If you’re looking for treatment options to manage your diabetes, your doctor might suggest NovoLog. It’s a prescription drug used to manage blood sugar levels in adults and children with diabetes mellitus. It’s a fast-acting insulin for type 1 or type 2 diabetes that you’ll likely use long term.

NovoLog comes as a liquid solution that you’ll inject under your skin. There are several forms of the drug:

  • NovoLog FlexPen* (prefilled, disposable insulin pen)
  • NovoLog PenFill (insulin-filled cartridges that are used with a reusable insulin pen)
  • NovoLog vial (used with syringes or an insulin pump)

You may receive NovoLog by intravenous (IV) infusion (an injection into your vein given over time) if your condition is being treated in a hospital.

The active ingredient in NovoLog is insulin aspart. (An active ingredient is what makes a drug work.) It’s a certain kind of biologic, which is a drug made in a laboratory from living cells.

For more information about NovoLog, including details about its uses, see this in-depth article.

Like other drugs, NovoLog can cause mild to serious side effects (also called adverse effects). Keep reading to learn more.

* NovoLog FlexPen replaced the NovoLog FlexTouch prefilled pen, which is no longer available.

Some people may experience mild to serious side effects during their NovoLog treatment. They don’t happen to everyone, but examples of commonly reported side effects include:

* To learn more about this side effect, see the “Side effects explained” section below.

The sections below contain more information about some of NovoLog’s mild and serious side effects.

Some people have mild side effects while using NovoLog. Examples that have been reported include:

* To learn more about this side effect, see the “Side effects explained” section below.

In most cases, these side effects should be temporary. And some may be easily managed. But if you have symptoms that are ongoing or bother you, talk with your doctor or pharmacist. And do not stop using NovoLog unless your doctor recommends it.

NovoLog may cause mild side effects other than the ones listed above. See the drug’s prescribing information for details.

Note: After the Food and Drug Administration (FDA) approves a drug, it tracks and reviews side effects of the medication. If you’d like to notify the FDA about a side effect you’ve had with NovoLog, visit MedWatch.

NovoLog can cause mild to serious side effects in some people. Serious side effects are less common than mild ones, but they can happen. Serious side effects that have been reported with this drug include:

If you develop serious side effects while taking NovoLog, call your doctor right away. If they seem life threatening or you think you’re having a medical emergency, immediately call 911 or your local emergency number.

* To learn more about this side effect, see the “Side effects explained” section below.

Get answers below to some common questions about NovoLog’s side effects.

Are NovoLog’s side effects similar to the side effects of Fiasp?

Yes, the side effects of NovoLog are similar to those of Fiasp. This is because they contain the same active ingredient, insulin aspart. (An active ingredient is what makes a drug work.) These side effects include:

Unlike NovoLog, Fiasp also contains niacinamide (vitamin B3) and L-arginine (an amino acid) to make it more stable and work faster. The side effects of these two drugs are similar, but some may occur at different rates since Fiasp works faster. For example, low blood sugar can occur more quickly with Fiasp.

To learn more about the side effects of NovoLog compared to Fiasp, talk with your doctor.

Could using too much NovoLog cause side effects?

Yes, taking too much NovoLog can cause side effects. These may be mild to severe, depending on how your body responds to the overdose. To learn more about some of NovoLog’s side effects, see the “Side effects explained” section below.

A NovoLog overdose can cause serious side effects that can be life threatening, such as:

Call your doctor right away if you think you’ve taken too much NovoLog. You can also call 800-222-1222 to reach the American Association of Poison Control Centers or use its online resource. But if you have severe symptoms, immediately call 911 (or your local emergency number) or go to the nearest emergency room.

To learn more about a NovoLog overdose, see this in-depth article.

To help prevent overdose, be sure to take your dose of NovoLog exactly as your doctor prescribes. Using a medication reminder such as an alarm or phone app can help you remember when to take it. It can also help prevent accidental overdose from giving yourself extra injections or injections too close together.

Can I have side effects from using NovoLog in an insulin pump?

It’s possible. Side effects from Novolog are the same whether it’s given by an insulin pen, syringe, or insulin pump. But you may have side effects if the pump malfunctions and gives you the wrong dose. (See “Side effects explained” above to learn more about some of NovoLog’s side effects.) Incorrect NovoLog doses can cause serious side effects, such as:

If you use an insulin pump, your doctor will show you how to give yourself an injection under your skin with a syringe and needle in case of a pump malfunction.

Be sure to follow the operating and care instructions from your doctor and the pump’s manufacturer. The drug’s manufacturer recommends not mixing NovoLog with any other drugs or liquids in the pump. This is to help prevent side effects or drug-related medical problems.

Insulin can spoil if it gets too hot or is left too long in the pump reservoir. This can cause you to have adverse effects such as high blood sugar since NovoLog isn’t working in your body as it should. To prevent spoilage, it’s recommended that you should change the NovoLog in the pump’s reservoir at least every 7 days. Or it may need to be sooner than 7 days if:

  • recommended by the pump’s manufacturer
  • the NovoLog in your pump reservoir has been exposed to a temperature above 37°C (98.6°F)

Talk with your doctor about how to use your insulin pump. They can answer any questions so that you’ll feel confident using a pump for your NovoLog treatment.

Learn more about some of the side effects NovoLog may cause.

Weight gain

Some people may gain weight while using NovoLog. How often this side effect occurred in studies isn’t known. All insulin drugs may cause weight gain as a side effect because of how it works in your body. NovoLog removes sugar from your blood, which your cells use for energy. But some sugar is stored as fat, which your cells will use for energy later. Over time you may gain weight, especially if you have frequent swings in your blood sugar level.

Your dose of NovoLog may need to be adjusted if you gain or lose weight during your treatment.

Sudden weight gain can be dangerous. Your body might be retaining fluids, which can be a symptom of heart failure. Other diabetes drugs called thiazolidinediones can cause or worsen heart failure when taken together with NovoLog. Examples of thiazolidinediones include:

What might help

Regularly monitoring your blood sugar level while using NovoLog can help reduce large swings in your blood sugar that can cause weight gain.

To manage your weight, also try to exercise regularly and eat smaller meals throughout the day. Talk with your doctor about the right amount of daily calories your body needs. They can make recommendations on how to manage your weight while using NovoLog.


Changes in the thickness of your skin near an injection site is called lipodystrophy. The skin appears thick or dimpled due to repeated injections into the same spot. Injecting into these spots can cause the drug to not work properly and lead to hyperglycemia (high blood sugar). And suddenly changing injection sites to an unaffected area of skin can lead to hypoglycemia (low blood sugar).

What might help

To help prevent lipodystrophy, rotate your injection sites each time you use NovoLog. If you use an insulin pump, rotate the infusion sites.

If you notice that your skin looks pitted or thick at your injection site, tell your doctor right away. Before starting NovoLog, talk with your doctor about where to inject the drug and how to rotate sites.


Hypoglycemia (low blood sugar) is the most common side effect caused by NovoLog. The drug works to lower blood sugar, but sometimes it can cause your blood sugar to get too low. This is usually a mild side effect. Symptoms include:

In rare cases, extremely low blood sugar may occur. This is considered a medical emergency and can be life threatening. Some symptoms of severe low blood sugar include:

Your risk of severe low blood sugar increases if you:

  • take NovoLog when your blood sugar is low
  • are fasting
  • take other diabetes drugs along with NovoLog
  • have liver or kidney problems

To learn more about mild to severe low blood sugar, talk with your doctor.

What might help

Regularly monitoring your blood sugar level while using NovoLog can help prevent low blood sugar. Your doctor may recommend that you measure your blood sugar with a portable device called a glucometer. They’ll recommend how often you need to do this based on the type of diabetes you have and your treatment plan.

If you notice signs that your blood sugar is low, you should consume at least 15 grams (g) of carbohydrates. Examples of fast-acting carbohydrates include:

  • hard candy (about 3 to 4 pieces)
  • 4 ounces (oz) (about 1/2 cup) of juice or non-diet soda
  • glucose (sugar) tablets
  • 1 tablespoon of honey

Check your blood sugar again after 15 minutes. Repeat this process until your blood sugar increases to a safe level. If you have symptoms of severe hypoglycemia, you or someone around you should call 911 for emergency help.

Hypokalemia (low potassium level)

NovoLog can cause hypokalemia (low potassium level), which can be life threatening. How often this side effect occurred wasn’t reported in the drug’s studies, but your risk may be higher if you have liver or kidney problems.

Drinking large amounts of alcohol can also lower potassium levels and may increase your risk of this side effect when combined with NovoLog. If you drink alcohol, talk with your doctor before starting this treatment.

Your risk of low potassium can also increase if you use NovoLog while taking certain other drugs that can lower your potassium level. These include:

With low potassium, you may have symptoms such as:

Talk with your doctor if you have concerns about low potassium levels while taking NovoLog.

What might help

Before starting NovoLog, talk with your doctor about any other medications you take and your health history. If you notice any symptoms of low potassium, call your doctor right away. If your potassium level is too low, you’ll likely need to be treated in a hospital.

Allergic reaction

Like most drugs, NovoLog can cause an allergic reaction in some people. Symptoms can be mild to serious and can include:

  • skin rash
  • itchiness
  • flushing (temporary warmth, redness, or deepening of skin color)
  • swelling under your skin, usually in your eyelids, lips, hands, or feet
  • swelling of your mouth, tongue, or throat, which can make it hard to breathe

What might help

If you have mild symptoms of an allergic reaction, such as a mild rash, call your doctor right away. They may suggest a treatment to manage your symptoms. Examples include:

  • an antihistamine you take by mouth, such as Benadryl (diphenhydramine)
  • a product you apply to your skin, such as hydrocortisone cream

If your doctor confirms you’ve had a mild allergic reaction to NovoLog, they’ll decide if you should continue using it.

If you have symptoms of a severe allergic reaction, such as swelling or trouble breathing, call 911 or your local emergency number right away. These symptoms could be life threatening and require immediate medical care.

If your doctor confirms you’ve had a serious allergic reaction to NovoLog, they may have you switch to a different treatment.

Keeping track of side effects

During your NovoLog treatment, consider taking notes on any side effects you’re having. You can then share this information with your doctor. This is especially helpful when you start taking new drugs or using a combination of treatments.

Your side effect notes can include things such as:

  • what dose of the drug you were taking when you had the side effect
  • how soon you had the side effect after starting that dose
  • what your symptoms were
  • how it affected your daily activities
  • what other medications you were taking
  • any other information you feel is important

Keeping notes and sharing them with your doctor will help them learn more about how NovoLog affects you. They can then use this information to adjust your treatment plan if needed.

NovoLog may not be right for you if you have certain medical conditions. (This is known as a drug-condition interaction.) Other factors may also affect whether NovoLog is a good option for you. Talk with your doctor about your health history before starting this drug. Below are a few factors to consider.

Liver or kidney problems. There’s an increased risk of hypoglycemia (low blood sugar) while taking NovoLog if you have liver or kidney problems. If your doctor determines this drug is a safe treatment option for you, they may adjust your dose more often. They may also recommend frequent monitoring of your blood sugar levels.

Allergic reaction. If you’ve had an allergic reaction to NovoLog or any of its ingredients, your doctor will likely not prescribe it for you. Ask them about other treatments that might be better options.

Heart failure. Your risk of heart failure can increase if you use NovoLog while taking diabetes drugs called thiazolidinediones. Sudden weight gain may be a sign of fluid buildup and heart failure. Tell your doctor if you take thiazolidinediones or have new or worsening heart failure while taking this drug. They can recommend a safe treatment plan for you.

Hypokalemia (low potassium level). NovoLog can cause you to have a low level of potassium in your blood. Your risk may increase if you have certain other health conditions or take other medications that can lower your potassium level. Low potassium can cause serious heart problems. If it gets too low, you may need to be treated in a hospital. (See “Side effects explained” above for more information.)

Alcohol and NovoLog

You should avoid using NovoLog with alcohol. Alcohol can decrease NovoLog’s ability to lower your blood sugar. Drinking too much alcohol can cause side effects such as diarrhea and headache, which are also side effects of NovoLog. Using the two together can worsen these side effects.

Talk with your doctor about the amount of alcohol that may be safe for you during your treatment.

Pregnancy and breastfeeding while taking NovoLog

The safety of taking NovoLog while pregnant is unknown. But it’s important to manage your blood sugar if you have diabetes, especially during pregnancy. Talk with your doctor about safe ways to manage your blood sugar level if you’re pregnant or planning to become pregnant.

It’s also unknown if NovoLog can pass into human breast milk or what its effects might be in a breastfed child. Talk with your doctor about safe options for feeding your baby during your NovoLog treatment.

If you have type 1 or type 2 diabetes, talk with your doctor to see if NovoLog is right for you. This drug is known to cause several common side effects. These are usually mild, but serious side effects can happen. Your doctor can provide you with more information. A few questions you might want to ask include:

  • If I have severe side effects, will my treatment with NovoLog be stopped?
  • Will my side effects from NovoLog worsen if I have liver or kidney problems?
  • Does NovoLog have more serious side effects than other kinds of insulin drugs?

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Are NovoLog’s side effects different if it’s used to manage blood sugar levels in type 1 diabetes versus type 2 diabetes?



Possibly. In studies, people with type 1 diabetes reported some different common side effects while using NovoLog than those with type 2 diabetes.

But you may experience different side effects from this drug for other reasons as well, such as from:

  • other medications you take
  • other health conditions you may have
  • how well your diabetes is being managed

The most common side effect of insulin drugs, including NovoLog, is hypoglycemia (low blood sugar). Other side effects that were more common based on diabetes type are listed below.

NovoLog’s common side effects reported by people with type 1 diabetes:

NovoLog’s common side effects reported by people with type 2 diabetes:

Talk with your doctor to learn more about the side effects of NovoLog for your diabetes type.

The Healthline Pharmacist TeamAnswers represent the opinions of our medical experts. All content is strictly informational and should not be considered medical advice.
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Disclaimer: Healthline has made every effort to make certain that all information is factually correct, comprehensive, and up to date. However, this article should not be used as a substitute for the knowledge and expertise of a licensed healthcare professional. You should always consult your doctor or another healthcare professional before taking any medication. The drug information contained herein is subject to change and is not intended to cover all possible uses, directions, precautions, warnings, drug interactions, allergic reactions, or adverse effects. The absence of warnings or other information for a given drug does not indicate that the drug or drug combination is safe, effective, or appropriate for all patients or all specific uses.