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How Long Does Insulin Last After Injection?

What is insulin therapy?

Insulin comes in many different formulations that may be short- or long-acting, prescribed depending on the person's diabetes condition.Insulin comes in many different formulations that may be short- or long-acting, prescribed depending on the person's diabetes condition.

Insulin therapy is a treatment for keeping the blood sugar levels within the normal range. Insulin therapy is the mainstay treatment for managing type I diabetes and poorly controlled type II diabetes mellitus.

Insulin is a natural hormone produced by the pancreas, which regulates blood sugar levels. Insulin therapy is administered when the body produces insufficient insulin or uses it inefficiently.

Insulin was discovered about 80 years ago, and initially animal insulin was used in treatment. Much better formulations which closely mimic human insulin are now available. The newer products are flexible in dosage and use, with more efficacy and far fewer allergic reactions.

What does insulin do?

Insulin maintains a normal range of blood sugar levels by sending signals to the fat and muscle cells to absorb the glucose from the blood, which these cells then convert into energy. Insulin also signals the liver to convert the extra glucose in the blood into glycogen to store for future use.

How long does insulin last after injection?

The duration of insulin effects depends on the type of insulin used. There are five types of insulin:

  • Rapid-acting insulin: Onset is within 15 minutes and duration of effects last up to five hours.
  • Short-acting insulin: Onset is in 30-60 minutes and duration of effects last up to 10 hours.
  • Intermediate-acting insulin: Onset of two to four hours with duration of effects lasting 12-18 hours.
  • Long-acting insulin: Onset of three to four hours with duration of effects lasting over 24 hours.
  • Combination insulin: Mixture of rapid-acting and long-acting insulins, which has quick onset and long-lasting effect.

A protein obtained from fish, known as neutral protamine Hagedorn (NPH), is added to insulin to slow down its absorption and make the effects last longer. NPH also makes the insulin solution appear cloudy to the eye.

The long-lasting insulins are known as basal insulins and provide a constant, steady supply to bring down high resting blood sugar levels. Short-acting insulins are known as bolus insulins. They act fast to bring down blood sugar spikes that come with meals.

What is the purpose of insulin shots?

Uncontrolled high sugar levels (hyperglycemia) in the blood can lead to several diseases affecting multiple organs in the body. Insulin shots bring down the blood sugar level by taking over the functions of the natural insulin in people who have impaired insulin production or function.

Insulin shots are used to treat hyperglycemia in people who have:

  • Type I diabetes: Also known as juvenile diabetes, a condition in which the insulin producing capacity of pancreas is destroyed by the immune system due to a genetic predisposition, disease or injury to the pancreas
  • Type II diabetes: Adult onset disease in which the pancreas does not produce sufficient insulin or the body does not absorb insulin well, and blood sugar level is not controlled by oral therapy.

Bolus insulins are usually injected before a meal to control the sugar level spike in diabetic patients who experience high blood sugar after a meal. Type I diabetic patients starting on insulin therapy and Type II diabetic patients transitioning from oral medication to insulin therapy usually start with basal insulin injections.

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How is insulin injection given?

Insulin injections are usually administered by the patients, themselves, their caregivers or a parent/guardian in the case of a child. Insulin injections are subcutaneous, administered in the fat tissue beneath the skin. The sites for the injection, which should regularly rotate, may be:

  • Front or side of the thigh
  • Abdomen (faster absorption)
  • Outer side of the upper arm
  • Upper outer quadrant of the buttocks

The important points of care for the patients during self-administration of insulin injections include the following:

  • Washing hands before injection
  • Correct time, dose and technique to administer the injection
  • Dealing with possible steep drop in blood sugar (hypoglycemia) with insulin

Injection technique

Insulin injection with syringe

  • Roll the insulin bottle several times between the palms (should not be shaken).
  • Remove the lid and wipe the bottle’s rubber top with an alcohol swab.
  • Pull air into the syringe by pulling back the plunger up to the line showing the required dose.
  • Push the needle through the bottle’s rubber top and push in the air.
  • Turn the bottle and syringe upside down and draw in the required dose using the plunger
  • Pinch up some skin in the chosen area and insert the needle.
  • Push the plunger till the syringe is empty and hold in place for five seconds.
  • Let go of the pinched skin and withdraw the needle.
  • Press the insertion point for a few seconds if there is blood or insulin oozing out, but do not rub the area.

Prefilled pens

  • Roll the pen between the palms 10 times and invert it upside down 10 times.
  • Twist the needle on to the pen, dial 2 units to avoid air, hold the pen with its needle pointing up and tap the cartridge gently to get rid of air bubbles.
  • Use the plunger to make sure the insulin comes out.
  • Turn the dose selector dial back to zero and dial the number for the required dose.
  • Inject the dose, hold the needle in place for six seconds and withdraw. Do not rub the area.

Mixing two insulins

If two insulins are mixed, the required dose of both can be drawn in one syringe and taken as a single injection. If regular insulin is mixed with cloudy insulin, regular insulin should be first drawn into the syringe. The mixture must be injected immediately.


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What are the commonly used insulin products?

Some of the commonly used insulin products are as follows:


  • Insulin aspart (NovoLog)
  • Insulin aspart with niacinamide (Fiasp)
  • Insulin lispro (Humalog)


  • Insulin regular (Humulin R, Novolin R)


  • Insulin NPH (Humulin N, Novolin N)


  • Insulin detemir (Levemir)


Insulin combination products

  • Insulin aspart protamine/Insulin aspart
    • Novolog Mix 50/50
    • Novolog Mix 70/30
  • Insulin lispro protamine/Insulin lispro
    • Humalog Mix 50/50
    • Humalog Mix 75/25
  • Insulin NPH/Insulin regular
    • Humulin 70/30
    • Novolin 70/30

What are the side effects of insulin injections?

The major side effects of insulin injections are:

  • Hypoglycemia
  • Weight gain when you first start using it
  • Lumps or scars from too many injections
  • Rash at the injection site
  • Rash all over the body (rare)

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