Insulin is a hormone that is needed to convert glucose, starches and other food into energy needed for daily life. Insulin allows cells to use glucose for fuel and is secreted by beta cells in the islets of Langerhans. The release of insulin from the pancreas is stimulated by increased blood glucose, vagal nerve stimulation, and other factors. Insulin is obtained from various animals and available in a variety of preparations. Commercial insulin preparations differ in a number of ways, including differences in the animal species from which they are obtained; their purity, concentration, and solubility; and the time of onset and duration of their biologic action. An oral hypoglycemic agent is not a form of insulin therapy.