Doctor s Best L-Tryptophan is an essential amino acid (protein building block) in human nutrition that helps promote healthy sleep. Essential amino acids are not synthesized by the body and must be obtained in the diet. Doctor?s Best L-Tryptophan with TryptoPure? is manufactured and tested for purity according to the Japanese Pharmacopeia (JP) and the United States Pharmacopeia (USP) standards.* At Doctor?s Best we lead with science. Our products are backed by research and crafted using pure ingredients carefully sourced from around the globe. Since 1990 we have dedicated ourselves to providing highly effective nutritional supplements that enable you to live a healthier lifestyle. We want nothing more than to see you and your family thrive!