Melatonin SRT provides 6 mg melatonin in a sustained release tablet. The hormone melatonin is secreted by the pineal gland. As a supplement, it is useful for regulating sleep and the body's daily rhythmic cycle, making it ideal for jet lag. Melatonin is also an important antioxidant which acts as an effective scavenger of free radicals. Various factors may cause melatonin levels to become low, such as inadequate dietary intake of its precursors (tryptophan and serotonin), normal aging, insufficient exposure to natural light, and certain medications. Melatonin may support a healthy immune and stress response.