Melatonin is a slightly off-white, odourless crystalline powder. It is very slightly soluble in water and in dilute hydrochloric acid. 

Melatonin is a small molecule, a derivative of the amino acid tryptophan, N-acetyl-5 methoxytryptamine. It is a potent hormone with well-recognized activities and the potential to influence many bodily functions. It is produced by the pineal gland in the brain and is secreted when the body recognizes darkness. Melatonin has intense effects on the timing of the sleep/awake cycle, regulating the circadian rhythms of several biological functions. This is its most studied biological activity. Melatonin, as a multifunctional hormone, appears to regulate or modulate other functions in humans through the activation of its receptors and works as a strong antioxidant that protects the DNA. Melatonin’s antioxidant activity may reduce Parkinson’s disease development, prevent cardiac arrhythmia, and, in animals, promote longevity.