The main adverse effect of insulin is hypoglycemia, which often occurs after too much insulin, not eating on time, or eating too little. Since the main method of insulin is subcutaneous injection, and insulin is an exogenous substance for human body. Therefore, patients may have adverse reactions at the injection site, such as fat accumulation and lumps when fat metabolism occurs. Some patients may also have allergic reactions, such as rash and hives. In addition, because insulin has the effect of slight water and sodium retention, some patients may also develop edema symptoms.