Melatonin (CAS 73-31-4) is N-acetyl-5-methoxytryptamine, an indoleamine with formula C13H16N2O2 and molecular mass 232.28 g/mol. It is produced mainly by the pineal gland and functions as a hormone involved in circadian timing and sleep–wake signaling. Its actions include signaling through MT1 and MT2 receptors. Commercial reference materials are commonly described as white to off-white crystalline solids; confirm appearance, identity, assay, and any other specification against the lot-specific certificate of analysis rather than assuming all grades are interchangeable.
The compound is used in laboratory studies of circadian biology and melatonin-receptor signaling, and as an analytical reference where suitable. Melatonin is also marketed as an ingredient in some regulated products, but availability, permitted uses, classification, and claims vary by jurisdiction.