Herbal medicines are preparations containing exclusively plant material. Their efficacy can be tested in clinical trials much like synthetic drugs but numerous methodological and logistical problems exist. For several herbal medicines, efficacy has been established; for many others, this is not the case mostly because the research has not been done. Many consumers believe that herbal medicines are natural and therefore safe. This is a dangerous simplification. Some herbal medicines are associated with toxicity others interact with synthetic drugs. The often under-regulated quality of herbal medicines amounts to another safety issue. Contamination or adulteration of herbal medicines are possible and can cause harm. In order to conduct a risk-benefit analysis of a specific herbal medicine for a specific indication, we require definitive efficacy and safety data. This is currently the case for only very few such preparations. It follows that, in order to advise consumers responsibly, the gaps in our present knowledge require filling.