Natural Factors L-Tryptophan is a free-form amino acid used as a workout supplement to support muscle repair. L-tryptophan is one of nine essential amino acids, meaning that it cannot be synthesized by the body and must come from the diet. In addition to a healthy, balanced diet and regular resistance training, supplementing with L-tryptophan has been shown to help build lean muscle mass. L-tryptophan is a fundamental component of proteins and has numerous critical roles throughout the body, such as building and repairing muscle and other tissues, maintaining a healthy immune system, producing hormones, and supplying energy. L-tryptophan is also used to synthesize the neurotransmitter serotonin and the hormone melatonin in the brain, which play important roles in mood and sleep. Although various protein-rich foods contain L-tryptophan, the process of absorbing and converting it into a usable form is inefficient. As a free-form amino acid, L-tryptophan is more effective than the form obtained directly from food. By working to restore tryptophan levels and protect muscle integrity during strenuous exercise, L-tryptophan encourages the body to metabolize fat. L-tryptophan is a pharmaceutical-grade, free-form amino acid made through a natural fermentation process. This one-per-day vegetarian capsule is an excellent option for anyone who wants extra nutritional support for their active lifestyle.