A synthetic or animal-derived form of insulin used in the treatment of diabetes mellitus. Therapeutic insulin is formulated to be short-, intermediate- and long-acting in order to individualize an insulin regimen according to individual differences in glucose and insulin metabolism. Therapeutic insulin may be derived from porcine, bovine or recombinant sources. Endogenous human insulin, a pancreatic hormone composed of two polypeptide chains, is important for the normal metabolism of carbohydrates, proteins and fats and has anabolic effects on many types of tissues.