Insulin is an essential hormone. It helps your body turn food into energy and controls your blood sugar levels. If you have diabetes, your body can’t make enough insulin or can’t use it properly. Your provider can prescribe human-made insulin that you take through an injection (shot), injectable pen or pump. You can also inhale insulin powder.

What is insulin?

Insulin is a naturally occurring hormone made by your pancreas that helps your body use sugar for energy. If your pancreas doesn’t work as it should, it may not make or release the insulin you need to control your blood sugars, resulting in diabetes.

Diabetes is a condition in which your body doesn’t make enough insulin or your body doesn’t use insulin correctly.


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What does insulin do?

Insulin moves glucose from your blood into cells all over your body. Glucose comes from both food and your body’s own natural release of stored glucose. 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 (hyperglycemia).

Many conditions can affect your body’s ability to produce and release insulin. They include:

  • Gestational diabetes, which is diabetes that begins during pregnancy.
  • Prediabetes, when your body is resistant to insulin (can’t use insulin as it should), but blood sugar levels aren’t high enough for a Type 2 diabetes diagnosis.
  • Type 1 diabetes, when your pancreas doesn’t make insulin or doesn’t make enough to control blood sugar.
  • Type 2 diabetes, when your pancreas doesn’t produce enough insulin, or your body can’t use the insulin as it should.
  • Metabolic syndrome (insulin resistance syndrome), a group of risk factors (including insulin resistance) that increase the risk of diabetes and heart disease. Insulin resistance means that the cells in your body can’t use glucose from your blood as energy.

How do you take insulin?

Your healthcare provider may prescribe insulin to lower your blood glucose and keep you healthy. We refer to the insulin available now as human insulin because it's made to act just like the insulin that’s naturally produced.

You can take insulin in a variety of ways based on your needs and lifestyle. Your healthcare team will work with you to determine which is best for you. You may:

  • Give yourself a shot using an insulin pen or a vial and syringe.
  • Receive doses through an insulin pump. The pump attaches to your body with a small catheter under your skin and delivers the insulin.

What are the different types of injectable human insulin?

Most types of insulin are injectable, either through a needle, pen or pump. There are many different types of injectable insulin. Your provider will work with you to prescribe the right type for you and adjust the dosage if your needs change. They will give you detailed instructions for giving yourself an insulin injection. A diabetes educator can help teach you how to take your insulin and guide you through the process.

Some types of insulin start to work quickly and wear off after a few hours. Providers call these types bolus or mealtime insulin because you may take them before a meal. Other types take longer to reach your bloodstream and work for as long as a day or two. Providers call these types basal or background insulin. Your provider may also prescribe a combination of basal and bolus called premixed insulin.

The main types are:

  • 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 and you should take it before meals.
  • Regular insulin (or short-acting insulin): These kinds of insulin include 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 does not peak). It can last up to two days. Types include insulin degludec.

What are the side effects of human insulin?

Some possible side effects of insulin include:

  • Lumps, pits, swelling, redness or itching at the injection site.
  • Hypoglycemia (low blood sugar).
  • Weight gain.

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 isn’t able to make enough insulin, your provider can prescribe human-made insulin as a diabetes treatment. Follow your provider’s instructions carefully when giving yourself insulin. Call your provider or seek medical help right away if you have serious side effects from insulin. To stay healthy and lower your risk of insulin-related health problems, eat right, maintain a healthy weight and exercise regularly.

Medically Reviewed

Last reviewed by a Cleveland Clinic medical professional on 03/07/2022.

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