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).

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

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.

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.

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) (PubChem, NCBI, 2026) · Public domain; Acetylserotonin O-methyltransferase (ASMT) - Homo sapiens (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.