Melatonin appears to be the primary sleep-regulating hormone of the body. It has been used by individuals suffering from insomnia, particularly when adjusting to shift-work cycles or jet lag. In the US Melatonin is available over-the-counter, however, it may require a prescription in some countries. Most Popular Types: Nature's Bounty Melatonin, Melatonin Time Release, Natrol Melatonin,