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Everything You Need to Know About Insulin

The importance of insulin

Insulin is a hormone made in your pancreas, a gland located behind your stomach. It allows your body to use glucose for energy. Glucose is a type of sugar found in many carbohydrates. After a meal or snack, the digestive tract breaks down carbohydrates and changes them into glucose. Glucose is then absorbed into your bloodstream through the lining in your small intestine. Once glucose is in your bloodstream, insulin causes cells throughout your body to absorb the sugar and use it for energy.

Insulin also helps balance your blood glucose levels. When there’s too much glucose in your bloodstream, insulin signals your body to store the excess in your liver. The stored glucose isn’t released until your blood glucose levels decrease, such as between meals or when your body is stressed or needs an extra boost of energy.

Understanding diabetes

Diabetes occurs when your body doesn't use insulin properly or doesn't make enough insulin. There are two main types of diabetes: type 1 and type 2.

Type 1 diabetes is a type of autoimmune disease. These are diseases in which the body attacks itself. If you have type 1 diabetes, your body can’t make insulin. This is because your immune system has destroyed all of the insulin-producing cells in your pancreas. This disease is more commonly diagnosed in young people, although it can develop in adulthood.

In type 2 diabetes, your body has become resistant to the effects of insulin. This means your body needs more insulin to get the same effects. Therefore, your body overproduces insulin to keep blood glucose levels normal. However, after many years of overproduction, the insulin-producing cells in your pancreas burn out. Type 2 diabetes also affects people of any age, but typically develops later in life. 

Insulin as treatment for diabetes

Injections of insulin as a replacement or supplement to your body’s insulin can help treat both types of diabetes. Because people with type 1 diabetes can’t make insulin, they must use insulin to control their blood glucose levels. Many people with type 2 diabetes can manage their blood glucose levels with lifestyle changes and oral medication. However, if these treatments don’t work, they may also need insulin to help control their blood glucose levels.

Types of insulin treatments

All types of insulin produce the same effect. The makeup of different types of insulin affects how fast and how long they work to help mimic the natural increases and decreases of insulin levels throughout the body during the day.

Rapid-acting insulin: This type of insulin begins working approximately 15 minutes after injection. Its effects can last between two and four hours. It's often used before a meal.

Short-acting insulin: You inject this insulin before a meal. It starts working 30 to 60 minutes after you inject it and lasts five to eight hours.

Intermediate-acting insulin: This type of insulin starts working in 30 minutes to an hour after injection, and its effects may last up to eight hours.

Long-acting insulin: This insulin may not start working until about two hours after you inject it. However, it can last up to 24 hours.

Administration and dosage

You can’t take insulin by mouth. You must inject it with a syringe, insulin pen, or insulin pump. The type of insulin injection you use will be based on your personal preference, health needs, and insurance coverage.

Your doctor will show you how to give yourself the injections. You can inject the insulin under the skin in many different parts of your body, such as your thigh, buttocks, upper arm, and abdomen. Don’t inject insulin within two inches of your belly button, though — your body won’t absorb it as well. You should vary the location of injections to prevent the thickening of your skin from constant insulin exposure.

Learn more: How to give a subcutaneous injection »

Insulin use varies by person according to their blood glucose levels and diabetes management goals. Your doctor may instruct you to give yourself insulin 60 minutes before a meal or just before eating. The amount of insulin you'll need on a daily basis depends on factors such as your diet, your level of physical activity, and the severity of your diabetes. Some people only need one insulin shot per day. Others need three or four. Your doctor may also have you use both a rapid-acting insulin and a long-acting insulin.

Insulin reactions

Hypoglycemia, or blood glucose levels that are too low, can sometimes happen when you take insulin. This is called an insulin reaction. If you exercise too much or don't eat enough, your glucose level can drop too low and trigger an insulin reaction. You need to balance the insulin that you give yourself with food or calories. Symptoms of insulin reactions include:

  • tiredness
  • inability to speak
  • sweating
  • confusion
  • loss of consciousness
  • seizures
  • muscle twitching
  • pale skin


To stop the effects of an insulin reaction, carry at least 15 grams of a fast-acting carbohydrate with you at all times. That’s about equal to any of the following:

  • 1/2 cup of non-diet soda
  • 1/2 cup of fruit juice
  • 5 lifesaver candies
  • 2 tablespoons of raisins

Also, ask your doctor about a special pen called a glucagon pen to help resolve an insulin reaction.

Talk to your doctor

Used appropriately, insulin helps keep your blood glucose level within a healthy range. Healthy blood glucose levels help reduce the risk of diabetes complications, such as blindness and the loss of limbs. It's important that you monitor your blood glucose level regularly if you have diabetes. You should also make lifestyle changes to prevent your blood glucose level from getting too high. You can watch this interactive video guide for suggestions. And of course, talk to your doctor about how you can make your treatment with insulin as effective as possible.

Content licensed from:

Written by: Valencia Higuera
Medically reviewed on: Dec 07, 2016: Lindsay Slowiczek, PharmD

This feature is for informational purposes only and should not be used to replace the care and information received from your health care provider. Please consult a health care professional with any health concerns you may have.
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