Stimulants, also known as excitants and hypersthenics, are medicinal substances capable of exciting a temporary and rapid exaltation of the organic actions, the excitation thus produced being extended or not to the rest of the system. Although the stomach is the organ generally selected in medical practice to be the first impressed by stimulants, on account of the extensive sympathy which exists between it and the rest of the system, in dental practice these agents are topically applied to the mucous membrane of the mouth as counter-irritants and vesicants. The influence of stimulants is most apparent in conditions of morbid depression, whereas in health they soon induce depression. They possess the power of arousing the energies of the nervous system, and hence are beneficial in many nervous disorders, especially those of a spasmodic nature. When applied to the gastro-intestinal canal they promote digestion as stomachics, and when administered to dispel flatulence they are known as carminatives. When internally administered, it is for the most part advisable to begin with small doses, and increase them as circumstances may require. In some cases, however, it is necessary to give them freely from the first. It is often requisite to change the stimulating substance and also the part of the body to which it is applied; when the stomach fails, the rectum and skin may be acted upon beneficially. Topically applied, stimulants irritate and inflame the parts with which they come in contact, and are then known as irritants.

The most powerful and rapid stimulants are known as diffusible, while others of a vegetable nature, containing a volatile oil, are termed aromatic. Among the class of diffusible stimulants are such agents as alcohol, preparations of ammonia, arnica, phosphorus, etc., etc. Among the class of aromatic stimulants are capsicum, cinnamon, black pepper, mace, cloves, pimento, oil of turpentine, ginger, cardamom, calamus, gaultheria, peppermint, origanum, etc., etc.