The way insulin works can vary from person to person because every person’s body works differently. Several factors can influence how quickly their body responds to insulin and how long it takes to process it.

Some types of insulin, called rapid- or short-acting insulin, can start working within minutes, while long-acting insulin can last an entire day. Doctors can recommend the most appropriate type of insulin depending on several factors, including:

how active you are
your age
how long it takes your body to absorb insulin
your diet
how long insulin stays active in your body
how effectively you can manage your blood sugar levels through food

How long does it take to work?

A person doing a finger prick test to check their blood sugar levels, wondering how long insulin takes to work. — Photography by Prajna Hegde/Getty Images

The amount of time insulin takes to work depends on various factors, including your metabolism and the type of insulin you use.

Doctors classify insulin according to how fast it starts lowering your blood sugar levels (onset) and for how long it keeps working (duration). Diabetes medications also have a different peak time, which is when insulin is at its maximum strength.

People with type 1 diabetes typically take a combination of different insulin medications. People with type 2 diabetes may also need to take insulin to manage their blood sugar levels.

Types of short-acting insulin

There are several types of insulin. Some are rapid-acting and begin working immediately. People usually take these before a meal. Other types are long-acting and can work for more than a day or overnight.

Short-acting insulin

According to the Centers for Disease Control and Prevention (CDC), people typically take short-acting insulin between 30 and 60 minutes before a meal. Short-acting insulin typically works in the following way:

Onset: 30 minutes
Duration: 3-6 hours
Peak: 2-3 hours

Some examples of short-acting insulin include Humulin R and Novolin R.

Rapid-acting insulin

Rapid-acting insulin starts working soon after you have injected it. People usually take this type of insulin just before a meal. According to the CDC, rapid-acting insulin works as follows:

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

Some examples of rapid-acting insulin include aspart (Novolog), glulisine (Apidra), and lispro (Humalog).

Types of long-acting insulin

According to the CDC, three types of insulin can work for a prolonged time:

intermediate-acting insulin
long-acting insulin
ultra-long-acting insulin

Intermediate-acting insulin

You typically take an intermediate-acting insulin, such as Novolin N and Humulin N, overnight or to last about half a day. Intermediate-acting insulin typically works in the following way:

Onset: 2-4 hours
Duration: 12-18 hours
Peak: 4-12 hours

Long-acting insulin

Long-acting insulin, such as glargine (Lantus) and detemir (Levemir), typically works in the following way:

Onset: 2 hours
Duration: up to 24 hours
Peak: none

Ultra-long-lasting insulin

Ultra-long-acting insulin, such as insulin degludec (IDeg 100 and IDeg 200) and glargine U300 (IGlar 300), typically works in the following way:

Onset: 6 hours
Duration: 36 hours or longer
Peak: none

Long-acting and ultra-long-acting insulins can provide insulin for the whole day or more. These types of insulin do not peak but remain at a steady level while they work.

Premixed insulin

Some people may use premixed insulin. This type of insulin combines short-acting and long-acting insulin, and it can benefit people who may have difficulties following or reading instructions due to reduced eyesight or other health conditions.

People usually take premixed insulin 10–30 minutes before eating breakfast and dinner.

Premixed insulins include Humulin 30/70 and Novolin ge 30/70. Premixed insulin typically works in the following way:

Onset: 5–60 minutes
Duration: 10–16 hours
Peak: varies

Inhaled insulin

In 2015, inhaled insulin (Afrezza) became available on the market. People can take this type of rapid-acting insulin right before a meal. Inhaled insulin typically works in the following way:

Onset: 10-15 minutes
Duration: 3 hours
Peak: 30 minutes

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How do you know when it’s working?

Once insulin starts working, it lowers your blood glucose levels. To determine if insulin is working, you can take a finger-prick test or use a flash glucose monitor to check your blood sugar levels.

If you have diabetes or you regularly use insulin, you should periodically check your blood glucose levels to ensure your diabetes remains under control.

Factors that can affect insulin absorption

Several factors can affect how your body absorbs and processes insulin. A 2018 study pointed out how insulin behavior can vary for each person depending on a combination of factors, such as:

Concentration of insulin: Insulin injections come in different concentrations. The higher the concentration, the more rapidly your body absorbs the insulin.
Site of injection: People with diabetes typically inject insulin into three areas of their body: the upper arm, the abdomen, and the upper leg. The abdomen absorbs insulin the most effectively and rapidly, while the upper leg region is the least effective.
Frequency of injection site use: Appropriate injection technique is the basis for maintaining good insulin absorption. If you always inject insulin in the same area of your body, you may develop hard lumps or a fatty deposit under your skin that can affect insulin absorption. People should regularly rotate their insulin injection sites to prevent this from happening.
Physical factors: Certain factors that can increase your blood flow can also encourage faster insulin absorption. This includes:
- hot baths
- exercise
- heat exposure
- massaging the injection site
Smoking: This slows down the absorption of insulin.

It is essential to monitor your blood sugar levels regularly when using insulin.

If you notice high blood sugar levels even after having an insulin injection, contact your doctor to check why this is happening. You may need to switch to a different medication.

Summary

The time it takes for insulin to start working depends on how well your body absorbs insulin and the type of insulin you use. There are several types of insulin. Some types are rapid-acting, which you can take before a meal, while others are long-acting and can work for more than a day.

Doctors can recommend the most appropriate type of insulin based on your health conditions and lifestyle.

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