Neurotransmitter

A chemical messenger that transmits signals across a synapse from one neuron to another, or from a neuron to a target cell (muscle cell, gland cell). Major neurotransmitters relevant to supplement formulation include acetylcholine (synthesised from choline — Sections 49), dopamine, norepinephrine (synthesised from tyrosine — Section 45), serotonin (synthesised from tryptophan), GABA, and glycine (an inhibitory neurotransmitter in the brainstem and spinal cord — Section 44). The term is often misused in marketing copy — a dietary supplement does not "increase neurotransmitter levels" in any simple or direct way.