In the human pancreas, there are numerous “islands” of different shapes, which are medically known as “islets”. Insulin is the only hormone in the body that can lower blood sugar. The regulation of insulin secretion is very precise. After the blood glucose rises, such as after a meal, the B cells of the pancreatic islets respond quickly and secrete the corresponding insulin into the blood circulation, and under the action of insulin, the liver, fat and muscle tissue speed up the uptake of glucose from the blood, so that the elevated blood glucose returns to the fasting level within 2 to 3 hours. Insulin secretion decreases after blood glucose drops to avoid hypoglycemia. Insulin was discovered in 1921 by a Canadian doctor named Banting and his colleagues. The discovery of insulin and its subsequent rapid development and application revolutionized the fate of diabetic patients and ushered in a new era of diabetes treatment. A wide range of insulin products have been developed for clinical use. In terms of the source of insulin, there are animal insulins, genetically engineered human insulins and insulin analogues. The former can be used for subcutaneous and intravenous injections, while the latter two can only be used for subcutaneous injections. In addition, there are also mixtures of short-acting and medium-acting insulins, which are available in various dosage forms in different combinations. So, under what circumstances do diabetic patients need insulin injections? A brief summary is as follows: Patients with type 1 diabetes require replacement therapy for life. These patients have very limited or even complete loss of functional B cells in the islets, and treatment with insulin is necessary to maintain life and is an absolute indication, with no other options available. Secondly, diabetes combined with pregnancy, or during pregnancy, elevated blood glucose is called gestational diabetes, because oral hypoglycemic drugs may have adverse effects on fetal development, it is also necessary to control blood glucose with insulin. For those who need to breastfeed after delivery, if their blood sugar is still high, they should also control their blood sugar with insulin throughout the breastfeeding period. Patients with type 2 diabetes should consider insulin therapy in the following cases Failure of oral hypoglycemic drugs, relatively serious infection, trauma, before and after surgery, fever. Other serious clinical conditions such as myocardial infarction, stroke, diabetic ketoacidosis, hyperglycemic hyperosmolar state. Some patients with type 2 diabetes who have been ill for more than 10 to 15 years, as the function of pancreatic B-cells has gradually gone into failure, then they are similar to the situation of type 1 diabetes and also need insulin to control blood sugar. As mentioned above, there are many types of insulins, and the specific clinical application should be selected according to the condition. Short-acting and fast-acting insulins are used to control blood sugar after meals and are often injected before meals, while medium- and long-acting insulins are used to control blood sugar at night and are often injected at night before bedtime. Insulin can also be used in combination with oral hypoglycemic drugs, and this method is widely used in clinical practice. Remember: Patients are advised not to inject insulin on their own without doctor’s guidance to avoid causing hypoglycemia or other unpredictable situations.