mel·​a·​to·​nin | \ ˌme-lə-ˈtō-nən How to pronounce melatonin (audio) \

Definition of melatonin

: a vertebrate hormone that is derived from serotonin, is secreted by the pineal gland especially in response to darkness, and has been linked to the regulation of circadian rhythms

Examples of melatonin in a Sentence

Recent Examples on the Web Candy coated, Fair Trade chocolate—available in milk and dark—is infused with specific ingredients like green tea for energy or melatonin for sleep, for a crunchy chocolate that satisfies both your health needs and sweet cravings. Anna Haines, Forbes, 28 Oct. 2021 There is not enough evidence to support the use of zinc or melatonin in treating the virus. Mckenzie Sadeghi, USA TODAY, 8 Sep. 2021 Study after study says the same thing: the blue light emitted from our phones messes up our melatonin, which is the hormone that regulates our sleep-wake cycle. Elise Taylor, Vogue, 5 Oct. 2021 And a number of studies have detected below-average levels of melatonin in this population. Claudia Wallis, Scientific American, 18 Nov. 2017 Blue light suppresses melatonin levels in the body, which are secreted in a daily 24-hour circadian rhythm typically beginning after dark and peaking between 2 and 4 a.m. Sandee Lamotte, CNN, 14 Mar. 2021 Divij enjoys closing influencer brand deals, scaling his melatonin company, selling houses, and cuddling with his cat. Kara Warner,, 12 July 2021 The idea was to stimulate melatonin secretion and regulate their circadian rhythms. Meeri Kim | Inside Science, ABC News, 11 July 2021 Triggered by darkness, production of melatonin is halted by light. Sandee Lamotte, CNN, 22 Mar. 2021

These example sentences are selected automatically from various online news sources to reflect current usage of the word 'melatonin.' Views expressed in the examples do not represent the opinion of Merriam-Webster or its editors. Send us feedback.

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First Known Use of melatonin

1958, in the meaning defined above

History and Etymology for melatonin

mela-, extracted from Greek melan-, mélās "black, dark" + -tonin (in serotonin); so named because the hormone can lighten skin color in animals by reversing the effect of melanocyte-stimulating hormones — more at melano-

Note: The word was probably introduced in the first published description of the hormone's isolation: Aaron B. Lerner, et al., "Isolation of melatonin, the pineal gland factor that lightens melanocytes," Journal of the American Chemical Society, vol. 80, no. 10 (May 20, 1958), p. 2587.

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The first known use of melatonin was in 1958

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Last Updated

15 Nov 2021

Cite this Entry

“Melatonin.” Dictionary, Merriam-Webster, Accessed 30 Nov. 2021.

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More Definitions for melatonin


mel·​a·​to·​nin | \ ˌmel-ə-ˈtō-nən How to pronounce melatonin (audio) \

Medical Definition of melatonin

: a vertebrate hormone C13H16N2O2 that is derived from serotonin, is secreted by the pineal gland especially in response to darkness, and has been linked to the regulation of circadian rhythms

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