Serotonin or 5-hydroxytryptamine (5-HT) is a monoamine neurotransmitter
Monoamine neurotransmitter
thumb|right|350px| A phylogenetic tree showing how a number of monoamine receptors are related to each other.Monoamine neurotransmitters are neurotransmitters and neuromodulators that contain one amino group that is connected to an aromatic ring by a two-carbon chain...

. Biochemically derived from tryptophan
Tryptophan is one of the 20 standard amino acids, as well as an essential amino acid in the human diet. It is encoded in the standard genetic code as the codon UGG...

, serotonin is primarily found in the gastrointestinal (GI) tract, platelets, and in the central nervous system
Central nervous system
The central nervous system is the part of the nervous system that integrates the information that it receives from, and coordinates the activity of, all parts of the bodies of bilaterian animals—that is, all multicellular animals except sponges and radially symmetric animals such as jellyfish...

 (CNS) of animals including humans. It is popularly thought to be a contributor to feelings of well-being and happiness
Happiness is a mental state of well-being characterized by positive emotions ranging from contentment to intense joy. A variety of biological, psychological, religious, and philosophical approaches have striven to define happiness and identify its sources....


Approximately 90% of the human body's total serotonin is located in the enterochromaffin cells in the gut
Gut (zoology)
In zoology, the gut, also known as the alimentary canal or alimentary tract, is a tube by which bilaterian animals transfer food to the digestion organs. In large bilaterians the gut generally also has an exit, the anus, by which the animal disposes of solid wastes...

, where it is used to regulate intestinal movements.