WHAT IS TRYPTOPHAN? Tryptophan is one of eight essential amino acids – essential means the body can’t produce Tryptophan itself & it must be obtained via the diet. Tryptophan is best known for being a precursor of both Serotonin & Melatonin. Tryptophan can be found in foods such as meat, fish & dairy. BULK POWDERS™ Tryptophan is comprised of 100% Tryptophan powder. A quick check of the Certificate of Analysis (COA) on this product page (to the side of the product image)