parasympathomimetic

A parasympathomimetic is a drug that imitates the parasympathetic nervous system, switching the body into rest-and-digest mode. Expect the cholinergic signature: slower heart, more saliva and tears, smaller pupils, busier gut, and a contracting bladder.

There are two routes to this effect. Direct-acting agents are muscarinic agonists that bind and activate muscarinic receptors themselves, such as pilocarpine and bethanechol. Indirect-acting agents are cholinesterase inhibitors, which do not touch the receptor but block the enzyme that destroys acetylcholine, letting the body's own transmitter build up and act longer.

Clinically they are used where cholinergic stimulation helps: pilocarpine for glaucoma and dry mouth, bethanechol for urinary retention after surgery, and cholinesterase inhibitors for myasthenia gravis and to reverse neuromuscular blockade. The downside is overshoot, producing the so-called SLUDGE effects of excessive secretion, gut cramping, and slow heart.