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[Biochemistry](https://durgical.com/en/biochemistry/) · Molecule

# Melatonin

Melatonin is the pineal hormone of darkness. It rises at night and tells the body's clock that it is time to sleep.

Updated 2026-11-01

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## Key facts

- Made in the pineal gland from serotonin by AANAT (acetylation) and ASMT (methylation with SAM).
- Darkness signals from the retina reach the pineal through the suprachiasmatic nucleus and sympathetic nerves; light stops synthesis.
- It acts on MT1 and MT2 receptors, mainly in the suprachiasmatic nucleus.
- The liver clears it quickly (6-hydroxylation by CYP1A2).

**Formula**
C₁₃H₁₆N₂O₂

**PubChem**
[CID 896](https://pubchem.ncbi.nlm.nih.gov/compound/896)

## Structure

- Serotonin with an acetyl group on the amine and a methyl on the 5-hydroxyl (N-acetyl-5-methoxytryptamine).

## Clinical notes

- Melatonin and its agonists are used for jet lag and some sleep-onset problems.
- Night-time light and shift work suppress its rise.
- Beta-blockers can lower night-time melatonin because the pineal signal is β-adrenergic.

## Drugs that act here

- [Melatonin](https://durgical.com/en/pharmacology/melatonin/)
- [Ramelteon](https://durgical.com/en/pharmacology/ramelteon/)

## Pathways

- [Serotonin and melatonin synthesis](https://durgical.com/en/biochemistry/pathways/serotonin-and-melatonin-synthesis/)

## Related

- [Serotonin (5-hydroxytryptamine)](https://durgical.com/en/biochemistry/molecules/serotonin/)
- [Tryptophan](https://durgical.com/en/biochemistry/molecules/tryptophan/)
- [S-adenosylmethionine (SAM)](https://durgical.com/en/biochemistry/molecules/s-adenosylmethionine/)
- [Acetyl-CoA](https://durgical.com/en/biochemistry/molecules/acetyl-coa/)

## Test yourself

Think of the answer, then tap the question to see it.

## Which gland makes melatonin, and when?

The pineal gland, mostly at night in darkness.

## Which two enzymes turn serotonin into melatonin?

AANAT, which adds an acetyl group, and ASMT, which adds a methyl group from SAM.

## Why does light at night lower melatonin?

Light reaches the suprachiasmatic nucleus through the retina and stops the sympathetic signal that activates AANAT.

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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: [Melatonin (CID 896)](https://pubchem.ncbi.nlm.nih.gov/compound/896) (PubChem, NCBI, 2026) · Public domain; [Acetylserotonin O-methyltransferase (ASMT) - Homo sapiens](https://www.uniprot.org/uniprotkb/P46597/entry) (UniProt, 2026); Textbook of Biochemistry for Medical Students, 6th ed. (Jaypee Brothers Medical Publishers (Vasudevan DM, Sreekumari S, Vaidyanathan K), 2011).

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Representative model, for educational purposes only.

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Source: https://durgical.com/en/biochemistry/molecules/melatonin/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/biochemistry/molecules/melatonin/