Diabetes: Rapid-acting Insulin

What is diabetes?

Your body changes most of the food you eat into glucose (a form of sugar). Insulin is a hormone produced by the pancreas that allows glucose to enter all the cells of your body and be used as energy.

Diabetes is a disease that occurs when a person’s body doesn’t make enough insulin or can’t use insulin properly. When you have diabetes, the sugar builds up in your blood instead of moving into the cells. Too much sugar in the blood can lead to serious health problems, including heart disease and damage to the nerves and kidneys.

There are 2 types of diabetes. Type 1 diabetes occurs when the body doesn’t produce any insulin. In type 2 diabetes, the body either doesn’t produce enough insulin or the cells ignore the insulin. Nearly 95% of people who are diagnosed with diabetes have type 2 diabetes.

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 2 to 5 hours. There are 3 types of rapid-acting insulin:

  • Insulin lispro (brand name: Humalog)
  • Insulin aspart (brand name: Novolog)
  • Insulin glulisine (brand name: Apidra)

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

When do I take rapid-acting insulin?

Rapid-acting insulin should be injected 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 rapid-acting insulin?

You may take insulin using a syringe that you fill from a vial or using a dosing pen that contains the insulin. To prepare a dose of rapid-acting insulin using a syringe, follow these steps:

Pull back on the plunger to draw the insulin into the syringe.


  1. Wash your hands.
  2. Take the plastic cover off the new insulin bottle and wipe the top of the bottle with a cotton swab that you have dipped in alcohol. It's best for the insulin to be at room temperature before you inject it.
  3. 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.
  4. 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 (PICTURE 1). The dose of insulin is measured in units.
  5. 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.

If your rapid-acting insulin comes in a pen, your doctor or his or her office staff can show you how to use it correctly. Follow the directions carefully.

Where do I inject the insulin?

Clean the injection area using cotton and alcohol (top). Pinch an area of skin (bottom).

PICTURE 2 Insulin is injected just under the skin. Your doctor or his or her office staff will show you how and where to give an insulin injection. First, clean your skin with cotton dipped in alcohol (PICTURE 2, top). Most people are able to grab a fold of skin and inject insulin at a 90-degree angle (PICTURE 2, bottom; PICTURE 3). If you're thin, you may need to pinch the skin and inject the insulin at a 45-degree angle (PICTURE 4). When the needle is in your skin, you don't need to draw back the syringe plunger to check for blood.

Inject the insulin with the needle at an angle of about 90 degrees.

PICTURE 3 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.

Thin people may find it easier to inject at an angle of 45 degrees.

PICTURE 4 To keep your skin from thickening, try not to inject the insulin in the same place over and over. Instead, rotate injection places.

What is an insulin reaction?

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 the name for 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, if you don't eat enough, 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

How can I deal with an insulin reaction?

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:

  • Nondiet 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 must be mixed together and then injected. 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.

How can I keep my blood sugar level from getting too high or too low?

You need to check your blood sugar level regularly using a blood glucose monitor. Your doctor or his or her 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. He or she 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.
Illustrations by Kathryn Born.

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Written by familydoctor.org editorial staff.

American Academy of Family Physicians

Reviewed/Updated: 05/09
Created: 09/00