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A Beginner’s Guide to Insulin: How long does it take insulin to work and more.

Hi there, friend with diabetes. Let’s talk insulin. Whether you were just recently sent home with some insulin pens and a prayer or you are someone who’s been using insulin for a while but realized you really need a review of the basics, you’re in the right place. In this post, I’ll discuss the very basics of this tool in your diabetes kit.

Insulin Stigma

We’ve gotta start here, friend. This is one of the first questions I ask my clients:

How do you feel about taking insulin?

No matter what type of diabetes you’re living with, insulin gets a bad rap. You may have read somewhere that insulin makes you a failure and you should avoid it. Or maybe you have a relative who insists “insulin will make you fat.”

I’m here to clear the air, and I want you to listen:

If you are at the point where your body is not producing enough or any insulin, then this is 100% necessary for your body to function.

You are not a failure, friend. You deserve good health, and you are worthy of the tools to get you there.

Now, I know there are lots of questions about weight gain when starting insulin. When your body is without insulin, it is unable to use the glucose in your blood. Glucose is the main source of energy for the cells in our body. When your body can’t use that glucose, it resorts to breaking down fat and muscle²

The weight gained from starting insulin is often a “sigh of relief” from your once starved and panicked body.

Your body is healing.

This isn’t to say that your disappointment or nervousness about any gained weight isn’t valid — we can talk about this in the future. But for right now, you are healing and learning to live with diabetes, and that is 100% OK.

What Does Insulin Do?

Insulin is a hormone. Beta cells in the pancreas are responsible for secretion of insulin. It converts the glucose from your food into energy for your cells to function. With diabetes, insulin production and/or the use of the insulin is malfunctioning. Someone with autoimmune diabetes (think Type 1, LADA, certain types of MODY) or someone who had to have their pancreas removed, does not have functioning beta cells.

This means they must inject insulin to live.

Type 2 diabetes involves resistance to insulin. This means the body is not using insulin the way it should. People with Type 2 diabetes can also experience beta cell death. At this point, they may need to start injecting insulin to supplement this loss.

There are different types of insulin available for different purposes. Everyone needs insulin to do the following:

  1. Keep blood glucose (BG) steady after meals

  2. Keep blood glucose steady in a fasted (no food digesting) stat

For the first purpose, someone would need to be prescribed rapid or short acting insulin. For “background” insulin, someone will be prescribed intermediate acting or long acting insulin³

Types of insulin available in the US

  • Rapid acting insulin is the fastest acting insulin. This is typically taken before meals or used to correct an above target blood sugar.

  • Short acting insulin can also be used for the same purposes, although it is slower acting than rapid. Reasons to use this insulin would be for keeping costs lower and also for those who are eating lower carbohydrate high-fat diets.

  • Intermediate acting insulin is much slower absorbing than the rapid and short acting insulins and is therefore used to keep the BG steady during a fasted state similar to long acting. The duration is 12 hours, so it is typically prescribed twice a day to cover the person’s background insulin needs. Some people with diabetes (PWD) like to use this if they need a temporary increase in basal coverage like after eating a high fat meal. It also tends to be less expensive than its long acting counterparts.

  • Long acting insulin lasts the longest in the body out of all of the insulins and it is used to keep the BG steady in a fasted state. This insulin helps to cover the stored glucose released by your liver.

Insulin action time can be thought of as onset, peak, and duration. The onset is typically when you will see the insulin start working. The peak is the time when the insulin is at its most “potent.” And the duration is the length of time it stays effective in the body. Understanding these can help you figure out how long it takes insulin to start working and how to use it to your advantage.

A chart with how long it takes insulin to work, peak, and how long it stays in the system

Note that our bodies metabolize insulin differently, so use these times as a baseline.

The activity profiles of different types of insulin

(University of California, San Francisco, 2007, figure 1)

The reason it is important to understand the action timing of short acting insulin is so that you can line up the digestion of food with the timing of the insulin. This results in the least impact on your blood sugar. If you take insulin too late, this can result in a significant rise in blood sugar. If you take insulin too early, this can cause a drop in blood sugar. Talk with your diabetes educator about how you should time your insulin and your meals for best results.


Methods of Insulin Administration

Insulin is injected under a layer of fat below the skin using a needle. Insulin can also be inhaled using a special powdered form as well as infused intravenously when in the hospital. Majority of people will learn to self inject using a pen, vial, or insulin pump.

Syringe and Vials

This OG method of insulin injection is not as common since the advent of pumps and pens. But it is important to know how to use a syringe and vial in case of an emergency. Syringes vary in regards to the amount of insulin they hold and the needle length³. Vials hold up to 1,000 units of insulin or more depending on the type of insulin you are using.

Syringe and vials can be a more economical option for some people and can also be better for those taking a significant amount of insulin. Syringes can also inject half units which is helpful for more insulin sensitive people who need fractions of a dose.

Insulin Pens

Pens have grown in popularity over the decades:

  • They cut down on medical waste as you only need to change out the needle with each use³

  • They tend to be a bit more portable (you could stick one in your front pocket like a ball point pen!)

  • They are easier to use in general or especially for people with dexterity or vision disabilities

Insulin pens come in different concentrations like vials but majority of the pens hold 300 units at once. Electronic pens are also on the market which allow the user to calculate doses easily, track their injections on their phone, and utilize half units (regular pens only dose up in 1 unit increments).

Insulin Pumps

Insulin pumps are electronic devices that deliver insulin into the fat layer using a flexible plastic tube³. This tube is inserted every 2–3 days by the user. When using an insulin pump, you will not need to use long-acting insulin because the pump delivers a continuous stream of basal dose insulin. This basal insulin can be adjusted much more easily and customize-ably than with long acting insulin.

For example, let’s say you take 24 units of long-acting insulin every day as your long acting insulin. This is about 1 unit of insulin every hour. But you may find that you need more insulin in the morning than at night. To cover the morning rise, you can’t increase the 24 units too much though because that will result in hypoglycemia in the evening.

An insulin pump fixes this dilemma because it allows you to spread out that 24 units however you need. So you can take 1.5 units per hour for the first 6 hours of the morning, and bring the dose down as you become more sensitive in the evening. This prevents over medication and unnecessary hypoglycemia.

Alongside the basal profiles, your insulin pump is used to correct blood sugars and give insulin before meals. We refer to these larger doses up front as boluses.

Insulin pumps also have the advantage of delivering very small doses of insulin. Think 0.05 units at a time! This is great for people who don’t need as much insulin or for those who desire tighter control of their blood sugars.

Pumps definitely have more of a learning curve than the other methods though and they run the risk of mechanical failures. This can result in complications if not monitored appropriately. Supplies and the pumps themselves also tend to be more inaccessible and expensive.


Well, there you have it, friend. A beginners guide to insulin. If you are new to insulin or are feeling overwhelmed in anyway, consider working with me for more individualized help!


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