Biochemistry · Molecule
Serotonin (5-hydroxytryptamine) !
Serotonin is made from tryptophan. It is a brain neurotransmitter for mood and sleep, and in the gut it controls motility.
Updated 2026-11-01
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Key facts
- Tryptophan hydroxylase (BH4) and aromatic L-amino acid decarboxylase (B6) make it.
- About 90% is in enterochromaffin cells of the gut; platelets take it up and carry it.
- MAO-A breaks it down to 5-HIAA, which is excreted in urine.
- In the pineal gland it is the precursor of melatonin.
- Also called
- 5-HT
- Formula
- C₁₀H₁₂N₂O
- PubChem
- CID 5202
Structure
- An indole ring with a 5-hydroxyl and an ethylamine side chain.
Clinical notes
- Carcinoid syndrome: tumour serotonin causes flushing, diarrhoea and right-heart valve fibrosis; urinary 5-HIAA is high.
- SSRIs raise synaptic serotonin and are first-line antidepressants.
- Serotonin syndrome (agitation, clonus, fever) appears when serotonergic drugs are combined, for example with MAO inhibitors.
- 5-HT₃ antagonists such as ondansetron prevent chemotherapy-induced vomiting.
Drugs that act here
Pathways
Related conditions
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Test yourself
Think of the answer, then tap the question to see it.
From which amino acid is serotonin made?
Tryptophan, by tryptophan hydroxylase and then aromatic L-amino acid decarboxylase.
Where is most of the body's serotonin?
In the enterochromaffin cells of the gut, about 90%; platelets carry it in the blood.
Which urinary product of serotonin is high in carcinoid syndrome?
5-HIAA (5-hydroxyindoleacetic acid).
Molecules are shown in their neutral form, as the databases deposit them; in the cell the acids and phosphates are ionised.
Educational information, not medical advice. For any symptom, see a health professional.
Sources: Serotonin (CID 5202) (PubChem, NCBI, 2026) · Public domain; 5-HIAA urine test: MedlinePlus Medical Encyclopedia (MedlinePlus, US National Library of Medicine, 2026); Textbook of Biochemistry for Medical Students, 6th ed. (Jaypee Brothers Medical Publishers (Vasudevan DM, Sreekumari S, Vaidyanathan K), 2011).
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