The side effects and bad effects of insulin injection are possible allergy, hypoglycemia, insulin resistance and so on. 1. Allergy: If you are allergic to the insulin agent, it may cause allergic reaction after injection, which may lead to itchy skin, red rash, and in serious cases, angioneurotic edema. 2. Hypoglycemia: If over-injection of insulin may cause transient hypoglycemia, and the patient will have symptoms such as weakness and palpitation. 3. Insulin resistance: generally related to over-injection of insulin, if not pay attention to the dosage, it will cause insulin resistance, resulting in the body’s sensitivity to insulin decreases, and the effect on blood sugar control is not good. Before injecting insulin, you should know that it is forbidden for patients who are allergic to the drug components and hypoglycemic. Long-term use of insulin, in addition to the above several hazards, may also cause ataxia, tachycardia, weight gain and so on. If diabetic patients need to take insulin, they should be under the guidance of a professional physician to avoid unauthorized use of the drug.