Insulin is an essential hormone. It helps your body turn food into energy and manages your blood sugar levels. If you have diabetes, your body can’t make enough insulin or can’t use it properly. Your healthcare provider can prescribe manufactured insulin that you take through an injection (shot), injectable pen or pump. Inhalable insulin is also an option.


What is insulin?

Insulin is a naturally occurring hormone your pancreas makes that’s essential for allowing your body to use sugar (glucose) for energy. If your pancreas doesn’t make enough insulin or your body doesn’t use insulin properly, it leads to high blood sugar levels (hyperglycemia). This results in diabetes.

There are also manufactured types of insulin that people with diabetes use to manage the condition.

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What does insulin do?

Insulin moves glucose from your blood into cells all over your body. Glucose comes from both the food and drinks you consume and your body’s natural release of stored glucose (glycogen). Glucose is your body’s main — and preferred — source of energy.

All of your body’s cells need energy. Think of insulin as the key that opens the doors of the cells in your body. Once insulin opens your cell doors, glucose can leave your bloodstream and move into your cells where you use it for energy.

Without enough insulin, glucose can’t get into your cells and instead builds up in your blood. This leads to high blood sugar and diabetes. A total lack of insulin for a prolonged time leads to a life-threatening complication called diabetes-related ketoacidosis (DKA).

Does insulin lower or raise blood sugar?

Insulin lowers your blood sugar level. Glucagon (another hormone) naturally raises it. Your body uses these two hormones to balance out your blood sugar level to keep it in a healthy range.

If you have diabetes, too much (manufactured) insulin can lead to low blood sugar (hypoglycemia). In this case, you may need to consume sugar to raise your blood sugar level. There are manufactured forms of glucagon available with a prescription for emergency use to treat severe low blood sugar. Talk to your healthcare provider or diabetes care and education specialist to find out if glucagon should be included in your treatment plan.


Where is insulin produced?

Your pancreas produces insulin. More specifically, beta cells in the islets of Langerhans in the pancreas make the hormone. This is the endocrine function of your pancreas, meaning it releases insulin directly into your bloodstream.

Your pancreas also has an exocrine function — it releases enzymes into certain ducts to help with digestion.


Conditions and Disorders

What conditions involve issues with insulin?

Many conditions can develop when you have a lack of natural insulin or too much.

Diabetes and a lack of insulin

Diabetes results from a lack of functional insulin, which leads to high blood sugar.

Damage to your pancreas causes certain types of diabetes, like:

  • Type 1 diabetes: This is an autoimmune condition in which your immune system attacks the insulin-producing cells in your pancreas. It eventually results in a total lack of natural insulin.
  • Type 3c diabetes (secondary or pancreatogenic diabetes): This condition develops when your pancreas experiences damage that affects its ability to produce insulin. Conditions like chronic pancreatitis and cystic fibrosis can lead to pancreas damage that causes diabetes. Having your pancreas removed (pancreatectomy) also results in Type 3c diabetes.
  • Latent autoimmune diabetes in adults (LADA): Like Type 1 diabetes, LADA also results from an autoimmune reaction, but it develops much more slowly than Type 1. People diagnosed with LADA are usually over the age of 30.

Insulin resistance is the other major cause of diabetes. This happens when cells in your muscles, fat and liver don’t respond as they should to insulin. Insulin resistance can lead to conditions like:

  • Prediabetes: Prediabetes happens when you have elevated blood sugar levels, but they’re not high enough to be considered Type 2 diabetes. Insulin resistance is the main cause.
  • Type 2 diabetes: This condition happens when insulin resistance is too strong for your pancreas to overcome, resulting in high blood sugar.
  • Gestational diabetes: This condition can develop during pregnancy. Researchers believe the placenta releases hormones that cause insulin resistance. If your pancreas can’t overcome this resistance, it leads to gestational diabetes. It typically goes away after you deliver your baby.

There’s also a genetic form of diabetes called maturity-onset diabetes of the young (MODY). MODY, also called monogenic diabetes, happens due to an inherited genetic mutation (change) that affects how your body makes and uses insulin.

Excess insulin

A rare tumor called an insulinoma makes your pancreas produce excess insulin. This causes you to have frequent — and sometimes severe — low blood sugar. Most insulinomas are curable with surgery.


What are the types of insulin for diabetes?

There are many different types of insulin. Most types are injectable, either through a needle, pen or pump. There’s also inhalable insulin. If you have diabetes, your provider will work with you to prescribe the right type(s) for you and adjust the dosage when your needs change.

The main types of insulin based on how fast they work and how long they last include:

  • Rapid-acting insulin: This kind of insulin begins to work within five to 20 minutes and keeps working for three to five hours. It peaks (is most effective) about an hour or two after you inject it. Types of rapid-acting insulin include insulin glulisine. Inhaled insulin is also considered rapid-acting. You should take it before meals.
  • Regular insulin (or short-acting insulin): This kind of insulin includes Novolin R® and Humulin R®. They begin working about 30 to 45 minutes after injection and wear off after about five to eight hours. Regular insulin peaks about two to four hours after injection.
  • Intermediate-acting insulin: This type begins working in about two hours and is most effective between four and 12 hours after injection. It wears off in 14 to 24 hours. Types include isophane insulin (NPH).
  • Long-lasting insulin: It takes about an hour for this type of insulin to reach your bloodstream and start working. It peaks between three and 14 hours after injection. It lasts up to a day. Types include insulin glargine.
  • Ultra long-acting insulin: Reaching the bloodstream in about six hours, this type of insulin has the same level of effectiveness for several hours (it doesn’t peak). It can last up to two days. Types include insulin degludec.


What are the side effects of insulin?

The most common complication of insulin treatment is low blood glucose levels (hypoglycemia) from taking too much insulin for your needs.

Other possible side effects of insulin treatment, which are rare, include:

  • Skin reactions with injected insulin: Injecting insulin in the same area frequently can cause fat deposits to form under your skin, making your skin look lumpy. It can also destroy fat, causing indentation of your skin. This issue is called localized lipodystrophy. It can decrease the absorption of injected insulin, so it’s important to frequently rotate injection sites.
  • Allergic reaction to insulin: Some people can develop allergic reactions to certain types of insulin. It can cause pain and burning, followed by skin discoloration, itchiness and swelling around the injection site for several hours.
  • Developing insulin antibodies: In very rare cases, your body can produce antibodies to manufactured insulin because it’s not exactly like natural insulin. These antibodies may interfere with how well the manufactured insulin works. And it may require you to take very large doses of insulin.

What are the sites of injection for insulin?

You can inject several areas of your body with insulin. In general, the areas where you typically have body fat (adipose tissue) are the best sites. These include:

  • Your belly — at least 2 inches (5 centimeters) away from your belly button.
  • The front or side of your thighs.
  • The back of your upper arms.
  • Your upper buttocks.

It’s important to mix up where you inject insulin to prevent skin complications.

Additional Common Questions

What are normal insulin levels?

“Normal” doesn’t really exist for insulin levels because each person is different, and your insulin needs vary widely from hour to hour every day. Several factors impact your insulin levels, like:

  • The type and amount of food (mainly carbohydrate-containing food) you eat.
  • When and how often you eat.
  • Your activity level and what type of activity you’re doing (like cardio or weightlifting).
  • If you’re sick or stressed.
  • If you’re awake or asleep.
  • Other hormones.
  • Certain medications, like corticosteroids.

In addition, there’s no common test to check your insulin levels specifically.

Do people with Type 2 diabetes need insulin?

Some people — but not all — with Type 2 diabetes need insulin to best manage the condition.

There are several other types of medications for Type 2 diabetes, like oral medications and GLP-1 agonist injections. These medications combat insulin resistance in different ways. If insulin resistance is severe, these medications may not be enough to maintain healthy blood sugar levels. This is when you’d need insulin.

How long can a person with diabetes go without insulin?

A person with insulin-dependent diabetes needs manufactured insulin to live. Without it, DKA, a life-threatening complication, can develop.

DKA is an acute complication, which means it has a severe and sudden onset. It can develop within 24 hours. If you’re vomiting, it could develop much more quickly. It’s essential to call your healthcare provider or go to the hospital as soon as you experience symptoms to get treatment before DKA becomes more severe. Without treatment, DKA is fatal.

A note from Cleveland Clinic

Insulin is an essential hormone that helps you stay healthy and keeps your body working like it should. If your body can’t make enough insulin or use it properly, your healthcare provider can prescribe manufactured insulin as a diabetes treatment. Follow your provider’s instructions carefully when giving yourself insulin. And be sure to seek medical help right away if you have signs of DKA or experience severe low blood sugar.

Medically Reviewed

Last reviewed on 01/17/2024.

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