melatonin

noun

mel·​a·​to·​nin ˌme-lə-ˈtō-nən How to pronounce melatonin (audio)
: 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
Examples are automatically compiled from online sources to show current usage. Read More Opinions expressed in the examples do not represent those of Merriam-Webster or its editors. Send us feedback.
Johns Hopkins research demonstrates blue light from screens disrupts melatonin production for 2-3 hours after exposure. Charell G. Coleman, Forbes.com, 1 July 2025 The study found that eating two bananas daily increased circulating melatonin levels by more than 500%.7 Plus, the magnesium and potassium in bananas may also be associated with improved sleep.8 Still, more research is necessary to determine bananas’ role in sleep. Amy Brownstein, Verywell Health, 25 June 2025 People spent the bulk of the day outside and didn’t receive any excess light once the sun set, allowing melatonin levels to rise and sleep to take hold. Alex Tzelnic, Outside Online, 22 May 2025 And the in-room dining menu offers snacks to support natural melatonin production. Alisha Prakash, Travel + Leisure, 14 June 2025 See All Example Sentences for melatonin

Word History

Etymology

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.

First Known Use

1958, in the meaning defined above

Time Traveler
The first known use of melatonin was in 1958

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Cite this Entry

“Melatonin.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/melatonin. Accessed 5 Jul. 2025.

Kids Definition

melatonin

noun
mel·​a·​to·​nin ˌmel-ə-ˈtō-nən How to pronounce melatonin (audio)
: a hormone that is secreted by the pineal gland especially in response to darkness and has been linked to the regulation of bodily functions or activities (as sleep) that occur in approximately 24 hour cycles

Medical Definition

melatonin

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