The Facts About Insulin for Diabetes

Has your doctor told you that you need to take insulin? You'll want to get familiar with what it is and how you use it.

Insulin is a hormone that controls blood sugar. There are many types of insulin used to treat diabetes. They include:

  • Rapid-acting insulin. This starts to work within a few minutes and lasts for a couple of hours.
  • Regular- or short-acting insulin. It takes about 30 minutes to work fully and lasts for 3 to 6 hours.
  • Intermediate-acting insulin. This takes 2 to 4 hours to work fully. Its effects can last for up to 18 hours.
  • Long-acting insulin. It can work for an entire day.

Your doctor may prescribe more than one type.

You might need to take insulin more than once daily, to space your doses throughout the day, and possibly to also take other medicines. Your doctor will tell you exactly what you need.

How Do I Take It?

There are several methods. You can give yourself an insulin injection using a needle and syringe, a cartridge system, or pre-filled pen systems. Inhaled insulin, insulin pumps, and a quick-acting insulin device are also available.

If you use an injectable insulin, the place on the body where you give yourself the shot may matter. 

You'll absorb insulin the most consistently when you inject it into your belly. The next best places to inject it are your arms, thighs, and buttocks.

Make it a habit to inject insulin at the same general area of your body, but vary the exact injection spot. This helps minimize scarring under the skin.

What Are the Side Effects?

The major ones include:

  • Low blood sugar
  • Weight gain when you first start using insulin
  • Lumps or scars where you've had too many insulin injections
  • Rash at the site of injection or over the entire body (rare)
  • With inhaled insulin, there's a chance that the lungs could tighten suddenly in people who have asthma or the lung disease COPD.

How Should I Store My Insulin?

If you use injectable insulin, always keep two bottles of each type of your insulin on hand. You can store the bottle that you are using at room temperature (not higher than 80 F) for 30 days. Keep it where it will not get too hot or too cold, and out of direct sunlight.


A good rule of thumb is that if the temperature is comfortable for you, the insulin is safe. You don't need to refrigerate vials of insulin that you are using. But keep extra bottles of insulin in a refrigerator. The night before you are ready to use your new bottle, take it out of the refrigerator and let it warm to room temperature. Don't let your insulin freeze.

For insulin pens, check the package insert for storage instructions.

Always check your insulin bottle. Rapid-acting, short-acting, and certain long-acting types should be clear. Other forms of injectable insulin should look cloudy but not have clumps. 

If you carry a bottle of it with you, be careful not to shake it. That creates air bubbles, which can affect the amount of insulin you withdraw for an injection.

If you use inhaled insulin, store it as directed on the package. You must refrigerate the sealed packages until you're ready to start using them. If you don't refrigerate them, you must use them within 10 days. You can refrigerate packages you've opened, but before you use it, the cartridges should be at room temperature for 10 minutes.

When Do I Take It?

Follow your doctor's advice. The length of time between your insulin shot and meals may vary depending on the type of insulin you use. For example, if you use a rapid-acting type, you would likely take it 10 minutes before eating a meal, or take it with your meal.

If you use regular- or intermediate-acting insulin, you should generally take it about a half-hour before your meals, or at bedtime. If you take your insulin one half-hour before meals, you will absorb your food at the same time that the insulin starts to work. This will help you avoid low blood sugar reactions.

WebMD Medical Reference Reviewed by Michael Dansinger, MD on May 14, 2015



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