Rapid-Acting Insulin

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

Rapid-acting insulin is a treatment option for people with type 2 diabetes (T2D). It starts working within 15 minutes of injection and lasts for 2 to 4 hours. This can help lower blood sugar during and after mealtime.1

Insulin is not usually the first treatment for people with T2D. But some people with T2D need to take rapid-acting insulin before meals. Rapid-acting insulin is often used with longer-acting insulin. Talk to your doctor about the risks and benefits of any medicine you take.2

How does rapid-acting insulin work?

Insulin is a hormone produced by the pancreas. It helps move glucose (sugar) from blood into other cells in your body. This helps lower blood sugar. At mealtimes, the pancreas releases more insulin to handle higher blood sugar levels.3,4

Some people with T2D do not produce more insulin at mealtimes. This leads to high blood sugar after eating. Reducing blood sugar after eating helps control overall blood sugar.3,4

Rapid-acting insulin imitates the way the body produces its own insulin at mealtimes. It absorbs into cells faster than regular insulin. This is why you can take rapid-acting insulin right before mealtime. Rapid-acting insulin:1

  • Starts working within 15 minutes
  • Peaks around 1 hour
  • Lasts for 2 to 4 hours


Some examples of rapid-acting insulin are:5,6

    • Admelog® (insulin lispro), Humalog® (insulin lispro), and Lyumjev® (insulin lispro)
    • Apidra® (insulin glulisine)
    • Afrezza® (insulin apart), Fiasp® (insulin apart), and Novolog® (insulin aspart)

Rapid-acting insulin is often used with longer-acting insulin. This can help control blood sugar after mealtime and throughout the day. Some forms of insulin combine multiple types in one medicine. Examples of these include:5,6

  • Humalog® Mix 50/50 or 75/25 (intermediate-acting NPH [neutral protamine Hagedorn] insulin and insulin lispro)
  • Novolog® Mix 70/30 (intermediate-acting insulin protamine and insulin aspart)
  • Ryzodeg® Mix 70/30 (long-acting insulin degludec and insulin aspart)

What are the possible side effects?

Side effects can vary depending on the specific insulin you are taking. The most common side effects of rapid-acting insulin are:5,6

  • Low blood sugar (hypoglycemia)
  • Skin thickening or pitting (lipodystrophy)
  • Allergic reactions
  • Itching and rash
  • Reactions at the injection site
  • Low levels of potassium in the blood (hypokalemia)
  • 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:5,6

  • Blurry vision
  • Confusion
  • Dizziness
  • Headache
  • Slurred speech
  • Sweating

Allergic reactions can also be serious. Get immediate medical help if you have an allergic reaction. Symptoms include:5,6

  • Breathing problems
  • Rapid heartbeat
  • Rash over your whole body
  • Sweating

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

Other things to know

Take rapid-acting insulin as your doctor describes. You usually inject it under your skin 5 to 15 minutes before a meal. It may also be infused through a pump under the skin.5,6

Try to have food ready before injecting. Do not delay eating.5,6

Rotate where you inject to reduce the risk of side effects. Good spots to inject include your:5,6

  • Abdomen
  • Thigh
  • Upper arm
  • Buttocks

Check your blood glucose levels regularly. Talk to your doctor about your target level. Knowing these numbers can help you and your doctor see how well rapid-acting insulin is working for you. Your doctor may then adjust your dose over time. Do not change your type or dose of insulin unless your doctor tells you to.2

Before you begin taking rapid-acting insulin, tell your doctor about all your health conditions and any other drugs, vitamins, or supplements you take. This includes over-the-counter drugs. Other drugs you take or medical conditions you have can make rapid-acting insulin less safe. Also tell your doctor if you:7

  • Have allergies
  • Have low blood sugar
  • Have eye, kidney, or liver problems
  • Are pregnant or plan to become pregnant
  • Are breastfeeding

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