Amino acids are the subunits that make up proteins. They are necessary for the function of all cells, for tissue repair, and for the production of enzymes and neurotransmitters. The body uses 20 amino acids to construct proteins, but nine "essential amino acids" cannot be made by the human body and must be supplied by the diet in order to achieve proper protein synthesis and maintain overall health. People with limited diets or poor digestion may not get enough essential amino acids from their diet. In contrast to proteins or peptide-bound amino acids, Now Amino-9 Essentials contains all 9 essential amino acids in their superior free-form state and in the proportions recommended by the National Academy of Sciences to optimize protein synthesis and tissue repair for adults age 19 and over.