What types of evidence exists for the safety and effectiveness of herbs and how strong is that evidence?
Only a few herbs have been studied in randomized, double-blind, clinical trials, the type of study that provides the strongest evidence for the effectiveness of a medical treatment. Without the kind of evidence that comes from a clinical trial it is very difficult, if not impossible, to judge the safety and efficacy of herbal medicines. In the absence of evidence from a clinical trial, the potential effectiveness of an herbal medicine can only be judged based on traditional use or research that can only assess one narrow aspect of an herbal medicine. For example, there are cellular and animal studies that can give an estimate of the biological activity of herbal medicines and their potential for various treatments, but these studies poorly reflect their safety and efficacy in the human body. Nonetheless, a single clinical trial can give misleading results. Consistent results from several well designed and conducted clinical trials are needed to be sure a medicine is safe and effective.
