For people with type 1 diabetes and for some with type 2, daily insulin injections are absolutely critical. 

But insulin is a very complicated hormone, and taking it on a daily basis requires tremendous attention and management every day.

In this article, we’ll discuss the potential side effects of insulin that anyone taking it should know.

Insulin Side Effects: What You Need to Know

What is insulin and why do you need it?

First of all, let’s make sure we all understand what insulin is and why it is a crucial part of what keeps you healthy and alive. Without any, you will die. Without enough, you will get very sick and eventually die.

Insulin is a peptide hormone produced by the beta cells of the pancreas. It’s secreted when the “GLUT2 transporter” detects a change in the “serum glucose level.” 

In other words, as your blood sugar starts to rise, your pancreas secretes more insulin to ensure that your blood sugar doesn’t get too high. The insulin takes the glucose in your bloodstream and carries it to cells throughout your entire body that uses it for energy.

Your pancreas also secretes a steady drip of insulin 24 hours a day to meet your “background” insulin needs. Your body needs insulin every hour of every day in order to maintain normal blood sugar levels and function properly.

Even your brain relies on a second-by-second delivery of glucose in order to function — without insulin, your brain cannot make use of the glucose sitting in your bloodstream.

Even if you eat zero sugar or zero grams of carbohydrates, your body still needs insulin to survive.

In people with type 1 diabetes

In a person with type 1 diabetes, your immune system begins attacking and destroying most or all of your beta cells. Every day, your body is trying to produce insulin via the beta cells from your pancreas. And every day, your immune system continues to destroy them.

When a person develops type 1 diabetes, they generally become very sick very quickly — over the course of a few weeks or months — as blood sugar levels rise to life-threatening levels. 

People with type 1 diabetes must take insulin every single day either via an insulin pump or pod or via multiple daily injections with a syringe or insulin pen. Skipping an injection or a whole day of insulin could potentially be fatal.

In people with type 2 diabetes

In a person with type 2 diabetes, the body is either struggling to produce healthy beta cells, or the body is struggling with severe insulin resistance, making it difficult to maintain normal blood sugar levels.

The development of type 2 diabetes usually occurs over the course of months and years, first presenting as prediabetes until blood sugar levels are high enough to qualify as type 2 diabetes.

Some people with type 2 diabetes can improve (or “reverse”) their blood sugars through changes in their nutrition, exercise, and weight. 

However, many patients with type 2 diabetes are struggling to produce healthy beta cells which means they will need some type of medication to bring blood sugars down to a healthy level. For many, the best option may be insulin injections via a syringe or pen.

Common side effects of insulin

Keep in mind that most of the side effects of insulin are actually the result of inaccurate doses and improper injection practices. When taken with great care and careful management, insulin is a critical part of what keeps you alive and healthy.

Low blood sugar

While the human body needs insulin to stay alive, too much can lead to low blood sugars (also known as “hypoglycemia”). Even one unit too much can lead to uncomfortable and dangerous symptoms

Symptoms of low blood sugar include:

  • Feeling shaky
  • Being nervous or anxious
  • Sweating, chills, and clamminess
  • Irritability or impatience
  • Confusion
  • Fast heartbeat
  • Feeling lightheaded or dizzy
  • Hunger
  • Nausea
  • Color draining from the skin (pallor)
  • Feeling Sleepy
  • Feeling weak or having no energy
  • Blurred/impaired vision
  • Tingling or numbness in the lips, tongue, or cheeks
  • Headaches
  • Coordination problems, clumsiness
  • Nightmares or crying out during sleep
  • Seizures

Read more on how to treat low blood sugars.


Lipohypertrophy is a common side effect of long-term insulin injections or insulin pump infusion sites.

Lipohypertrophy is essentially a swollen lump of fatty tissue at the site of frequent injections. Insulin can actually cause the size of fat cells near frequent injection sites to increase.

Scar tissue also usually develops at these locations because both are the result of frequent insulin injections.

In earlier years, when only human insulin was available, lipoatrophy was a similar issue of taking insulin but has since disappeared because human insulin is no longer used by most people.

Using a device to “roll” the tissue most commonly used for injections can help to prevent and break down lipohypertrophy lumps, but for those taking insulin every day, these lumps are inevitable to some degree.

The best thing you can do to minimize the development of lipohypertrophy is to consistently rotate where you inject insulin. Using the same location of your body over and over is going to create lumps from lipohypertrophy and scar tissue.

Identifying areas affected by lipophypertrophy is also important because insulin will not be absorbed well at those sites. These lumps should tell you to start using different areas for your injections or infusion sites and improve your “injection site rotation” habits to prevent future issues.


Some insulin can burn during or immediately after injection. This is common in long-acting insulins like Lantus and Basalgar because they have a high acidity level. 

Other insulin could sting or burn if you injected into muscle tissue rather than body fat, or if you simply hit a sensitive area or an area used too frequently for injections that need to heal.

Preventing the burning sensation from acidic insulins, however, is tricky. Some recommend placing an ice pack on the area before injecting. It can help but it likely won’t eliminate the burning sensation entirely.

Rash and allergic reaction

Less than 4 percent of people with diabetes have a hypersensitivity or allergy to insulin, but if you’re one of those 4 percent, it’s a significant challenge. 

It’s believed that a person’s allergic reaction is in response to additives and peptides within commercially manufactured insulin.

The symptoms of an insulin allergy include:

  • Swelling at the injection site
  • Intense rash, hives, and itching
  • Low blood pressure
  • Swelling within your throat and mouth
  • Difficulty breathing (anaphylaxis)

“Insulin allergies can be local or systemic, as well as immediate or delayed,” explains a 2016 study. “The underlying mechanisms of insulin-associated allergy can be divided into three types: type I (IgE-mediated), type III (IgG-mediated immune complex), and type IV (T-cell-mediated delayed-type) hypersensitivity. Type I hypersensitivity, which manifests as local edema, itching, wheals, and flares, is the most common form.” 

To date, there is no single treatment method that has proven effective enough to be widely used.

Various treatment options, ranging from symptom relief using simple antihistaminics to more complicated insulin desensitization therapy, have been advocated for managing allergic reactions to insulin,” explains the study.

While steroids can also significantly help with the allergic reaction, they create tremendous insulin resistance and make blood sugar management very difficult, so it’s not a realistic long-term solution. 


Rotating your injection sites is crucial in preventing the build-up of scar tissue. If you inject into the same area of your body over and over every day, your body will build up a harder fibrous tissue every time it heals from the injury of that injection. 

Over time that build-up of scar tissue will interfere with your body’s ability to properly absorb the insulin you injected, leading to high blood sugar levels.

By making an effort to inject in different areas of the body (thigh, belly, back of the arm, buttocks, etc.) and different parts of each area (upper thigh vs. lower thigh, etc.) you can prevent the rapid build-up of scar tissue. 

For those who take multiple injections each day or those who use insulin pumps, some scar tissue is inevitable.

Bruising & site irritation

Sometimes, you just hit the wrong spot with your syringe or pen needle, and it creates a small bruise. Insulin pumps and pods can create bruising as well. 

The solution is fairly simple: rotation, rotation, rotation. Rotating your injection sites can help prevent creating too much damage to one area. 

If you notice a bruise or an irritated injection site, try to avoid that particular site (and around it) for the next week or two so it can heal. 

If the irritation persists or the bruising spreads instead of minimizes, contact your healthcare team immediately or visit an Urgent Care clinic to be sure it hasn’t become infected.


While that syringe or insulin pen needle may seem small, it’s still very capable of creating the potential for infection. 

The type of bacteria that most commonly causes infections in areas where insulin is being administered via injection or pump is called “mycobacterium chelonae.”

The higher your blood sugars and HbA1c are, the more at risk you are for developing an infection because those persistently high levels are going to promote the growth of bacteria and impair your immune system.

Using an alcohol swab on the site you’re going to inject or where you’ll place your new infusion set for your pump can help to prevent infections. It’s also critical to use syringes only once.


We all need insulin to live, but excessive or higher amounts of insulin can lead to your body storing more glucose as body fat. The need for higher amounts of insulin is caused generally by:

Insulin resistance, which then requires you to need more and more insulin in order to maintain healthy blood sugar levels.

Beta-cell dysfunction in people with type 2 diabetes is the gradual deterioration of your body’s ability to produce healthy beta-cells. This inevitably means that taking injections of insulin is going to be part of what keeps you healthy and alive. 

Hormones! If you are a growing young adult, your insulin needs are going to go up. This really shouldn’t lead to weight gain unless your other lifestyle habits are increasing your insulin needs. Growth hormones make everyone more insulin resistant and this is a normal part of the human body’s process during puberty. For young women, hormone fluctuations during their menstrual cycle can also create temporary insulin resistance. 

Striving to lessen your insulin needs while still keeping blood sugar levels safe and healthy comes down to improving insulin resistance. For some, this can be done by getting more exercise, losing weight, and improving nutrition habits. 

For many others, though, your body may need support from a diabetes medication to increase your sensitivity to insulin while you work on the aforementioned lifestyle habits. 

“I started noticing a lot of weight gain I couldn’t find the cause of. My new doctor explained that having such high doses of insulin can cause your body to retain weight. Especially as we get older because we are less active. I wish I had known more about how to work with my insulin and diabetes and make it work for my lifestyle.” 

Faith Riddell-Harding (read Faith’s story of starting on insulin)

Cough (inhaled insulin)

Inhaled insulin isn’t nearly as common as injectable insulin, but it’s gaining popularity. While it can be a great addition to your diabetes management plan, it can create a persistent cough in some.

While there are studies in progress assessing the impact of inhaled insulin on a patient’s lungs, it hasn’t existed long enough to truly determine its safety yet.

If you feel that inhaled insulin is irritating your throat, mouth, or lungs, contact your healthcare team immediately.


Yes, an overdose of insulin can be fatal. This is why anyone taking insulin should check their blood sugars several times per day.

Our insulin doses are an estimate based on our weight, activity level, age, diet, and current blood sugar levels. If you are experiencing frequent low blood sugars in the 1 to 3 hours after eating, you’re likely getting too much insulin with your meals. If you’re experiencing frequent low blood sugars in the middle of the night, you may be getting too much insulin with your last meal or too much long-acting/basal insulin.

Talk to your doctor immediately if you suspect you’re experiencing frequent low blood sugars.

It’s also critical to keep fast-acting carbohydrates with you at all times as a person taking insulin. 

At the end of the day, insulin is an essential ingredient in staying alive. But it should be taken and managed with great care in order to prevent the majority of these side effects. Work with your healthcare team, a diabetes educator, and other resources to ensure that insulin is improving your health, not harming it.