Also known as 5-hydroxytryptamine (5-HT), a compound derived from the amino acid tryptophan, that affects the diameter of blood vessels and also functions as a neurotransmitter. Serotonin is released by mast cells, basophils, and platelets, and acts as a mediator of inflammation and allergic reactions. It plays an important role in blood clotting, stimulating a strong heart beat, initiating sleep, fighting depression (prescription drugs that treat depression raise the brain's levels of serotonin), and causing migraine headaches in susceptible individuals (because of its ability to constrict blood vessels or cause them to spasm).
