ZzzQuil is a non-habit forming sleep-aid for the relief of occasional sleeplessness. It reduces time to fall asleep if you have difficulty falling asleep. The active ingredient in ZzzQuil is diphenhydramine HCl, which is an antihistamine. The brand, which is a sub-brand of Vicks, was created and made widely available in the summer of 2012. ZzzQuil is not for colds, not for pain, but just for sleep.