Long-acting insulin helps people with diabetes maintain normal blood sugar levels throughout the day. Unlike short-acting insulin, it never peaks, keeping an even sugar level in your blood.

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.

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 60 minutes, and its effects last for 3 to 5 hours.
  • Short-acting insulin: This type takes about 30 to 60 minutes to become active in your bloodstream. It peaks in 2 to 3 hours, and its effects can last for 3 to 6 hours. It is sometimes called regular-acting insulin.
  • Intermediate-acting insulin: The intermediate type takes 2 to 4 hours to start working. It peaks in 8 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 2 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 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:

Even though Lantus and Toujeo are both insulin glargine products made by the same manufacturer, the dosing may need to be slightly different. That’s because they have different formula concentrations which cause 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.

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 if you change brands of any 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 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 3 to 4 days apart. It will also take longer to clear the drug from your body.

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.