Chronobiotic is a substance that is capable of therapeutically re-entering short - term dissociated or long - term desynchronized circadian rhythms

Circadian rhythm

A circadian rhythm, popularly referred to as body clock, is an endogenously driven , roughly 24-hour cycle in biochemical, physiological, or behavioural processes. Circadian rhythms have been widely observed in plants, animals, fungi and cyanobacteria...

, or prophylactically preventing their disruption following an environmental insult. In more simple words, chronobiotic is defined as the agent causes phase adjustment of the body clock. The most widely recognized chronobiotic is melatonin

Melatonin

Melatonin , also known chemically as N-acetyl-5-methoxytryptamine, is a naturally occurring compound found in animals, plants, and microbes...

.