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Insulin Therapy

Last Updated June 2023 | This article was created by familydoctor.org editorial staff and reviewed by Robert "Chuck" Rich, Jr., MD, FAAFP

When you digest food, your body changes most of the food you eat into glucose (a form of sugar). Insulin allows this glucose to enter all the cells of your body and be used as energy. When you have diabetes, your body doesn’t make enough insulin or can’t use it properly. Because of this, the glucose builds up in your blood instead of moving into the cells. Too much glucose in the blood and not enough in your cells can lead to serious health problems.

All people who have type 1 diabetes and some who have type 2 diabetes need to take insulin. It helps control their blood sugar levels. The goal is to keep your blood sugar level in a normal range as much as possible. Insulin is usually taken by injection (a shot). It can also be taken using an insulin pen or an insulin pump.

Path to improved health

How often will I need to take insulin?

You and your doctor will develop a schedule that is right for you. Most people who have diabetes and take insulin need at least 2 insulin shots a day for good blood sugar control. Some people need 3 or 4 shots a day.

Do I need to monitor my blood sugar level?

Yes. Monitoring and controlling your blood sugar is key to preventing the complications of diabetes. If you don’t already monitor your blood sugar level, you will need to learn how. Checking your blood sugar involves pricking your finger to get a small drop of blood that you put on a test strip. You then insert the strip into a machine called a glucose meter. The results will tell you whether your blood sugar is in a healthy range

There are newer devices that can monitor your blood sugar without pricking your finger. Some of these work by wearing a sensor on your arm or abdomen. The sensor will read your glucose levels from fluids just underneath your skin. The information is then transmitted to a reader or an app on your phone.

Your doctor will help you decide which method is best for you.

When should I take insulin?

You and your doctor should discuss when and how you will take your insulin. Each person’s treatment is different. Some people who use regular insulin take it 30 to 60 minutes before a meal. Some people who use rapid-acting insulin take it just before they eat.

Types of insulin:

  • Rapid-acting insulin (such as insulin lispro, insulin aspart, and insulin glulisine) starts working in about 15 minutes. It lasts for 3 to 5 hours.
  • Short-acting insulin (such as regular insulin) starts working in 30 to 60 minutes and lasts 5 to 8 hours.
  • Intermediate-acting insulin (such as insulin NPH) starts working in 1 to 3 hours and lasts 12 to 16 hours.
  • Long-acting insulin (such as insulin glargine and insulin detemir) starts working in about 1 hour and lasts 20 to 26 hours.
  • Premixed insulin is a combination of 2 types of insulin (usually a rapid- or short-acting insulin and an intermediate-acting insulin).

What is rapid-acting insulin? How can it help control my blood sugar level?

Rapid-acting insulin starts working more quickly than other types of insulin. It begins working within 15 minutes and leaves your body after 3 to 5 hours.

To keep your blood sugar level steady throughout the day, your doctor may also prescribe a longer-acting insulin. Or they may prescribe another drug for you to take each day in addition to rapid-acting insulin.

When do I take rapid-acting insulin?

You should inject rapid-acting insulin no more than 15 minutes before you eat. Your doctor will tell you how much insulin to inject. Remember, you should not wait more than 15 minutes to eat after you take this insulin shot.

Rapid-acting insulin can be more convenient to take than regular insulin. With regular insulin, you inject the insulin and then wait 30 to 60 minutes before eating. Many people find it hard to time their meals around regular insulin injections. Sometimes they end up eating too soon or too late. Then they don’t achieve the best blood sugar control. Since rapid-acting insulin is taken so close to mealtime, it may help you control your blood sugar more effectively.

Can I mix rapid-acting insulin with other types of insulin?

You can mix a rapid-acting insulin with an intermediate-acting insulin, according to your doctor’s instructions. Rapid-acting insulin should always be drawn into the syringe first. This will keep the intermediate-acting insulin from getting into the rapid-acting insulin bottle. After mixing rapid-acting insulin in the same syringe with an intermediate-acting insulin, you must inject the mixture under your skin within 15 minutes. Remember to eat within 15 minutes after the injection.

How do I prepare the correct dose of insulin?

You may take insulin using a syringe that you fill from a vial or using a dosing pen that contains the insulin. If your rapid-acting insulin comes in a pen, your doctor or their office staff can show you how to use it correctly. Follow the directions carefully.

  • Wash your hands.
  • Take the plastic cover off the new insulin bottle. Wipe the top of the bottle with a cotton swab that you have dipped in alcohol. It’s best for rapid-acting insulin to be at room temperature before you inject it.
  • Pull back the plunger of the syringe. This draws air into the syringe equal to the dose of insulin that you are taking. Then put the syringe needle through the rubber top of the insulin bottle. Inject air into the bottle by pushing the syringe plunger forward. Then turn the bottle upside down.
  • Make sure that the tip of the needle is in the insulin. Pull back on the syringe plunger to draw the correct dose of insulin into the syringe. The dose of insulin is measured in units.
  • Make sure there are no air bubbles in the syringe before you take the needle out of the insulin bottle. Air bubbles can cut down the amount of insulin that you get in your injection. If air bubbles are present, hold the syringe and the bottle straight up in one hand, tap the syringe with your other hand and let the air bubbles float to the top. Push on the plunger of the syringe to move the air bubbles back into the insulin bottle. Then withdraw the correct insulin dose by pulling back on the plunger.
  • Clean your skin with cotton dipped in alcohol. Grab a fold of skin and inject the insulin at a 90-degree angle. (If you’re thin, you may need to pinch the skin and inject the insulin at a 45-degree angle.) When the needle is in your skin, you don’t need to draw back the syringe plunger to check for blood.

Where do I inject the insulin?

Insulin is injected just under the skin. Your doctor or their office staff will show you how and where to give an insulin injection. The usual places to inject insulin are the upper arm, the front and side parts of the thighs, and the abdomen. Don’t inject insulin closer than 2 inches from your belly button.

To keep your skin from thickening, try not to inject the insulin in the same place over and over. Instead, rotate injection places.

Things to consider

If you’re going to use rapid-acting insulin, you need to be aware of insulin reactions and how to treat them. Rapid-acting insulin begins to work very quickly. So while you and your doctor are working to find the right dosage of this insulin, you may have some insulin reactions.

Hypoglycemia is a condition in which the level of sugar in your blood is too low. If you use insulin, your blood sugar level can get too low if you exercise more than usual or if you don’t eat enough. It also can get too low if you don’t eat on time or if you take too much insulin. Most people who take insulin have insulin reactions at some time. Signs of an insulin reaction and hypoglycemia include the following:

  • Feeling very tired
  • Yawning frequently
  • Being unable to speak or think clearly
  • Losing muscle coordination
  • Sweating
  • Twitching
  • Having a seizure
  • Suddenly feeling like you’re going to pass out
  • Becoming very pale
  • Losing consciousness

People who have diabetes should carry at least 15 grams of a fast-acting carbohydrate with them at all times in case of hypoglycemia or an insulin reaction. The following are examples of quick sources of energy that can relieve the symptoms of an insulin reaction:

  • Non-diet soda: ½ to ¾ cup
  • Fruit juice: ½ cup
  • Fruit: 2 tablespoons of raisins
  • Milk: 1 cup
  • Candy: 5 Lifesavers
  • Glucose tablets: 3 tablets (5 grams each)

If you don’t feel better 15 minutes after having a fast-acting carbohydrate, or if monitoring shows that your blood sugar level is still too low, have another 15 grams of a fast-acting carbohydrate.

Teach your friends, work colleagues, and family members how to treat hypoglycemia, because sometimes you may need their help. Also, keep a supply of glucagon on hand. Glucagon comes in a kit with a powder and a liquid that you must mix and then inject. It will raise your blood sugar level. If you are unconscious, or you can’t eat or drink, another person can give you a shot of glucagon. Talk to your doctor to learn when and how to use glucagon.

You need to check your blood sugar level regularly using a blood glucose monitor. Your doctor or their office staff can teach you how to use the monitor. You’ll need to write down each measurement and show this record to your doctor. They will use this information to decide how much insulin is right for you.

Blood sugar measurements can vary depending on your lifestyle. Stress levels, how often you exercise, and how fast your body absorbs food can affect measurements. Hormonal changes related to puberty, menstrual cycles, and pregnancy can, too. Illness, traveling, or a change in your routine may mean that you have to monitor your blood sugar level more often.

Questions for your doctor

  • Do I need insulin to control my type of diabetes?
  • What type of insulin should I take?
  • How often do I need to check my blood sugar?
  • How can I know how much insulin to take?
  • What if insulin doesn’t seem to lower my blood sugar?
  • What should I do to keep my insulin from getting too low overnight?


National Institutes of Health, MedlinePlus: Insulin Injection

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