After feasting on your Thanksgiving dinner today, a specific word may come to mind: tryptophan. Tryptophan is an amino acid found in high levels in turkey. The main reason for the association between tryptophan and drowsiness is that tryptophan is a chemical precursor to melatonin, a neurotransmitter that plays a role in regulating the circadian cycle, the regular changes in mental and physical characteristics that occur over the course of 24 hours. Indeed, purified tryptophan is a mild sleep-inducing agent [1].