Epidemiologic challenges in the study of the efficacy and safety of medicinal herbs

Although clinical trials are needed to prove the efficacy of medicinal herbs and pharmacological studies are essential to the long-term goal of identifying the active ingredients in plants, these will not be forthcoming rapidly enough to meet the acute public health needs for knowledge on efficacy and safety since these substances are currently being widely consumed at various dosages. Resulting from the ongoing 'natural experiment' well-conducted observational epidemiology can bridge the gap and determine whether, as consumed its use is of benefit or detrimental, for whom and when in the course of disease prevention or minimization of disease severity. The classic study designs (cohort and case-control) and the more recent development of case-only studies can be put to service for these purposes. The challenges are in dose assessment, understanding mechanisms of effect, determining the relevant time period of exposure for a given disease or symptom, controlling for confounding factors such as disease status, and the special challenges presented by irregular use of medicinal herbs and concurrent use of multiple products and multiple sources.