The amount of time it takes for insulin to work depends on the type of insulin, the brand, the site of injection, and other factors.

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Because every person is different, the way your body responds to insulin may not be the same as someone else’s. The type of insulin you take and many factors can influence how rapidly insulin works in your body and how long it stays.

Read on to learn more about insulin and how certain things can affect its absorption.

Insulin is produced naturally in the body by the pancreas. Your pancreas contains millions of beta cells — these cells are responsible for making insulin.

Whenever you eat food with carbohydrates, the beta cells typically release insulin so that other cells in your body can use the blood glucose it gets from food for energy. In a sense, insulin acts as a key, letting glucose into the cells.

How insulin works without diabetes

In people who do not have diabetes, the body produces insulin after digestion.

The presence of insulin triggers cells to take in glucose and use it as energy. The ability of the cells to respond to insulin is called insulin sensitivity.

What happens to insulin when you have diabetes?

If you have diabetes, your body can’t produce any insulin, enough insulin, or is resistant to it. That means glucose is not able to get into your body’s cells effectively.

This inability of the cells to absorb glucose in blood causes elevated blood sugar levels.

Blood sugar levels may be high after meals. They may also be high between meals since the liver makes glucose when we’re between meals or sleeping.

People who have diabetes often give themselves insulin injections or use inhaled insulin to improve their blood sugar levels.

Insulin exists in suspension form and comes in different strengths. The standard strength used in the United States is U-100. This means that it contains 100 units of insulin per milliliter of liquid.

While the strength of insulin varies, its action depends on three characteristics: onset, peak time, and duration.

  • Onset refers to the length of time it takes for the insulin to start lowering blood sugar levels.
  • Peak time is the time when the insulin is at its maximum effectiveness in lowering blood sugar levels.
  • Duration refers to how long the insulin continues to lower blood sugar levels.

Insulin is a protein. Injecting it under the fat of the skin effectively transports it to the blood. Insulin is not available in pill form because your digestive enzymes can break it down, making it ineffective.

There are several different types of insulin available for people who have diabetes. If you’re prescribed insulin, be sure to check the dosing on the prescribing information for your specific brand of insulin.

Rapid-acting insulin

Rapid-acting insulin starts to work shortly after being injected and is typically taken right before a meal. The exact time it takes for rapid-acting insulin to work can depend on the brand.

According to the Centers for Disease Control and Prevention (CDC), it generally takes effect:

  • Onset: 15 minutes
  • Peak: 1 hour
  • Duration: 2–4 hours

Examples of rapid-acting insulin include:

According to research in 2020, for people with type 1 diabetes, lispro (Humalog) typically took effect 31 minutes after injection with a duration between 5.7 to 6.6 hours.

For people with type 2 diabetes, it typically took effect after 45 minutes and lasted about 6.7 hours. The peak time for lispro (Humalog) is about 30 to 90 minutes.

Regular-acting insulin

Also called short-acting insulin, this type of insulin is often taken 30 to 60 minutes before a meal. The CDC notes that it generally takes effect:

  • Onset: 30 minutes
  • Peak: 2–3 hours
  • Duration: 3–6 hours

Examples of short-acting insulin include:

Intermediate-acting insulin

This type of insulin is used overnight or for a half day of insulin. It can be used with rapid- or short-acting insulin. Intermediate-acting insulin tends to take effect:

  • Onset: 2–4 hours
  • Peak: 4–12 hours
  • Duration: 12–18 hours
  • Time to peak plasma: 6–10 hours

Examples of intermediate-acting insulin include Novolin N and Humulin N.

Long-acting insulin

This type of insulin can provide insulin for a full day. These insulins do not peak but are steady throughout the day.

In general, long-acting insulin takes effect:

  • Onset: 2 hours
  • Peak: None
  • Duration: Up to 24 hours

Examples of long-acting insulin include glargine (Lantus) and detemir (Levemir).

Ultra long-acting insulin

This type of insulin provides insulin for longer periods. These insulins do not peak but are steady throughout their period of effectiveness.

In general, ultra long-acting insulin takes effect:

  • Onset: 6 hours
  • Peak: None
  • Duration: 36 hours or longer

Examples of this type of insulin include glargine U300 (IGlar 300) and insulin degludec (IDeg 100 and IDeg 200).

Inhaled insulin

Inhaled insulin was introduced in 2015. It’s fast-acting and is usually taken just before a meal.

It typically takes effect:

  • Onset: 15 minutes
  • Peak: 30 minutes
  • Duration: 3 hours

Researchers have pointed out that the behavior of insulin after administration can vary. This means that there is a tendency for insulin not to follow the standard onset for it to start working.

Several factors can influence the absorption of insulin.

Site of injection

People with diabetes typically use three regions as the injection sites for their insulin: the upper arm, upper leg, and abdomen.

Out of the three sites, the abdomen results in the most effective and rapid absorption of insulin, according to the American Diabetes Association (ADA). The upper leg region results in the slowest.

Concentration of insulin

The higher the insulin concentration, the more rapid the diffusion and rate of absorption. The most common insulin formulation is U-100, but other concentrations are available:

  • U-500
  • Humalog U-200
  • Glargine U-300 (Toujeo)
  • Detemir U-200 (Tresiba)
  • insulin lispro aabc U-200 (Lyumjev)
  • U-40, which is no longer manufactured

Frequency of injection site use

When you inject insulin with a syringe or pen, it’s injected into the layer of fatty tissue just underneath the skin. If you give your injection close to the same place each time, you may develop hard lumps or fatty deposits. This can affect the absorption of insulin.

In people who have to inject large doses several times per day, this may become an issue.

Talk with a doctor for information about where to inject insulin.

Physical factors

Physical factors that increase blood flow can speed up the absorption of insulin. These may include:

  • exercise
  • saunas
  • hot baths
  • massaging the injection site
  • heat exposure

Insulin absorption is reduced by smoking.

How exactly insulin works can vary from person to person. Therefore, it’s important to know what physical and lifestyle factors will affect how insulin acts in your body and how it works to lower your blood sugar levels.