Kent Peterson, senior editor, has also produced award-winning work in television and radio.

These days, lots of medicines come with a list of possible side effects that’s so long you might wonder if the drug is worth taking. What about insulin?

Luckily, insulin has very few side effects for most people. Still, it’s important to know what they are.

How insulin helps

Insulin is a hormone that’s made in the body. It helps regulate the amount of glucose in your bloodstream (blood sugar). When people with diabetes can’t make enough insulin or can’t use it efficiently, insulin from the pharmacy can help. Everyone who has type 1 diabetes needs to use insulin, and many people with type 2 diabetes benefit from it too.

The first insulin used to treat humans came from animals. Today in the United States, animal insulin has been replaced by synthetic human insulin manufactured in laboratories. Insulin usually comes as a liquid that’s injected. Inhaled rapid-acting insulin is also available.

There are several different types of insulin that vary according to how quickly they start to work, how long it takes them to reach full strength, and how long they last. Doctors often recommend using more than one type of insulin to achieve the best blood glucose control.

Highs and lows

Because insulin has powerful effects on blood glucose levels, it’s important to take the right amount at the right time as directed by your healthcare provider.

Among the most common side effects of insulin are blood glucose levels that swing too low (hypoglycemia) or too high (hyperglycemia), caused by taking too much or too little insulin. These side effects could be harmful, but they can be prevented and treated.

You can minimize how often you have insulin-related highs and lows. Monitor the way your body responds to insulin and work with your healthcare provider to find the most effective insulin regimen for your unique needs. That will improve your ability to keep blood glucose levels in your target range. Prescription diabetes pills may also help.

Watching your weight

Some people notice another unwelcome side effect: they seem to gain weight while using insulin, especially at first. Meanwhile, other people with poorly controlled diabetes, who either don’t use insulin or aren’t using it properly, may seem to lose weight. But that doesn’t mean ignoring your diabetes care is a good way to drop unwanted pounds. Here’s what’s happening:

Frequent urination is common with poorly controlled diabetes, as the body tries to filter excess glucose from the bloodstream and eliminate it. That could leave you chronically dehydrated without realizing it. You might think you lost weight when you only lost water.

When you start using insulin, your body retains more fluid and it shows up as more pounds on the bathroom scale. At the same time, insulin helps your body do a better job holding on to blood sugar and using it normally instead of excreting it—resulting in increased weight.

Gaining a little weight can actually be a sign that good things are happening from your insulin therapy. But it’s also a reminder to be a little more careful to eat healthy foods and count calories.

Side effects in your skin

A small percentage of people who inject insulin may notice reactions such as these at the injection site:

• Pain
• Swelling
• Redness
• Itching
• Irritation
• Bumps or scars in spots that have had many injections

Tell your doctor or pharmacist if any of these side effects persist or gets worse.


It’s rare to have a severe allergic reaction to insulin, but if it happens, it could be serious. Seek immediate medical care if you notice any of these signs:

• Rash spreading over the body
• Difficulty breathing
• Dizziness
• Swelling or itching, particularly if it’s on the face, tongue, or throat

How inhaled insulin differs

People who use inhaled insulin don’t have to worry about injection-site skin reactions. But they are at risk for the same blood glucose highs and lows and severe allergic reactions that may affect injected-insulin users.

Some inhaled-insulin users also notice a cough or sore throat. There’s no need to see a doctor about them unless they persist or bother you.

Notice something else?

Regardless of whether you inhale or inject your insulin, if you experience any other possible side effects, speak up! It’s important for your healthcare provider to know about them.

Insulin is worthwhile

It’s worth repeating that most side effects only affect a small percentage of insulin users. Most people will never have serious side effects from insulin. The insulin you inject is almost identical to insulin made in the body, so it’s hard to think of a more natural medicine.

Used properly, insulin is a safe and powerful tool for improving diabetes control, avoiding complications, and helping you live a longer and healthier life.

Insulin users, we’d like to hear from you! Add a comment below to share your experiences and thoughts about insulin.