Insulin drugs have certain harmful effects on the body, such as hypoglycemic reaction, allergic reaction and other adverse reactions. 1. Hypoglycemic reaction: it is the most common adverse reaction that occurs when patients apply insulin. Usually insulin has the effect of lowering blood glucose, and when the dose is too large, patients may experience hypoglycemic reaction, which is usually manifested as dizziness, nausea, vomiting and so on. In serious cases, it may lead to coma. 2. Allergic reaction: redness, swelling or itching may occur at the injection site, which can usually be relieved by itself. Insulin is suitable for diabetic patients who need to use insulin to maintain blood glucose level, hypoglycemia, allergic to insulin is prohibited. When patients use insulin, they should follow the advice of professional doctors, and should not use the medicine privately to avoid adverse consequences.