Insulin is a protein hormone secreted by pancreatic beta cells in the pancreas stimulated by endogenous or exogenous substances such as glucose, lactose, ribose, arginine, and glucagon. Insulin is the only hormone in the body that lowers blood glucose while promoting glycogen, fat, and protein synthesis. Exogenous insulin is mainly used for diabetes treatment. So when to start insulin application? 1. Temporary use of insulin is needed to tide over the dangerous period when there is a serious acute complication or stress state. Non-ketotic hyperosmolar coma, lactic acidosis, ketoacidosis, severe infection, etc. 2.When there are serious chronic complications. Such as severe diabetic nephropathy, diabetic foot, etc. 3.Newly diagnosed diabetic patients with wasting that are difficult to differentiate from type 1 diabetes should use insulin as the first-line drug. 4.Insulin should be used as early as possible to treat weight loss without obvious cause in the course of diabetes. 5.Gestational diabetes mellitus. 6.Secondary diabetes mellitus and atopic diabetes mellitus. 7, Combination of some other serious diseases such as coronary heart disease, cerebrovascular disease, hematological disease, liver disease, collagen disease (lupus erythematosus, nodular arteritis, scleroderma, rheumatoid), etc. In short, insulin is the best choice for many people, including newly diagnosed type 2 diabetic patients. Doctors often feel that patients are more afraid of injections, so they usually recommend it only as a last resort. But insulin does have many advantages that oral medications cannot achieve, such as: faster action, better results, finer dose adjustment, and no unknown adverse effects.