Alteratives are medicinal substances which are capable, when administered in small doses, of removing morbid structures and conditions, without any sensible evacuation; in other words, changing, in some inexplicable and insensible manner, certain morbid actions of the system.

Alterative remedies re-establish the healthy functions of the animal economy in a slow but decided manner, acting on the various secreting organs, sometimes without any sensible increase of the secretions themselves. The effect of minute doses of mercury, iodine and other substances, upon the glandular apparatus, affords examples. Medicinal remedies of almost every class become alteratives by being administered in very small doses, at intervals of a few hours; and they are generally classed with stimulants and tonics, and some of them with narcotics. By their action the secretions and exhalations are increased; the exudation of plastic or coagulable lymph is diminished; the formation of false membranes checked ; the textures softened; inflammatory action arrested; and morbid growths and deposits absorbed. Phlegmonous inflammation is arrested, and visceral and glandular enlargements are dispelled. But if administered too freely, the blood may become so impoverished as to interfere with the functions of nutrition, and a marasmatic or cachetic condition be produced, the textures being softened, or even destroyed. Hence this class of remedies should be carefully administered, and their effects be closely observed. The chief use of alteratives is antiphlogistic or resolvent; for example, the mercurials are generally employed in acute inflammation, and the preparations of iodine and bromine in chronic inflammations.

Included in this class are the preparations of mercury, iodine, iodide of potassium, iodoform, bromine preparations of arsenic, phosphate and hypophosphite of lime, chlorate of potassium, permanganate of potassium, chlorine water, chlorinated lime, etc., etc.