Antagonists are drugs which are opposed to each other in their physiological effects.

Antagonism was formerly known as "therapeutic incompatibility," but, as this latter term has led to confusion, it is now thought best to limit the term "incompatibility" to chemical and physical changes, such as may occur in a prescription, and to give the term "antagonism "to physiological opposition.

No general rule can be laid down for the avoidance of antagonism. Some of our most valuable drugs contain active principles which are physiologically opposed to each other in their action;

instance: jaborandi, which contains two absolutely antagonistic alkaloids, pilocarpine and jaborine, the latter in small quantity, yet sufficient to control the action of the former.

Opium is a conspicuous example of a complex remedy, containing, besides gum, sugar, etc., eighteen different alkaloids, two neutral principles, and two peculiar acids; so that a prescriber of this drug, while he may, perhaps, flatter himself that he is conforming strictly to the present notions of pharmaceutical simplicity, is in effect a polypharmacist of most pronounced type. Moreover, not only are the constituents of opium very numerous, but, like others mentioned, the drug affords in its thebaine and morphine a further illustration of direct physiological antagonism.

Again, physiological antagonists are often given together, as atropine and morphine, or aconite and digitalis in certain cases of cardiac arrhythmia.

The author cannot too strongly recommend that physicians ignorant of the physiological action of drugs in large and small doses, if they prescribe at all, should avoid including many remedies in one prescription. But, given a competent and thorough knowledge of the action of drugs and the exact condition of the patient, the physician is justified in giving one or twenty drugs in the same prescription, since he is perfectly familiar with the several agents of relief, and can foretell with nicety the effect to be produced by their combination. In all cases a physician should be as certain of the action and strength of the preparations he administers as the surgeon of the aseptic condition of his hands and instruments.