Diabetes Planned Visit Notebook

28. All About Insulin

Summa Health System developed this fact sheet for patients who need to take insulin to manage their diabetes. Care providers give it to patients during diabetes planned visits, and it is part of the Diabetes Planned Visit Notebook.

All About Insulin

Family Medicine Center of Akron

Copyright © 1997 American Diabetes Association Adapted from the ADA Patient Information

What Is Insulin?

Inside the pancreas, beta cells make the protein insulin. With each meal, beta cells release insulin to help the body use or store the glucose it gets from food.

People with insulin-dependent (type 1) diabetes no longer make insulin. They need insulin shots to use glucose from meals.

People with non-insulin-dependent (type 2) diabetes make insulin, but their bodies don't respond well to it. Some people with type 2 diabetes need diabetes pills or extra insulin in shots to help their bodies use their own insulin better.

If you have type 1 or type 2 diabetes and inject insulin, you have many questions about insulin. Insulin cannot be taken as a pill. Because it is a protein, it would be broken down during digestion just like the protein in food. It must be injected into the fat under your skin for insulin to get into your blood.

Insulin comes from either animals or is made in labs by bacteria that have gene instructions to make human insulin. Human insulin does not come from humans.

There are three broad types of insulin, based on:

  1. How soon the insulin starts working (onset).
  2. When it works the hardest (peak time).
  3. How long it lasts in your body (duration).

However, each person responds to insulin in his or her own way. That is why onset, peak time, and duration are given as ranges.

Short-acting (Humulin R, Novolin R, Regular) insulin usually reaches the blood within 30 minutes after injection. It peaks 2 to 4 hours later and stays in the blood for about 4 to 8 hours.

Intermediate-acting (Humulin N, Novolin N, NPH) insulins reach the blood 2 to 6 hours after injection. They peak 4 to 14 hours later and stay in the blood for about 14 to 24 hours.

Long-acting (Lente, Ultralente) insulin takes 6 to 14 hours to start working. It has no peak or a very small peak 14 to 24 hours after injection. It stays in the blood between 20 and 36 hours.

Some types of insulin come mixed together. For example, you can buy Regular and NPH insulins already mixed in one bottle. They make life easier if you need to inject two kinds of insulin at the same time. However, you can't adjust the amount of one insulin without also changing how much you get of the other insulin.


Insulins come dissolved in liquids at different strengths. Most people use U-100 insulin. This means it has 100 units of insulin per millimeter of fluid. Be sure that the syringe you use matches the insulin strength. U-100 insulin needs a U-100 syringe. In Europe and Latin America, U-40 insulin is also used.

If you're outside the United States, be certain to match your insulin strength with the correct size syringe.

Storage and Safety

Insulin makers advise storing insulin in the refrigerator, but using cold insulin can make the shot more painful. You can keep the bottle of insulin you are currently using at room temperature or warm the bottle by gently rolling it between your hands before you fill the syringe.

If you buy more than one bottle of insulin at a time, store the extra bottles in the refrigerator until you start to use them.

Never store insulin at very cold (under 36 degrees Fahrenheit) or very hot (over 86 degrees Fahrenheit) temperatures. Extreme temperatures destroy insulin. Do not put your insulin in the freezer or in direct sunlight.

Before using any insulin, check the expiration date. Insulin may lose potency slightly if the bottle has been used for more than 30 days. Look at the bottle closely to make sure the insulin looks normal. If you use Regular, it should be perfectly clear with no floating pieces or color.

If you use NPH or Lente, it should be cloudy, with no floating pieces or crystals on the bottle. If you find any problems, return the bottle of insulin for an exchange or refund.

Insulin Therapy

With your health care team's help, you can find an insulin therapy routine that will control your blood glucose, help you feel good, and fit your lifestyle.

Conventional insulin therapy means taking the same shots at the same times each day—usually a shot in the morning and a shot in the evening.

For most people, conventional therapy prevents dangerously high or low blood glucose levels. But conventional therapy may leave blood glucose levels too high. These higher glucose levels increase the risk of problems with your eyes, kidneys, and nerves.

For that reason, many doctors now advise intensive insulin therapy. This therapy aims to keep your blood glucose as close to normal as possible. Intensive therapy means either taking three or four shots daily or using an insulin pump.

For good results, you must take a very active role in your diabetes care and test your blood glucose level often. Based on your blood glucose records, you and your health care team will fine-tune your treatment plan.

Intensive therapy takes more work but gives you more choices. You are not tied to certain eating or exercise times. However, because you are keeping your blood glucose levels lower, there is a chance of more low blood glucose reactions.

You may also gain some weight. Because you are matching insulin needs closely to glucose levels, your body is able to use and store more of the calories from glucose instead of losing them in the urine.

Talk with your health care team about whether the greater freedom and chance to avoid diabetes complications are worth the drawbacks of intensive therapy.


It is hard to improve your blood glucose control without testing your blood glucose. Writing down your results and looking over weeks or months of results can help you predict and avoid low or high blood glucose levels.

Tests show how exercise, an exciting event, or a special meal affected your glucose level. By knowing that, you can change your insulin to prevent problems.

Site Rotation

The place on your body where you inject insulin affects blood glucose control. Insulin enters the blood at different speeds when injected at different sites. Insulin shots work fastest when given in the abdomen.

Insulin arrives in the blood a little more slowly from the upper arms and even more slowly from the thighs and buttocks.

Injecting insulin in the same general area (for example, your abdomen) will give you the best results from your insulin. This is because the insulin will reach the blood with about the same speed with each shot. Don't inject in exactly the same place each time but move around the same area.

If you take several shots a day, you may want to choose one site (perhaps the upper arm) for morning shots, another site for lunch shots, and a third site for evening shots.

If you inject near the same place each time, hard lumps or extra fatty deposits may develop. Both of these problems are unsightly and make the insulin action less reliable.


Good blood glucose control is all in the timing. The idea is to time your shots so that insulin goes to work when glucose from your food starts to enter your blood. To do this, you need to know how soon your insulin starts to lower your blood glucose. You can find this out by self-monitoring.

Syringe Reuse

Some doctors believe that you can safely reuse your syringe. However, if you are ill, have open wounds on your hands, or have poor resistance to infection for any reason, you should not risk syringe reuse.

Reusing syringes may help you cut costs, avoid buying large supplies of syringes, and reduce waste. However, talk with your doctor or nurse before you begin reusing. They can help you decide whether reuse would be a wise choice for you.

Syringe Disposal

It is time to dispose of a syringe when the needle is dull or bent or if it has come in contact with anything other than clean skin. Proper syringe disposal is important. Your syringe is medical waste.

If you can do it safely, clip the needles off the syringes. When you remove the needle, no one can use the syringe. It is best to buy a device that clips, catches, and contains the needle. Do not use scissors to clip off needles—the flying needle could hurt someone or become lost.

If you do not destroy your needles, recap them. Place the needle or entire syringe in an opaque (not clear) heavy-duty plastic bottle with a screw cap or a plastic or metal box that closes firmly. Do not use a container that will allow the needle to break through. Make sure your syringe container doesn't get recycled.

Your area may have special rules for getting rid of medical waste like used syringes. Ask your refuse company or city or county waste authority what method meets their rules. When traveling, bring your used syringes home. Pack them in a heavy-duty holder, such as a hard plastic pencil box, for transport.

Questions about Insulin? Please call the Family Medicine Center at (330) 375-3584 or 1-800-460-2332.

Page last reviewed October 2014
Page originally created January 2008
Internet Citation: 28. All About Insulin. Content last reviewed October 2014. Agency for Healthcare Research and Quality, Rockville, MD. http://www.ahrq.gov/professionals/education/curriculum-tools/diabnotebk/diabnotebk28.html