Key takeaways

  • Enhertu, which is used to treat certain cancers, has common side effects, including hair loss and nausea. These can often be managed with your doctor’s guidance.
  • Your doctor will monitor for and treat potential serious Enhertu side effects, which can include heart and lung problems. If you have an existing lung problem, your doctor may recommend a different treatment instead.
  • Enhertu is not safe to use during pregnancy due to the risk of fetal harm. You may need to use birth control during and after treatment.

Enhertu (fam-trastuzumab deruxtecan-nxki) is used in certain situations to treat the following kinds of cancer in adults:

As with other cancer drugs, Enhertu has a number of potential side effects ranging from mild to serious.

Enhertu also has boxed warnings for interstitial lung disease, pneumonitis, and risk of fetal harm if used during pregnancy. A boxed warning is the most serious warning from the Food and Drug Administration (FDA). For details, see the “Boxed warnings for Enhertu” section.

Enhertu can cause mild side effects, some more common than others, and side effects from Enhertu can vary depending on the condition it is being used to treat.

Mild side effects reported in clinical studies of Enhertu included:

  • fever
  • fatigue
  • decreased appetite
  • vomiting
  • constipation
  • nausea
  • diarrhea
  • hair loss

This list does not include all mild and more common side effects of Enhertu. For more details see Enhertu’s prescribing information.

These side effects should mostly be temporary, and some may be easily manageable. But if you have any symptoms that are ongoing or bother you, talk with your doctor or pharmacist. Do not stop Enhertu treatment unless your doctor recommends it.

For more information about some of the mild and more common Enhertu side effects listed above, see the “Side effect specifics” section.

Serious side effects that have been reported in studies of Enhertu include:

This list does not include all potentially serious side effects of Enhertu. For more details see Enhertu’s prescribing information.

If you develop serious side effects while taking Enhertu, 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 your local emergency number.

For more information about some of the serious Enhertu side effects listed above, see the “Side effect specifics” and “Boxed warnings for Enhertu” sections.

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

Hair loss

You may have hair loss during treatment with Enhertu. This was a common side effect reported in studies of people receiving this medication. Hair loss can occur not only on your head but also on other areas of your body where hair grows. For example, it can affect your eyelashes, eyebrows, or hair on your legs and arms.

What you can do

To help with hair loss, avoid harsh products such as hairsprays or dyes and use a mild shampoo.

Scalp cooling may also help prevent hair loss. This type of treatment works by inhibiting blood flow to your scalp, which helps limit the amount of Enhertu that reaches the hair follicles there. Scalp cooling treatment starts before you receive an Enhertu infusion and continues for a few hours afterward. Your doctor can tell you more about options for scalp cooling.

If you’re concerned about hair loss while receiving Enhertu, talk with your doctor. They may have other suggestions for treating this side effect.

Nausea

You may have nausea from receiving Enhertu. This was the most common side effect reported in studies of the drug.

What you can do

If you develop nausea during Enhertu treatment, there are a few things you can try to reduce this side effect. Eating smaller meals more often may help decrease nausea. So instead of having three large meals each day, try eating six small meals or snacks.

In addition, consider avoiding foods that are very hot or cold or have strong smells. Sometimes, it’s best to eat bland foods.

If you’re still having nausea, your doctor may be able to prescribe a medication to help relieve this side effect. Talk with your doctor about the best ways to treat nausea while you’re receiving Enhertu.

Heart problems

Though rare, it’s possible to develop heart problems from receiving Enhertu. Heart problems from Enhertu may affect the left side of your heart. This, in turn, can affect your heart’s ability to pump blood throughout your body.

What you can do

Before you start receiving Enhertu, your doctor will likely test your heart to be sure it’s healthy enough for treatment. During treatment, your doctor will monitor you for symptoms of heart conditions, such as swelling of the arms or legs or difficulty breathing. In addition, your doctor may test your heart throughout treatment to monitor your heart function.

If your heart function worsens during treatment, your doctor may recommend pausing treatment, decreasing your dose, or stopping treatment altogether. If you have a history of heart disease or other heart conditions, your doctor may recommend a different treatment option for you.

If you have questions about the heart problems Enhertu may cause, talk with your doctor.

Allergic reaction

Like most drugs, Enhertu can cause an allergic reaction in some people. But it’s not clear whether this side effect occurred in studies.

Symptoms can be mild or serious and can include:

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

What you can do

If you have mild symptoms of an allergic reaction, such as a mild rash, call your doctor right away. They may suggest an over-the-counter antihistamine you take by mouth, such as diphenhydramine (Benadryl), to manage your symptoms. Or they may recommend a product you apply to your skin, such as hydrocortisone cream.

If your doctor confirms you had a mild allergic reaction to Enhertu, they’ll decide whether you should continue receiving it.

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.

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

Enhertu has boxed warnings. A boxed warning is the most serious warning from the FDA. It alerts doctors and patients about drug effects that may be dangerous.

Risk of serious lung problems

Enhertu has a boxed warning about the risk of serious lung problems. Rarely, Enhertu can cause interstitial lung disease (ILD) and pneumonitis, which cause inflammation in the lungs that can lead to scarring of lung tissue, making it harder for you to breathe. It’s important to be aware of the symptoms of ILD so that you can receive treatment right away. Symptoms may include:

What you can do

Throughout Enhertu treatment, your doctor will monitor you for ILD by ordering blood work and other tests, such as a CT scan. This can help identify and manage ILD as soon as possible.

If you develop new or worsened symptoms of a lung problem, contact your doctor right away. Sometimes, they may recommend pausing your treatment or reducing your dose of Enhertu. Your doctor may also suggest taking a steroid medication, such as prednisone (Rayos), to reduce your symptoms.

Depending on the severity of your symptoms, your doctor may recommend that you stop receiving Enhertu and try a different treatment for your cancer.

This medication can worsen existing lung problems. If you have a condition that affects your breathing, such as asthma, be sure to tell your doctor before starting Enhertu. Your doctor may recommend a different treatment option for you.

If you have more questions or concerns about lung problems during Enhertu treatment, talk with your doctor.

Risk of fetal harm

Enhertu also has a boxed warning for the risk of fetal harm. For this reason, Enhertu should not be used during pregnancy.

Enhertu can cause harm to a fetus, including skeletal or lung development problems. It may even be life threatening to a newborn. Due to these risks, if you can become pregnant, your doctor will likely give you a pregnancy test before you start treatment.

What you can do

If you are sexually active and can become pregnant, use birth control during treatment with Enhertu and for 7 months after stopping treatment. Males with partners who can become pregnant should use birth control throughout treatment and for 4 months afterward.

If you become pregnant at any time during Enhertu treatment, tell your doctor right away. And if you have any questions about Enhertu and pregnancy, talk with your doctor.

Note: In this article, we use the terms “male” and “female” to refer to someone’s sex assigned at birth. Here’s more information about the difference between sex and gender.

Keeping track of side effects

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

Your side effect notes can include:

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

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

It varies depending on the side effect as well as the person.

Mild side effects, such as nausea or diarrhea, may go away within a few days to a couple of weeks as your body gets used to Enhertu.

But some of Enhertu’s side effects may be long term or even permanent, though these tend to be rare. Examples include serious heart and lung problems. (Enhertu has a boxed warning for the risk of serious lung problems. For details, see the “Boxed warnings for Enhertu” section.)

Before you start Enhertu treatment, your doctor will determine your risk of serious side effects. This includes going over your health history and possibly having you get certain lab tests. To help prevent any side effects you may have a risk of, your doctor may:

  • decrease your dose
  • slow the rate of the infusion (you receive Enhertu as an intravenous infusion)
  • provide you with nausea medications, steroids, or both before starting Enhertu

If your risk of a serious Enhertu side effect is high, your doctor may recommend you try a different treatment for your cancer.

Throughout treatment, your doctor will monitor you for the possibility of Enhertu toxicity (harm caused by Enhertu). Although many of Enhertu’s side effects are mild, the drug can cause some severe side effects. Sometimes, side effects become so severe that a person needs to stop Enhertu treatment. This is known as “unacceptable toxicity.”

For example, if you develop lung problems from Enhertu, your doctor may recommend pausing your treatment or decreasing your dose. (To learn more, see the “Boxed warnings for Enhertu” section.)

If these lung problems linger or worsen, this may be considered an unacceptable toxicity. In other words, Enhertu may be harmful to your health.

If you develop an unacceptable toxicity from Enhertu, your doctor will likely recommend that you stop Enhertu treatment. They may suggest a different treatment for your cancer.

During treatment with Enhertu, your doctor will monitor you for any potential side effects.

For instance, they’ll monitor your blood for low levels of red blood cells, white blood cells, and platelets. Your doctor will check to make sure that these levels don’t become too low, which can increase your risk of infection. If your blood cell levels get too low during Enhertu treatment, your doctor may decrease your dose or pause your treatment.

In addition, Enhertu can cause heart problems. Before you start receiving this medication, you’ll have tests to see how well your heart is functioning. And you’ll have these tests throughout treatment to monitor your heart function. Depending on the results, your doctor may recommend a pause in Enhertu treatment or a decrease in the dose.

To lower your risk of serious side effects, it’s important to have the tests that your doctor recommends. This can help identify side effects as soon as possible so you can receive treatment before they become serious.

You can monitor yourself for side effects during Enhertu treatment. For example, if you develop a cough or fever after receiving Enhertu, tell your doctor right away. This may be a symptom of lung problems, which require immediate treatment.

For more ways to decrease your risk of serious side effects during Enhertu treatment, talk with your doctor.

Before starting Enhertu, discuss your health history with your doctor. Enhertu may not be right for you if you have certain medical conditions or other factors that affect your health. Be sure to talk with your doctor if any of the following apply to you:

  • heart problems
  • lung problems
  • a previous allergic reaction to Enhertu or any of its ingredients
  • an active infection
  • alcohol consumption
  • pregnancy and breastfeeding

Enhertu is a medicine used to treat certain types of cancer by targeting specific cells. It can cause several side effects. Most people with Enhertu side effects experience mild issues like feeling very tired, nausea, vomiting, or losing some hair. It can also cause stomach problems like constipation or a loss of appetite. However, there are more serious risks to watch for, such as dangerous lung inflammation or heart problems that make it hard to breathe. Because Enhertu can lower your white blood cell count, it might also be harder for your body to fight off infections. Doctors monitor patients closely for these symptoms and advise that the drug is not safe to use during pregnancy.

Disclaimer: While Healthline strives for factual, comprehensive, and current information, this article is not a substitute for a licensed healthcare professional’s expertise. Always consult a doctor before taking or discontinuing any medication. Drug information is subject to change and may not cover all uses, directions, precautions, warnings, interactions, reactions, or adverse effects. The lack of a warning does not guarantee a drug’s safety, effectiveness, or appropriateness for all patients or specific uses. Learn more about our approach to content integrity.