pure encapsulations melatonin-sr | sustained release supplement to support restful sleep and the body's natural sleep/wake cycle* | 60 capsules pure encapsulations melatonin-sr provides sustained-release microactive melatonin to promote healthy sleep. melatonin is a hormone produced by the pineal gland, which regulates the body's sleep/wake cycle. melatonin's primary role is regulation of the body's circadian rhythm, endocrine secretions, and sleep patterns. studies indicate that it facilitates the onset of sleep, as well as sleep efficiency. microactive is an innovative, patented delivery system that offers both improved absorption and sustained release. a pharmacokinetic study of microactive melatonin demonstrated rapid uptake and prolonged presence in plasma up to six hours after a single dose.