Written by the Fiveable Content Team • Last updated September 2025
Verified for the 2026 exam
Verified for the 2026 exam•Written by the Fiveable Content Team • Last updated September 2025
Definition
Melatonin is a hormone produced by the pineal gland in the brain. It helps regulate sleep-wake cycles, also known as circadian rhythms.
Related terms
Pineal Gland: A small endocrine gland in the vertebrate brain which produces melatonin.
Circadian Rhythms: Physical, mental, and behavioral changes that follow a daily cycle; they respond primarily to light and darkness in an organism's environment.
Endocrine System: The collection of glands that produce hormones that regulate metabolism, growth and development, tissue function, sexual function, reproduction, sleep, and mood among other things.