Serotonin Precursor Dietary Supplement Plant Based L-Tryptophan The stress of living in a fast-paced world with demands of work and family may sometimes leave you feeling tense, anxious and unable to be your best. Perhaps you've got too much on your mind, affecting your sleep, confidence and concentration. L-Tryptophan is an essential amino acid that serves as a precursor to the important neurotransmitter serotonin. L-Tryptophan is an essential amino acid found in many protein foods including: turkey, fish, nuts, beans, dairy and eggs. Because it cannot be synthesized by the body, L-Tryptophan is obtained in the diet. In the body it functions as a precursor to serotonin, a neurotransmitter. To help assure the purity and potency of every vegetarian capsule, Natural Balance uses pharmaceutical grade L-Tryptophan. Discover Natural Balance Since 1983, Natural Balance has energized people's health and well-being by offering specialty supplements. Scientifically blending select high-quality ingredients into proprietary formulas is our art. Helping people live healthier, more enjoyable lives is our passion.