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Acetylcholine is synthesized by choline acetyltransferase, stored in vesicles, released in response to calcium, and rapidly hydrolyzed by acetylcholinesterase. Its actions depend on muscarinic GPCRs and nicotinic ligand-gated ion channels, including ganglionic and neuromuscular-junction subtypes. The drug groups in this topic include direct muscarinic agonists, reversible and irreversible acetylcholinesterase inhibitors, antimuscarinics, ganglionic blockers, and neuromuscular blockers. The source highlights clinically important contrasts, such as physostigmine’s ability to cross the blood–brain barrier and the timing-sensitive use of pralidoxime in organophosphate poisoning. It also introduces characteristic toxicity patterns and important neuromuscular-blocker risks. Together, these mechanisms provide a framework for comparing drug actions, uses, and adverse effects.