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

Dark cherries with nuts also help boost melatonin production. —Faye Remedios, Glamour, 9 Apr. 2025

While blue light can delay melatonin production, my team’s research and that of others suggests that the way people interact with social media may play an even bigger role in sleep disruption. —Brian N. Chin, The Conversation, 8 Apr. 2025

Tart cherry juice is a natural source of melatonin, a hormone that helps regulate sleep. —Elizabeth Fogarty, Better Homes & Gardens, 8 Apr. 2025

The mean melatonin dose ranged from 1.6 to 4.4 mg.6 Jet lag: In a review, study participants took 0.5 to 5 mg of melatonin close to the target bedtime of the final destination. —Allison Herries, Verywell Health, 31 Mar. 2025

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

Rhymes for melatonin

• calcitonin
• digitonin
• serotonin
• kronen
• onan
• phonon
• ronin
• santonin

Kids 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