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Serotonin

Serotonin is a hormone found in the brain, platelets, digestive system and the pineal gland (a small gland in the brain). It acts as a chemical messenger, sending messages between nerves (neurotransmitter). It also sends messages to make blood vessels narrower. Some carcinoid tumours make serotonin and high levels in the body can cause diarrhoea, wheezing and flushing.

Updated: 17 January 2012