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Long-Acting Insulin

Reviewed by: HU Medical Review Board | Last reviewed: August 2023

Long-acting insulin is a treatment option for people with type 2 diabetes (T2D). Like other types of insulin, it helps control blood sugar. Long-acting insulin starts working within 1 hour after injection and lasts for 24 hours.1

Insulin is not usually the first treatment for people with T2D. But some people with T2D must take insulin to manage blood sugar. Long-acting insulin is often the first type of insulin used. It can control blood sugar throughout the day. Talk to your doctor about the risks and benefits of using long-acting insulin.1

How does long-acting insulin work?

Insulin is a hormone produced by the pancreas. It helps move glucose (sugar) from your blood into other cells in your body. When you have T2D, your pancreas may not produce enough insulin. Cells may also not respond well to the insulin it produces. This leads to high blood sugar.1

Injectable insulin is a common treatment for people with T2D. Several types of insulin are available. They vary in how quickly they take effect and how long they act. Long-acting insulin is one type. It modifies insulin to cause a slow and steady release.1

Insulin glargine and insulin detemir are the most common types of long-acting insulin. They:2,3

  • Start working within 1 hour
  • Reach their highest levels in the blood around 3 to 14 hours
  • Stay effective for 24 hours


Some examples of long-acting insulin include:4-8

  • Basaglar® (insulin glargine)
  • Lantus® (insulin glargine)
  • Levemir® (insulin detemir)
  • Rezvoglar™ (insulin glargine-aglr)
  • Semglee® (insulin glargine)

What are the possible side effects?

Side effects can vary depending on the specific insulin you are taking. The most common side effects of long-acting insulin are:4-8

  • Low blood sugar (hypoglycemia)
  • Allergic reactions
  • Injection site reactions, including thickening or pitting of the skin
  • Weight gain

Low blood sugar can be serious and life-threatening. Talk to your doctor if you notice signs of low blood sugar. These include:4-8

  • Blurry vision
  • Confusion
  • Difficulty speaking clearly
  • Dizziness
  • Headache
  • Light-headedness
  • Sweating

Another serious side effect of long-acting insulin is allergic reactions. Get immediate help if you have any of these symptoms of an allergic reaction:4-8

  • Difficulty breathing
  • Rapid heartbeat
  • Rash all over your body
  • Sweating

Insulin glargine can cause dangerously low levels of potassium in your blood (hypokalemia) This type of insulin also carries a risk for heart failure. Talk to your doctor about your risk of these side effects.4,5,7,8

These are not all the possible side effects of long-acting insulin. Talk to your doctor about what to expect when taking long-acting insulin. You also should call your doctor if you have any changes that concern you when taking long-acting insulin.

Other things to know

Take long-acting insulin as your doctor describes. It is usually administered under the skin using an injection pen. Good spots to inject include the:2,3

  • Abdomen
  • Thigh
  • Upper arm
  • Buttocks

Your doctor may adjust your dose over time. Do not change the type or dose of insulin you take unless your doctor tells you to. Check your blood sugar regularly. Talk to your doctor about ideal levels of blood sugar for you. Do not take long-acting insulin if you have low blood sugar.2,3

Before beginning treatment for T2D, tell your doctor about all your health conditions and any other drugs, vitamins, or supplements you take. This includes over-the-counter drugs. Other medical conditions or drugs you take can make long-acting insulin less safe. Be sure to tell your doctor if you:2,3

  • Have allergies
  • Have any liver, kidney, or heart problems
  • Take thiazolidinedione drugs
  • Are pregnant or plan to become pregnant

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