Insulin vs. Blood Sugar: Understanding How to Manage Diabetes

Understanding the role of insulin and glucose (blood sugar) in the body is important part of managing type 2 diabetes. Insulin is a hormone that lowers blood sugar, preventing excess glucose from damaging cells. In type 2 diabetes, blood sugar is high due to having cells that do not take up enough sugar because they are resistant to insulin.

This article explains the role of insulin and its impact on blood sugar, and what happens when this process is dysfunctional.

Couple with diabetes learns to use blood sugar monitor

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What Is Insulin?

Insulin is a hormone made by the pancreas. Increased levels of blood sugar, such as what occurs after a meal, signal the pancreas to release insulin in the bloodstream. Insulin tells cells throughout the body to take up blood sugar, which is either used then for energy or stored as glycogen or fat for later use.

Insulin was discovered in the early 1920s and over the next decades, developed into a lifesaving pharmaceutical product for people with diabetes.

What Is Blood Sugar?

Blood sugar, also known as blood glucose, is the concentration of sugar in the blood, typically given in units of milligrams per deciliter (mg/dL). The normal fasting blood sugar level is less than 100 mg/dL. However, in diabetes, this level is above 126 mg/dL. Numbers in between are considered in the prediabetes range.

The body needs to maintain blood sugar within a specific range. When glucose is too low, hypoglycemia can occur. In hypoglycemia, the brain doesn't have enough energy, which can lead to coma and death unless treated.

High levels of sugar can be a problem in both the short term and long term. In the short term, high levels of blood sugar in type 2 diabetes can lead to a dangerous state called hyperglycemic hyperosmolar state (HHS), which is marked by severe dehydration and can be life-threatening. In the long term, high blood sugar damages tissues and organs throughout the body.

Insulin Resistance and Diabetes

Type 2 diabetes is most often caused by insulin resistance, a situation in which cells don't respond appropriately to insulin. Higher and higher levels of insulin are required to stimulate cells to take up blood sugar. Eventually, the pancreas can't keep up with the amount of insulin needed, resulting in high blood sugar levels.

Treating High Blood Sugar With Insulin

Most available forms of insulin are injectable, delivered via needle, pen, or a pump. There is also an inhaled form of insulin called Afrezza.

Types of Insulin

There are several different types of exogenous insulin (insulin not made in the body itself, but that's injected, pumped, or inhaled). They are different in how quickly they are absorbed, when they reach their peak effect, and how long they last in the body.

Usually insulin is prescribed as a regimen that includes a basal dose of intermediate or long-acting insulin with bolus dosing (a single dose given in a short period of time) of rapid-acting insulin given before meals.

Types of Insulin
 Type of Insulin  Initial Effect Peak Effect   Duration  Examples
 Rapid-acting  15 minutes  1–2 hours  2–4 hours NovoLog (insulin aspart), Humalog (insulin lispro)
 Short-acting  30 minutes  2–3 hours  3–6 hours Humulin R, Novolin R, and U-500 (human regular insulin)
Intermediate-acting   2–4 hours  4–12 hours  12–18 hours Humulin N and Novolin N (NPH)
Long-acting   2–4 hours  n/a  24 hours Levemir (detemir), Lantus (glargine)
Ultra long-acting   6 hours  n/a  36+ hours  Toujeo (glargine U-300), Tresiba (insulin degludec)

Side Effects of Insulin

Side effects of insulin can result from the delivery of insulin, the effect of insulin on the body, and a possible allergy to the ingredients in the medication.

Side effects may include:

  • Redness or irritation at injection site
  • Scar tissue or skin thickening at injection site (lipohypertrophy)
  • Swelling at the injection site
  • Weight gain

Effects of Insulin on Body

In the short term, insulin can cause seriously low blood sugar, or hypoglycemia. Symptoms can include:

  • Light-headedness or dizziness
  • Shaking or tremors
  • Sweating and clamminess
  • Blurry vision
  • Pale skin
  • Rapid heart rate
  • Confusion
  • Loss of consciousness
  • Seizure

Symptoms of hypoglycemia need prompt treatment. If you have symptoms of low blood sugar, check your blood sugar if you are able and immediately ingest some carbohydrates by drinking juice or eating crackers.

Possible allergies to the other components in the drug can also cause serious allergic reaction known as anaphylaxis:

  • Facial swelling
  • Difficulty breathing
  • Fast heart rate
  • Dizziness
  • Loss of consciousness


Seek immediate medical attention if you have symptoms of an allergic reaction to insulin as this can be life-threatening


Before the discovery and development of insulin as a medication, diabetes had a much worse prognosis. With better understanding of the condition and with available treatment options, diabetes is a treatable chronic disease.

Studies demonstrate that people with diabetes have decreased life expectancy compared to those without diabetes. This is particularly true in those with poorly controlled blood sugar, kidney disease, and a younger age at diagnosis.

It's especially important for people with diabetes to stop smoking and to control other health conditions like high blood pressure and high cholesterol to lower their risk of cardiovascular disease, which is a major cause of death in people with diabetes.


Chronically high levels of blood sugar are damaging to tissues and organs in the body, which may lead to the following complications:


Insulin and blood sugar are both vital to the body. While blood sugar is an essential form of energy for the body, levels that are too high or too low are life-threatening. Insulin helps keep blood sugar in check. In people with type 2 diabetes, the relationship between insulin and blood sugar is dysfunctional, resulting in high blood sugar.

A Word From Verywell

A diagnosis of type 2 diabetes can be daunting, particularly when treatment with insulin is needed. Learning how insulin works and how to administer it and keep your blood sugar levels in a safe range can take a lot of work and practice. Know that your healthcare team is available to answer questions and help get you on track to better blood sugar control and better health.

Frequently Asked Questions

  • Does insulin reduce or increase blood sugar?

    Insulin lowers blood sugar. Insulin is a hormone made in the pancreas that is secreted into the bloodstream after a meal. It helps cells in the body take up glucose so it can be used as energy or stored for later use.

  • At what blood sugar level do you need to take insulin?

    Insulin is often required to treat high blood sugar in those with type 2 diabetes. Insulin should be considered in newly diagnosed type 2 diabetic patients with hemoglobin A1c greater or equal to 10% or blood sugar greater than or equal to 300mg/dL, and in those whose blood sugar remains uncontrolled after three months on a multi-drug regimen.

  • Can you lower blood sugar without insulin?

    While insulin is an essential hormone, not everyone with type 2 diabetes needs to be on insulin. A combination of exercise, dietary change, weight loss, and oral medications can avert the need for exogenous insulin (insulin that's not made in the body but needs to come from other sources). For some people with type 2 diabetes, it's possible with diet, exercise, and weight loss to lower blood sugar enough not require any blood sugar lowering medications. This is known as diabetes regression.

18 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Centers for Disease Control and Prevention. What is diabetes?

  2. Kolb H, Kempf K, Röhling M, et al. Insulin: too much of a good thing is badBMC Med. 2020;18(224). doi:10.1186/s12916-020-01688-6

  3. Food and Drug Administration. 100 years of insulin.

  4. American Diabetes Association. Diagnosis.

  5. American Diabetes Association. Hypoglycemia.

  6. MedlinePlus. Diabetic hyperglycemic hyperosmolar syndrome.

  7. National Institute of Diabetes and Digestive and Kidney Diseases. Insulin resistance and prediabetes.

  8. MedlinePlus. Diabetes- insulin therapy.

  9. American Diabetes Association. Insulin basics.

  10. American Diabetes Association. Insulin basics.

  11. MedlinePlus. Human insulin injection.

  12. American Academy of Allergy, Asthma & Immunology. Anaphylaxis.

  13. Preston SH, Choi D, Elo IT, Stokes A. Effect of diabetes on life expectancy in the United States by race and ethnicityBiodemography Soc Biol. 2018;64(2):139-151. doi:10.1080/19485565.2018.1542291

  14. Tancredi M, Rosengren A, Svensson AM, et al. Excess mortality among persons with type 2 diabetesN Engl J Med. 2015;373(18):1720-1732. doi:10.1056/NEJMoa1504347

  15. National Institute of Diabetes and Digestive and Kidney Diseases. What is diabetes?

  16. American Diabetes Association. 8. Pharmacologic Approaches to Glycemic Treatment: Standards of Medical Care in Diabetes—2023Diabetes Care. 2023;46(Suppl 1):S140-S157. doi:10.2337/dc23-S009

  17. National Institute of Diabetes and Digestive and Kidney Disorders. Insulin, medicines, and other diabetes treatments.

  18. Perreault L, Pan Q, Mather KJ, Watson KE, Hamman RF, Kahn SE. Effect of regression from prediabetes to normal glucose regulation on long-term reduction in diabetes risk: results from the diabetes prevention program outcomes studyThe Lancet. 2012;379(9833):2243-2251. doi:10.1016/S0140-6736(12)60525-X

By Angela Ryan Lee, MD
Angela Ryan Lee, MD, is board-certified in cardiovascular diseases and internal medicine. She is a fellow of the American College of Cardiology and holds board certifications from the American Society of Nuclear Cardiology and the National Board of Echocardiography. She completed undergraduate studies at the University of Virginia with a B.S. in Biology, medical school at Jefferson Medical College, and internal medicine residency and cardiovascular diseases fellowship at the George Washington University Hospital. Her professional interests include preventive cardiology, medical journalism, and health policy.