Melatonin sleep hormone, molecular model. Melatonin is part of the control system of the sleep-wake cycle and of vertebrate circadian rhythms. It is a hormone produced by the pineal gland. Melatonin is a common dietary supplement for insomnia and jet lag. Atoms are colour-coded: carbon is black; hydrogen is white; fluorine is green; nitrogen is blue; oxygen is red; sulphur is yellow.