1) A neurotransmitter. Acetylcholine in vertebrates is the major transmitter at neuromuscular junctions, autonomic ganglia, parasympathetic effector junctions, a subset of sympathetic effector junctions, and at many sites in the central nervous system. It is generally not used as an administered drug because it is broken down very rapidly by cholinesterases, but it is useful in some ophthalmological applications.

2) A neurotransmitter C₇H₁₇NO₃ released at autonomic synapses and neuromuscular junctions, active in the transmission of nerve impulses, and formed enzymatically in the tissues from choline.