GlossarySee Full Entry

Serotonin: A hormone found in the brain, platelets, digestive tract and pineal gland. It acts both as a neurotransmitter (a substance that nerves use to send messages to one another) and a vasoconstrictor (a substance that causes blood vessels to narrow). A lack of serotonin in the brain is thought to be a cause of depression.

Alternate Names
5-hydroxytryptamine