melatonin
noun
mel·a·to·nin
ˌme-lə-ˈtō-nən 
: 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
That sequencing is what protects the melatonin benefit and what most social media posts leave out entirely.
—
Allison Palmer, Miami Herald, 31 Mar. 2026
While the role of supplements like melatonin or vitamin patches is fairly straightforward, NMN is a bit more…complicated.
—Alex Vance, SELF, 31 Mar. 2026
Warm water raises skin temperature, and the core temperature drop after stepping out signals the brain to release melatonin.
—Allison Palmer, Sacbee.com, 31 Mar. 2026
The pineal gland in the brain releases melatonin in response to darkness, which helps regulate your sleep–wake cycle.
—Lindsay Curtis, Verywell Health, 31 Mar. 2026
See All Example Sentences for melatonin
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Allison Palmer, Miami Herald, 31 Mar. 2026
While the role of supplements like melatonin or vitamin patches is fairly straightforward, NMN is a bit more…complicated.
—Alex Vance, SELF, 31 Mar. 2026
Warm water raises skin temperature, and the core temperature drop after stepping out signals the brain to release melatonin.
—Allison Palmer, Sacbee.com, 31 Mar. 2026
The pineal gland in the brain releases melatonin in response to darkness, which helps regulate your sleep–wake cycle.
—Lindsay Curtis, Verywell Health, 31 Mar. 2026
See All Example Sentences for melatonin
Cite this Entry
“Melatonin.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/melatonin. Accessed 5 Apr. 2026.
Copy CitationKids Definition
melatonin
noun
mel·a·to·nin
ˌmel-ə-ˈtō-nən
: 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
: 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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