Atropine inhibits the muscarinic actions of acetylcholine on structures innervated by postganglionic cholinergic nerves, and on smooth muscles which respond to endogenous acetylcholine but are not so innervated. As with other antimuscarinic agents, the major action of atropine is a competitive or surmountable antagonism which can be overcome by increasing the concentration of acetylcholine at receptor sites of the effector organ (e.g., by using anticholinesterase agents which inhibit the enzymatic destruction of acetylcholine). The receptors antagonized by atropine are the peripheral structures that are stimulated or inhibited by muscarine (i.e., exocrine glands and smooth and cardiac muscle). Responses to postganglionic cholinergic nerve stimulation also may be inhibited by atropine but this occurs less readily than with responses to injected (exogenous) choline esters. Atropine is relatively selective for muscarinic receptors. Its potency at nicotinic receptors is much lower, and actions at non-muscarinic receptors are generally undetectable clinically. Atropine does not distinguish among the M1, M2, and M3 subgroups of muscarinic receptors.

Atropine-N-oxide hydrochloride is an alkaloid of the belladonna plants. It is the major metabolite of atropine. It is a competitive nonselective antagonist at central and peripheral muscarinic acetylcholine receptors.

Methylatropine (methylatroponium) is a belladonna derivative. In 1902 the Bayer Company introduced atropine methonitrate, a quaternary ammonium salt of atropine (Eumydrin), as a mydriatic for dilation of the pupil during ophthalmic examination. Due to its highly polar nature it penetrates less readily into the central nervous system than atropine and was therefore introduced for relieving pyloric spasms in infants. Atropine methyl nitrate is a muscarinic acetylcholine receptor antagonist that does not cross the blood-brain barrier. Atropine methyl nitrate has been used for its peripheral muscarinic effects (targeting the bladder, respiratory tract, and to block parasympathetic signaling to the heart, among others) and to separate central from peripheral nervous system effects, or to protect against peripheral side effects when using muscarinics that do cross the blood brain barrier.

Methylatropine (methylatroponium) is a belladonna derivative. In 1902 the Bayer Company introduced atropine methonitrate, a quaternary ammonium salt of atropine (Eumydrin), as a mydriatic for dilation of the pupil during ophthalmic examination. Due to its highly polar nature it penetrates less readily into the central nervous system than atropine and was therefore introduced for relieving pyloric spasms in infants. Atropine methyl nitrate is a muscarinic acetylcholine receptor antagonist that does not cross the blood-brain barrier. Atropine methyl nitrate has been used for its peripheral muscarinic effects (targeting the bladder, respiratory tract, and to block parasympathetic signaling to the heart, among others) and to separate central from peripheral nervous system effects, or to protect against peripheral side effects when using muscarinics that do cross the blood brain barrier.

Xenytropium is a quaternary ammonium derivative of atropine. It combines antimuscarinic and ganglionic blocking potencies. It was marketed in Eastern Europe under trade name Gastripon for the treatment of gastritis, gastric and duodenal ulcers, gallstone diseases, and other conditions.