Cholinergic drugs are medications that mimic the action of acetylcholine, a neurotransmitter in the nervous system. These drugs can be divided into two categories: direct-acting agents that stimulate cholinergic receptors and indirect-acting agents that inhibit acetylcholinesterase, an enzyme that breaks down acetylcholine. They are used to treat a variety of conditions by enhancing the parasympathetic nervous system functions.