6 Insulin Side Effects You Should Know About
Key takeaways:
There are many types of insulin available that work at different speeds to treat diabetes. No matter if they’re rapid-, intermediate-, or long-acting, they all have similar side effects to be aware of.
Common insulin side effects include hypoglycemia (low blood glucose), injection site reactions, and weight gain. Rare side effects of insulin are lipodystrophy (abnormal fat distribution) and swelling in the arms and legs.
It’s important to check your blood glucose regularly while taking insulin. You should inform your healthcare provider about any concerns that you’re experiencing.
Table of contents
Every lock needs the right key to open it. Without the right key, the lock prevents any movement in and out of the door. This image paints a picture of what happens in diabetes.
Insulin is a hormone that’s made and released by your pancreas. It’s the key that opens up the lock to your cells and lets blood glucose (sugar) move inside. This is the way that blood sugar can properly be used as energy. But if you have diabetes, your body may not be able to navigate this process on its own. You may need to take insulin as a daily medication to act as the key to control your blood glucose.
There are many types of insulin available for you to choose from. They work at different speeds and are injected at different times throughout the day. Some examples include rapid-acting insulins like lispro (Humalog), intermediate-acting insulins like human insulin (Humulin N), and long-acting insulins like glargine (Lantus).
But, insulins serve the same purpose overall — to lower blood glucose. They also have similar interactions and similar side effects.
1. Low blood glucose
Insulin is intended to lower your blood glucose, but sometimes its effects can be more powerful than you need. Low blood glucose (hypoglycemia) is the most common insulin side effect. This is when your blood glucose drops below 70 mg/dL.
Having blood glucose this low can feel like any of these symptoms:
Shakiness
Sweating
Dizziness or lightheadedness
Confusion
Fast heartbeat
Hunger
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If you feel any of these symptoms, it’s important to check your blood glucose right away. If it’s below 70 mg/dL, follow the “15-15 rule.” This means you should eat or drink 15 g of fast-acting carbohydrates. This could include 3 to 4 glucose tablets, ½ cup of fruit juice or regular soda, or 1 tbsp of sugar.
Then, recheck your glucose in 15 minutes. If it’s still below 70 mg/dL, you can repeat this process. If you still don’t respond to fast-acting carbohydrates by this time or your glucose is below 55 mg/dL, it’s important to get emergency medical help.
To prevent hypoglycemia with insulin, it’s important to take the right dose.
Talk to your healthcare provider about adjusting your units of insulin to keep your blood glucose in the normal range. This range is generally between 80 mg/dL to 130 mg/dL before meals or less than 180 mg/dL 2 hours after a meal. Finding your right dose can take some trial and error and gradual dose adjustments.
2. Injection site reactions
Injecting insulin can lead to pain or discomfort at the site of your injection. It may also swell, itch, or turn red. This is called an injection site reaction. Most of the time these reactions are minor irritations caused by the injection. They’re not considered allergic reactions.
What’s more, injection site reactions are typically not concerning. They’re a temporary problem that should get better on their own. To relieve some of the discomfort, you can apply an ice-pack, warm compress, or take an anti-itch medication like diphenhydramine (Benadryl).
To lower the possibility of having this reaction, it’s important to rotate the spot where you inject and bring the insulin to room temperature before injection. Injecting insulin while it’s cold can be more painful.
3. Weight gain
Insulin can cause weight gain. When insulin helps your cells soak up extra glucose from your blood, that glucose is converted into fat. This ultimately helps your body use its sugar supply better, but it can lead to weight gain.
People with diabetes who take insulin can gain an average of 4 lbs (2 kg) in the first year they start insulin. To prevent this type of weight gain, it’s important to pair insulin with a diabetes-friendly diet and regular exercise. These lifestyle changes can also better manage blood glucose and overall diabetes health.
If you see that you’ve gained weight after starting insulin, talk to your healthcare provider for added guidance on lifestyle changes.
4. Headache
It’s possible to develop headaches after starting or changing your insulin dose. While low or high blood glucose levels can cause headaches, a big change in your blood glucose could also be the culprit.
Having a headache may not need quick medical help, but it’s still an important side effect to know about. You can take an over-the-counter medication like ibuprofen (Advil, Motrin) or acetaminophen (Tylenol) to manage the pain. But once you get used to insulin and your blood glucose levels stabilize, headaches will generally improve.
If you keep having headaches or they get worse at any point, there could be another cause. Talk with your healthcare provider about finding the cause and helping treat the headache.
5. Lipodystrophy
Lipodystrophy is when there is a problem with fat distribution in the body. There are two types of lipodystrophy that insulin can cause: lipoatrophy (loss of fat or pits in the skin) or lipohypertrophy (enlargement of the fat or thickened skin). When this happens, it usually shows at the spot where insulin was injected.
It’s important to rotate your injection site to help avoid lipodystrophy. Injecting into areas with abnormal fat distribution can also affect how well blood glucose is controlled. That’s another reason why rotating injection sites is key to healthy and safe insulin use.
6. Swelling in your arms and legs
Insulin can cause your body to retain sodium and fluid, also known as edema. Holding on to excessive fluid can especially affect your arms and legs.
This is a rare insulin side effect, and it usually goes away on its own. Your healthcare provider may recommend lifestyle changes for short-term relief, such as elevating your legs above the level of your heart and limiting salt in your diet.
But if these tips don’t help or if you experience swelling that continues, your healthcare provider may adjust your dose or suggest starting a diuretic (“water pill”).
When should I contact my healthcare provider about side effects from insulin?
Many side effects caused by insulin resolve on their own as your body gets used to the medication. If your side effects don’t improve within a few weeks or if they worsen, discuss this with your healthcare provider. They may be able to adjust the dose or change the type of insulin to better suit your needs.
Insulin is a lifesaving medication. Don’t stop taking insulin on your own without talking to your healthcare provider first.
Keep in mind: Side effects between the various types of insulins might slightly vary. It’s a good idea to talk with your healthcare provider or pharmacist about any concerns specific to the insulin product you’re using.
The bottom line
Insulin’s most common side effects are hypoglycemia, injection site reactions, and weight gain. Side effects like lipodystrophy and edema are rarer, but possible. Thankfully, most of insulin’s side effects should get better with time. Talk to your healthcare provider about any concerns you may have with taking insulin.
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References
Akinci, B., et al. (2018). Lipodystrophy syndromes: Presentation and treatment. Endotext.
American Diabetes Association. (n.d.). Hypoglycemia (low blood glucose).
Association of Diabetes Care & Education Specialists. (2020). Pro tips (and tricks) for easier and better insulin injections.
Centers for Disease Control and Prevention. (2022). How to treat low blood sugar (hypoglycemia).
Endocrine Society. (2022). Pancreas hormones.
RemedyRepack Inc. (2022). Insulin aspart [package insert].
