Understanding the Side Effects of Insulin

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Taking insulin will help you better control your blood glucose levels and reduce your risk for complications from diabetes. However, like other drugs, insulin can cause side effects. Here are some to watch out for. If you experience any of the side effects below, talk with your doctor to come up with the best solution, while keeping your diabetes under control.


Hypoglycemia, or low blood glucose, is one of the most common side effects of insulin therapy. It can occur when insulin lowers glucose levels too much. Symptoms of hypoglycemia include dizziness, shaking, sweating, hunger, sudden changes in mood, difficulty concentrating, and even seizure or loss of consciousness. Hypoglycemia is a true medical emergency and urgent steps to restore blood glucose levels are required whenever it occurs.

You may be able to reduce your risk for hypoglycemia by frequently checking your blood glucose levels and working with your doctor to determine the best insulin doses and delivery method for you.

Weight Gain

In some instances, taking insulin may contribute to weight gain. Insulin can affect how your brain experiences hunger. You may notice changes in your appetite and cravings. If you frequently experience hypoglycemia, taking in more carbohydrates to control your glucose levels could also lead to extra pounds. It can become a seesaw of weight gain and loss, but you have the ability to jump off!

Discuss any weight gain with your doctor. You may also consider working with a registered dietitian, who can help you change your diet to aid weight loss.


Insulin helps move potassium into cells. This can lead to hypokalemia, or low potassium levels in the blood. Untreated, the condition can cause problems with breathing and heart function—and even death.

You are most sensitive to this side effect if you’re already at risk for hypokalemia because you take potassium-lowering medications, such as diuretics (fluid pills). Always be sure to let your doctor know which prescription and over-the-counter medications you take.

Irritation and Allergy

Insulin injections can cause redness, swelling, or itching in the area where you inject. If the irritation doesn’t go away, talk with your doctor. You may be injecting the insulin incorrectly.

Although less common, some people may be allergic to insulin. This can lead to a rash that covers your entire body, trouble breathing, decreased blood pressure, racing pulse, or sweating. In certain cases, an allergy to insulin can be life-threatening. If you notice any of these symptoms, get immediate medical care.

Diabetic Ketoacidosis

This serious condition can occur if you take insulin, but aren’t getting enough. Without enough insulin, your body isn’t getting the glucose it needs, so it burns fat for energy. This produces acids called ketones, which can build up in your blood and urine and be toxic to your body.

Ketoacidosis can lead to diabetic coma or even death. If you notice any symptoms—such as vomiting, abdominal pain, rapid breathing, or fruity-smelling breath—notify 911 or have someone bring you to the emergency room for treatment.

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Medical Reviewer: William C. Lloyd III, MD, FACS
Last Review Date: 2019 Jun 26

  1. Fowler MJ. Hypoglycemia. Clinical Diabetes.Oct;26(4):170-173. 

  2. Should I Switch Insulin to Lose Weight? Diabetes Forecast, American Diabetes Association. http://www.diabetesforecast.org/2008/nov/should-i-switch-insulin-to-lose-weight.html 

  3. Information for the Physician: HUMLIN R Regular. U.S. Food and Drug Administration. http://www.accessdata.fda.gov/drugsatfda_docs/label/2011/018780s124lbl.pdf 

  4. Ketoacidosis (DKA). American Diabetes Association. http://www.diabetes.org/living-with-diabetes/complications/ketoacidosis-dka.html 

  5. Hypoglycemia (Low Blood Glucose). American Diabetes Association. http://www.diabetes.org/living-with-diabetes/treatment-and-care/blood-glucose-control/hypoglycemia-l... 

  6. Richardson T, Kerr D. Skin-related Complications of Insulin Therapy: Epidemiology and Emerging Management Strategies. Am J Clin Dermatol. 2003;4(10):661-7.

  7. Low Potassium Level. MedlinePlus, U.S. National Library of Medicine. https://medlineplus.gov/ency/article/000479.htm

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