Serotonin (5-hydroxytryptamine, or 5-HT) is a monoamine neurotransmitter synthesised in serotonergic neurons in the central nervous system and enterochromaffin cells in the gastrointestinal tract.

Serotonin is believed to play an important part of the biochemistry of depression, migraine, bipolar disorder and anxiety. It is also believed to be influential on sexuality and appetite.

The name "serotonin" is something of a misnomer and reflects the circumstances of the compound's discovery

In the body, (5-hydroxytryptophan), is synthesized from tryptophan and is a precursor to the neurotransmitter serotonin. Serotonin is found in the brain, blood platelets, and cells of the gastrointestinal tract. Since serotonin is found in the brain and central nervous system it has many implications in cognition, mental health and sleep patterns.