Like other amino acids, L-Tryptophan is one of the building blocks of protein, but unlike some amino acids, L-Tryptophan is considered essential because the body cannot manufacture its own. L-Tryptophan plays many roles in animals and humans alike, but perhaps most importantly, it is an essential precursor to a number of neurotransmitters in the brain. As such, L-Tryptophan is the only substance normally found in the diet that can be converted into serotonin. Since serotonin, in turn, is converted in the brain into melatonin, L-Tryptophan clearly plays a role in balancing mood and sleep patterns.