Herbal products are considered dietary supplements from a regulatory point of view. If we apply the basic principles of pharmacology to herbal medicines they can be classified into three groups: 1) products whose efficacy has been demonstrated: their active principles are known and the therapeutic doses are established; 2) herbal products whose efficacy is probable, but not clearly demonstrated: they contain pharmacologically active substances that are used to standardize the products. Their therapeutic dose is difficult to establish; 3) products with uncertain efficacy but with a long lasting traditional use: they can be useful for treating minor disorders, but should be employed exactly as in the traditional medicine. Most of the herbal products at present classified as herbal supplements fall into the second and third group: it is apparent that they cannot be considered herbal supplements.