Herbal medicine is the use of medicinal plant material in the treatment of disease. Plants are a complex mixture of organic components, and the actions of a plant medicine are often multi-modal, meaning that they can have more than one action when used as medicine.
Herbs are classified in the Western model of herbal medicine by their medicinal actions on the body eg. bitters, diuretics, circulatory stimulants. This classification is the result of clinical experience with the herbal medicines.
One of the advantages of this system is that an herb can be in more than one category, and may be selected for you on an individual basis according to your specific situation.