Nerlynx (neratinib) is a prescription drug used to treat certain types of breast cancer. Nerlynx can cause side effects that range from mild to serious. Examples include diarrhea, nausea, and vomiting.

Specifically, Nerlynx is used in adults to treat certain types of HER2-positive breast cancers. (“HER2” represents human epidermal growth factor receptor 2.) These include the following:

  • Early stage HER2-positive breast cancer: For this condition, Nerlynx is taken alone following treatment with Herceptin (trastuzumab). This further helps reduce the risk of cancer.
  • Advanced HER2-positive breast cancer: For this condition, Nerlynx is taken along with Xeloda (capecitabine). Advanced means the cancer has spread beyond the breast to nearby tissue.

Nerlynx is a type of chemotherapy drug called targeted therapy. It’s not immunotherapy. The drug contains the active ingredient neratinib and comes as an oral tablet.

Keep reading to learn about common, mild, and serious side effects that Nerlynx can cause. For a general overview of the drug, including details about its uses, see this article.

Below are just a few of the more common side effects people reported in Nerlynx studies. These side effects can vary depending on the condition the drug is treating.

More common side effects in people taking Nerlynx alone for early stage HER2-positive breast cancer include:

  • fatigue (low energy)
  • diarrhea
  • rash
  • nausea and vomiting
  • stomach pain

More common side effects in people taking Nerlynx along with Xeloda for advanced HER2-positive breast cancer include:

  • dizziness
  • lack of appetite
  • diarrhea
  • nausea and vomiting
  • weight loss

The following sections include more side effects of Nerlynx. Each person’s experience with side effects may differ.

Mild side effects have been reported with Nerlynx. These include:

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

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

Serious side effects have been reported with Nerlynx. These include:

  • severe diarrhea
  • liver problems
  • fetal harm if taking Nerlynx while pregnant

You can learn more about severe diarrhea and liver problems in the “Side effects explained” section.

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

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 Nerlynx, visit MedWatch.

Allergic reaction

For some people, Nerlynx can cause an allergic reaction. But this side effect wasn’t reported in the drug’s studies.

In general, symptoms of allergic reaction can be mild or serious.

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. They also can determine whether you should continue Nerlynx treatment.

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

Your doctor can confirm whether you’ve had a serious allergic reaction to Nerlynx. If so, they may have you switch to a different treatment.

Get answers to some frequently asked questions about Nerlynx’s side effects.

What are the side effects of Nerlynx vs. Herceptin?

Both Nerlynx and Herceptin have side effects such as:

  • diarrhea
  • nausea
  • fatigue (low energy)
  • rash
  • lack of appetite

Nerlynx itself can cause severe diarrhea and liver issues. In comparison, Herceptin itself can cause serious complications affecting the heart muscles and lungs. Herceptin, which is given by intravenous (IV) infusion (injection into a vein), also has the risk of infusion reaction.

If you have questions about either medication, check with your doctor or pharmacist.

Does Nerlynx cause long-term side effects?

It’s possible. Long-term side effects include those that may start at any time you’re taking a drug. This is true even if you’ve taken it for a long time. It also includes side effects that may not go away, even after you stop taking the drug.

Examples of long-term side effects reported in Nerlynx studies include:

Regular monitoring throughout treatment helps doctors detect liver issues early. Also, once Nerlynx treatment is stopped, liver enzyme levels usually return to normal, which is a sign of recovery.

Severe liver damage is rare. And long-lasting effects depend on the amount of damage to the liver.

Taking Nerlynx while pregnant can cause problems with fetal development (commonly known as birth defects). It also can cause pregnancy loss. If you are pregnant or can become pregnant, you should use effective birth control while taking Nerlynx. You should also use it for some time after completing treatment. If you become pregnant while taking Nerlynx, tell your doctor right away.

Talk with your doctor to learn more about possible side effects of Nerlynx and how long they may last.

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

Mouth sores

Mouth sores or canker sores were a common side effect reported in studies of Nerlynx. Mouth sores may cause symptoms such as:

  • painful round or oval ulcer with a red edge and white center
  • swollen areas under the tongue or on the inside of the cheeks or lips
  • burning or stinging blisters
  • swollen tongue or lips

Factors that can raise the risk of mouth ulcers when taking this drug include:

  • a history of mouth ulcers, gum infections, or other dental problems
  • taking other medications that can cause mouth or dental problems
  • dry mouth or dehydration
  • smoking
  • drinking alcohol
  • inadequate oral hygiene

What might help

If you have mouth ulcers during Nerlynx treatment, consider the following over-the-counter (OTC) or home remedy options to help relieve symptoms:

  • Gently brush your teeth with a mild toothpaste and soft toothbrush daily.
  • Avoid mouthwash that contains alcohol, which can be drying and irritating.
  • Rinse your mouth with a lukewarm saltwater solution.
  • Use OTC numbing gels, protective pastes, or moisturizing sprays.
  • Avoid foods that are acidic, spicy, or hard to chew.
  • Try to stop smoking (if you smoke).
  • Try to limit alcohol use (if you drink).
  • Drink plenty of water.

If you develop a fever or sore throat or have difficulty eating or drinking, check with your doctor right away. They may be able to prescribe medication to relieve the symptoms and promote healing.

Severe diarrhea

Severe diarrhea was a common side effect reported in studies of Nerlynx. Severe diarrhea may cause symptoms such as:

Factors that can increase the risk of severe diarrhea when taking this drug include:

What might help

To help prevent diarrhea, your doctor may prescribe loperamide (Imodium), which you’ll begin with your first dose of Nerlynx. If you still experience diarrhea while taking loperamide, your doctor may have recommendations. These include taking additional medications for diarrhea and electrolyte supplements.

It also may help to adjust your diet by eating bland foods, such as:

  • plain, boiled potatoes
  • plain oatmeal
  • dry toast
  • applesauce
  • plain white rice
  • bananas

If you have symptoms of severe diarrhea during Nerlynx treatment, keep drinking fluids. And be sure to talk with your doctor right away. They’ll likely recommend an urgent medical evaluation. Severe diarrhea can quickly lead to life threatening dehydration.

Liver problems

Liver problems were an uncommon side effect reported in studies of Nerlynx. Liver problems may cause symptoms such as:

  • fever
  • flu-like symptoms
  • lack of appetite
  • diarrhea
  • nausea and vomiting
  • dark urine
  • white or clay-colored stools
  • stomach pain
  • yellowing of your eyes and skin
  • itchy rash

Factors that can increase the risk of liver problems when taking this drug include:

  • having a history of liver problems
  • drinking excessive amounts of alcohol
  • taking other medications that can affect the liver

What might help

To help prevent liver problems during Nerlynx treatment, your doctor likely will measure levels of liver enzymes in your blood. This usually will occur:

  • before you start treatment
  • once monthly for the first 3 months of treatment
  • every 3 months thereafter

For liver problems that develop while taking Nerlynx, your doctor will determine the severity of damage. They may hold your dose until tests show that your liver enzyme levels have improved. Then, they’d restart your treatment at a lower dose and monitor your liver enzyme levels closely. Some people may have to stop Nerlynx completely if liver damage persists despite dose reductions.

Keeping track of side effects

During your Nerlynx 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 first start taking a new drug 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 your symptoms affected your daily activities
  • what other medications you were taking
  • any other information you feel is important

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

Below is important information you should consider before taking Nerlynx.

Warnings

Nerlynx can sometimes cause harmful effects in people who have certain conditions. This is known as a drug-condition interaction. Other factors also may affect whether Nerlynx is a good treatment option for you.

Talk with your doctor about your health history before you take Nerlynx. Be sure to tell them if any of the following factors apply to you:

  • liver problems
  • consume grapefruit or grapefruit-containing foods
  • take H2 blockers, antacids, or proton pump inhibitors
  • take other prescription medications, OTC drugs, herbs, vitamins, or nutritional supplements
  • past allergic reaction to Nerlynx
  • pregnancy
  • breastfeeding
  • consume alcohol

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.