Branched-chain amino acids are essential amino acids in which the chemical configuration has a branched shape. Tryptophan, an amino acid precursor of serotonin, is thought to play a role in the pathogenesis of cancer anorexia. Uptake of tryptophan into the brain is regulated by a specific transport system, which is competitively shared with the other amino acids, branched-chain amino acids. By administering oral branched-chain amino acids, the desired result would be a reduced level of tryptophan concentrations in the brain, limiting its anorexic effects. Branched-chain amino acids include leucine, isoleucine, and valine. These are available without a prescription as dietary supplements. Effects have been examined related to anorexia.