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How fast does insulin lispro work?

Medically reviewed by Carmen Pope, BPharm. Last updated on June 16, 2023.

Official answer

  • Lispro starts working within 0 to 15 minutes of administration
  • Lispro can be given 15 minutes before a meal or with a meal.
  • Lispro is more convenient and safer than regular insulin.

Lispro is an analog insulin that is made by genetically modifying the structure of human insulin to give it a faster onset of effect and a shorter duration of action. Lispro:

  • Starts working within 0 to 15 minutes after administration
  • Peaks in 30 to 90 minutes
  • Keeps working for less than five hours (usually two to four hours).

This means it can be administered 15 minutes before or with a meal. This has safety benefits over regular insulin that needs to be administered 30 minutes before food, especially if a meal is delayed or forgotten because hypoglycemia may result.

Lispro also has a shorter duration of effect than regular insulin. This allows it to better mimic how insulin is naturally released in people without diabetes and reduces the risk of side effects such as low blood sugar levels (hypoglycemia) following a meal.

How is lispro made?

Insulin lispro is an analog insulin; another name for this is a genetically modified insulin. Human insulin is made up of a linked A and B polypeptide chains and insulin lispro is made by switching the sequence of two beta-chain amino acids: the proline at B-28 is switched with the lysine at B-29.

This results in more rapid dissolution of the insulin to a dimer and then to a monomer which means it is absorbed more rapidly after subcutaneous injection and lasts for less than five hours.

Although one unit of insulin lispro has the same glucose-lowering effect as one unit of regular insulin, it has:

  • Faster subcutaneous absorption
  • An earlier and greater insulin peak
  • More rapid post-peak decreases.

A longer-acting form of insulin lispro is also available called insulin lispro protamine suspension.

Humalog 75:25 contains insulin lispro protamine suspension as the intermediate-acting insulin and insulin lispro as the short-acting insulin.

What is insulin?

Insulin is a hormone that is produced naturally in our bodies. Its main role is to allow cells throughout the body to uptake glucose (sugar) and convert it into a form that can be used by these cells for energy. Without insulin, we cannot survive, and death from diabetes was a common occurrence until insulin was discovered in the early 1900s by Frederick Banting and Charles Best.


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