In medicine, cholinesterase inhibitors are "drugs that inhibit cholinesterases. The neurotransmitter acetylcholine is rapidly hydrolyzed, and thereby inactivated, by cholinesterases. When cholinesterases are inhibited, the action of endogenously released acetylcholine at cholinergic synapses is potentiated. Cholinesterase inhibitors are widely used clinically for their potentiation of cholinergic inputs to the gastrointestinal tract and urinary bladder, the eye, and skeletal muscles; they are also used for their effects on the heart and the central nervous system."
Cholinesterase inhibitors may stimulate the parasympathetic nervous system.
They were first synthesized industrially as insecticides, and still are used as highly potent insect killers, although too toxic for general use. Their toxicity is exploited as chemical weapons; the class of "nerve gases" are cholinesterase inhibitors.