Long-Acting Insulin: How It Works
Content created by Healthline and sponsored by our partners. For more details click here.
Content sponsored by our partners. More details »

This content is created by the Healthline editorial team and is funded by a third party sponsor. The content is objective, medically accurate, and adheres to Healthline's editorial standards and policies. The content is not directed, edited, approved, or otherwise influenced by the advertisers represented on this page, with exception of the potential recommendation of the broad topic area.

Read more about Healthline's advertising and sponsorship policy.

Long-Acting Insulin: How It Works

What is insulin?


  1. Long-acting insulin is typically injected once a day.
  2. One possible side effect of long-acting insulin is low blood sugar.
  3. If you change brands of long-acting insulin, you may need a different dose.

When you eat, your pancreas releases a hormone called insulin. Insulin moves sugar (glucose) from your blood to your cells for energy or storage. If you take insulin, you may need some at mealtime to help lower your blood sugar after you eat. But even between meals, you need insulin in small amounts to help keep blood sugar stable.

This is where long-acting insulin comes in.

If you have diabetes, either your pancreas can’t produce enough (or any) insulin, or your cells can’t use it efficiently. To control your blood sugar, you need to replace or supplement the normal function of your pancreas with regular insulin injections.

Types of insulin

Insulin comes in many types. Each type differs in three ways:

  • onset: how quickly it starts working to lower your blood sugar
  • peak: when its effects on your blood sugar are strongest
  • duration: how long it lowers your blood sugar

According to the U.S. Food and Drug Administration (FDA), the five types of insulin are:

  • Rapid-acting insulin: This type starts to work just 15 minutes after you take it. It peaks within 30 to 90 minutes, and its effects last for three to five hours.
  • Short-acting insulin: This type takes about 30 to 60 minutes to become active in your bloodstream. It peaks in two to four hours, and its effects can last for five to eight hours. It is sometimes called regular-acting insulin.
  • Intermediate-acting insulin: The intermediate type takes one to three hours to start working. It peaks in eight hours and works for 12 to 16 hours.
  • Long-acting insulin: This type takes the longest amount of time to start working. The insulin can take up to 4 hours to get into your bloodstream.
  • Pre-mixed: This is a combination of two different types of insulin: one that controls blood sugar at meals and another that controls blood sugar between meals.

Long-acting insulin

Long-acting insulins don’t peak like short-acting insulins — they can control blood sugar for an entire day. This is similar to the action of insulin normally produced by your pancreas to help control blood sugar levels between meals.

Long-acting insulins are also called basal or background insulins. They keep working in the background to keep your blood sugar under control throughout your daily routine.

There are currently four different long-acting insulin products available:

  • insulin glargine (Lantus), lasts up to 24 hours
  • insulin detemir (Levemir), lasts 18 to 23 hours
  • insulin glargine injection (Toujeo), lasts more than 24 hours
  • insulin degludec injection (Tresiba), lasts up to 42 hours

Even though Lantus and Toujeo are both insulin glargine products made by the same manufacturer, the dosing may need to be slightly different. This is because they have different formula concentrations which causes slight changes in the way they control blood sugar. Because of these differences they can't be substituted for each other; each one must be specifically prescribed.

Tresiba is the newest product on the market, and was approved by the FDA on September 25, 2015.

Basaglar (insulin glargine injection) was approved by the FDA on December 16, 2015, but is not yet available.

How to take long-acting insulin

Usually, you inject long-acting insulin once a day to keep your blood sugar levels steady. You use a needle or pen device to give yourself the injection. Be sure to inject your long-acting insulin at the same time every day to avoid lags in insulin coverage or “stacking” your insulin doses. Stacking means taking your doses too close together, causing their activity to overlap.

Your doctor might recommend adding short-acting insulin before a meal to prevent a blood sugar spike after you eat.

If you change brands of long-acting insulin, you may need a different dose. Talk to your doctor for advice if you change brands of any insulin.

Side effects of long-acting insulin

As with any medicine you take, insulin injections can cause side effects.

One possible side effect is low blood sugar (hypoglycemia). Symptoms of low blood sugar include:

  • dizziness
  • chills
  • blurred vision
  • weakness
  • headache
  • fainting

Other possible side effects of insulin injections include pain, redness, or swelling of the skin at the injection site.

Sometimes insulin is given in combination with thiazolidinediones. This drug group includes oral diabetic drugs like Actos and Avandia. Taking insulin with thiazolidinediones increases the risk of fluid retention and heart failure.

For those taking degludec, precautions may be necessary because of its long effect in the body. You doctor may need to increase your dose at a very gradual rate, at least three to four days apart. It will also take longer to clear the drug from your body.

Finding the right insulin for you

No matter which type of insulin you take, it should work well to control your blood sugar. Work with your doctor to find the best type of insulin, and to set a dosing schedule that’s effective and convenient for you.