Insulin is a peptide hormone secreted by the pancreas to decrease blood glucose in response to high glucose levels in the blood, also regulating the metabolism of carbohydrates and fats. Works in opposition to glucagon, and also inhibits the production of glucose by the liver. Patients with metabolic disorders like with type I and type II diabetes mellitus and metabolic syndrome either do not have a constant proportion of insulin in the blood or are insensitive to its effects. Insulin is commonly used medically to treat some forms of diabetes.