NOW Foods - Melatonin Sustained Release Healthy Sleep Cycle Support 5 mg. - 120 Tablets Melatonin is a potent free radical scavenger naturally produced in the pineal gland and present in high amounts in the gastrointestinal tract. It is involved in many of the body, brain and glandular biological functions including regulation of normal sleep/wake cycles, regulation of the immune system and maintenance of a healthy gastrointestinal lining.