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How does ZzzQuil Work? Article

DIPHENHYDRAMINE HCL & HOW
ZZZQUIL WORKS

ZzzQuil contains diphenhydramine HCl, which is a big word for a small compound that helps you sleep. To help you stay awake and alert, your body produces histamine, a naturally occurring substance that interacts with receptors in your brain to promote wakefulness.

Diphenhydramine HCI is an antihistamine which blocks the affects of histamine to help you fall asleep faster.