 Melatonin has been established as a reliable output of the SCN's timekeeping property, and melatonin research has been coupled with SCN research since 1974.Because melatonin is secreted according to signals to the pineal gland from the SCN, exogenous melatonin taken as a chronobiotic can affect feedback to the SCN and its subsequent circadian rhythms.Quiadon was one of the first chronobiotics used to affect circadian rhythms in humans.