Hormone That Regulates Sleep

This page is the CodyCross answer for the clue below from Inventions, Group 57, Puzzle 4.

Question is: Hormone That Regulates Sleep

and the answer is: MELATONIN

Word Meaning:

MELATONIN — A hormone, related to serotonin, that is secreted by the pineal gland, and stimulates colour change in the skin of reptiles, and is involved in the sleep and wake and reproductive cycles in mammals.

Definitions from Wiktionary.