Serotonin, or 5-hydroxytryptamine [5-HT], is a biogenic amine implicated in controlling feeding behavior, thermoregulation, sexual behavior, and sleep. 5-HT receptors recognize at least three types of molecular structures: G protein coupled receptors, ligand gated ion channels, and transporters. It is now believed that there are at least seven different families of receptors, many of which have subtypes. The nervous system can be compared to a group of well-modulated neural networks functioning in parallel. The serotonergic system may modulate these networks rather than actually mediate individual responses. Circumstantial evidence suggests a link between 5-HT and migraine. Platelet HT decreases during an attack, and in some cases increased levels of metabolites are found. Many antimigraine drugs interact with 5-HT and its receptors.