious in treating a given condition. The latter question is best answered on the basis of randomised (preferably placebo-controlled, double-blind) clinical trials. Several hundred clinical trials of variable methodological rigour have been published. The emerging evidence is often contradictory. In this situation the best evidence is provided by a systematic review or meta-analysis, i.e. an evaluation of the totality of all the available studies on a specific topic. This approach is aimed at minimising both random and selection biases. Today well over 100 systematic reviews relating to a wide range of herbal medicines have been published. Examples of some of these systematic reviews will be discussed. They leave little doubt that some herbal medicines are efficacious in treating some clinical conditions.

To date the evidence relating to safety is largely anecdotal, i.e. based on case reports. The least biased and most informative tool for summarising it is again the systematic review. Several systematic reviews of safety data will be provided. Their results vary but, by and large, suggest that adverse effects are rare.

In conclusion, more systematic research is required to evaluate the balance between risk and benefit for commonly used herbal medicines.