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
Scheer’s research suggests melatonin—a hormone your body secretes at night to help prepare for sleep—plays a role.
—
Jamie Ducharme, Health, 10 Feb. 2026
The circadian rhythm, the body’s natural alarm clock that will suppress melatonin in the morning and increase alertness, is triggered by sunlight.
—Alexa Mikhail, Flow Space, 4 Feb. 2026
How Melatonin and Magnesium Work Together Some sleep-support supplements contain both melatonin and magnesium.
—Trang Tran, Verywell Health, 4 Feb. 2026
That being said, one serving of this spray has 3 milligrams of melatonin, which takes about six pumps to dispense.
—Julia Forbes, Wired News, 31 Jan. 2026
See All Example Sentences for melatonin
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Jamie Ducharme, Health, 10 Feb. 2026
The circadian rhythm, the body’s natural alarm clock that will suppress melatonin in the morning and increase alertness, is triggered by sunlight.
—Alexa Mikhail, Flow Space, 4 Feb. 2026
How Melatonin and Magnesium Work Together Some sleep-support supplements contain both melatonin and magnesium.
—Trang Tran, Verywell Health, 4 Feb. 2026
That being said, one serving of this spray has 3 milligrams of melatonin, which takes about six pumps to dispense.
—Julia Forbes, Wired News, 31 Jan. 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 14 Feb. 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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