If you have a type of cancer called multiple myeloma, your doctor might suggest Darzalex (daratumumab) as a treatment option for you. Along with other questions you may have about the drug, you could be wondering about its side effects.

Darzalex is a prescription medication that’s used to treat multiple myeloma in adults in certain situations. Depending on the situation, Darzalex may be used on its own or with other multiple myeloma treatments. And it may be given as short course or a long-term treatment.

Darzalex is a biologic drug (a drug made using living organisms). It’s a targeted therapy for cancer (a treatment that finds and attacks cancer cells). It’s also a form of immunotherapy (a treatment that helps your immune system attack cancer cells).

Darzalex comes in two forms, Darzalex and Darzalex Faspro.

  • A healthcare professional gives Darzalex by intravenous (IV) infusion in a doctor’s office or clinic. An IV infusion is an injection into a vein that’s given over a period of time. Infusions of Darzalex take 3 to 7 hours.
  • Darzalex Faspro contains an extra ingredient called hyaluronidase-fihj. A healthcare professional gives this form of Darzalex by subcutaneous injection. This is an injection under your skin, and it takes about 3 to 5 minutes.

This article focuses mainly on the side effects of Darzalex. To read about the differences in side effects between the two forms of Darzalex, see the “FAQs about Darzalex’s side effects” section below.

For more information about Darzalex, including details about how it’s used, see this in-depth article.

Like other drugs, Darzalex can cause mild or serious side effects, also known as adverse effects. Keep reading to learn more.

Some people may experience mild or serious side effects during their Darzalex treatment. Examples of Darzalex’s more commonly reported side effects include:

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

Other side effects from Darzalex are also possible. Read on to find out more.

Examples of mild side effects that have been reported with Darzalex 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, too. But if you have any symptoms that are ongoing or that bother you, talk with your doctor or pharmacist. And don’t stop using Darzalex unless your doctor recommends it.

Darzalex may cause mild side effects other than the ones listed above. See the Darzalex patient information for details.

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

Serious side effects that have been reported with Darzalex include:

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

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

Here are the answers to some frequently asked questions about Darzalex’s side effects.

How long do the side effects of Darzalex last?

Most mild side effects of Darzalex tend to lessen in a few days or a couple of weeks. If you have side effects that last longer or are troublesome, talk with your doctor.

Some serious side effects of Darzalex, such as infusion-related reactions, can decrease quickly with treatment. But others may last a long time, even with treatment. How long side effects last will depend on how they respond to any treatments you have for them.

If you have questions or concerns about how long Darzalex side effects may last, talk with your doctor.

How do the side effects of a Darzalex IV infusion compare with those of a Darzalex Faspro subcutaneous injection?

Darzalex is given by intravenous (IV) infusion, while Darzalex Faspro is given by subcutaneous injection. An IV infusion is an injection into a vein that’s given over a period of time. A subcutaneous injection is an injection given under your skin.

Both Darzalex and Darzalex Faspro can cause allergic reactions that happen during or shortly after the infusion or injection. These reactions are described in the “Side effects explained” section below.

Such allergic reactions are more common with Darzalex infusions than with Darzalex Faspro injections. But before you receive either form of Darzalex, you’ll be given medications to reduce your risk of having a reaction.

Darzalex Faspro can also cause mild skin reactions in the area where you have the injection. These can include redness or another change in skin color.

Are there other differences between the side effects that Darzalex and Darzalex Faspro can cause?

When Darzalex and Darzalex Faspro are used to treat multiple myeloma, they have very similar side effects. These are described above and below.

However, Darzalex Faspro is also used to treat another condition called light chain amyloidosis. When it’s used for this condition, Darzalex Faspro may cause serious or even fatal heart problems. Darzalex isn’t used for this condition, so it’s not known if it can cause this side effect.

For more information about how the side effects of Darzalex compare with those of Darzalex Faspro, talk with your doctor or pharmacist.

Can Darzalex cause cardiac problems?

Yes, Darzalex can sometimes cause cardiac (heart) problems when it’s used to treat multiple myeloma. In studies of Darzalex, a type of irregular heartbeat called atrial fibrillation (AFib) was reported in some people.

Symptoms of AFib can include:

If you have any of these symptoms, contact your doctor right away.

Learn more about some of the side effects that Darzalex may cause.

Infusion reaction

You’ll receive Darzalex as an intravenous (IV) infusion. An IV infusion is an injection into a vein that’s given over a period of time.

It’s possible to have a reaction to a Darzalex infusion. In fact, infusion reactions were one of the more common side effects reported in studies of Darzalex.

Infusion reactions are allergic reactions that happen during or shortly after an infusion of Darzalex. But it’s also possible to have a delayed reaction up to 3 days after the infusion.

Infusion reactions are usually mild or moderate, but they can be severe or life threatening. On rare occasions, they may even be fatal.

These reactions are most likely to happen with the first dose of Darzalex. You’re much less likely to have this side effect with subsequent doses.

Darzalex infusion reactions can cause symptoms such as:

What might help

Before each infusion of Darzalex, you’ll receive medications to reduce your risk of infusion reactions. You’ll usually be given a combination of:

You’ll also be given corticosteroids the day after your Darzalex infusion to reduce your risk of delayed reactions.

To lower your risk of infusion reactions, your first infusion will typically be given over about 7 hours. But after this, your infusions can usually be given over 3 to 5 hours.

A healthcare professional will monitor you closely during each infusion. If you have a mild or moderate reaction, they may pause your infusion to treat your symptoms. After your symptoms have gone away, they’ll restart the infusion at a slower rate. This is so you get the medication more slowly.

If you have a severe or life threatening reaction, your doctor may permanently stop your Darzalex treatment.

If you have a delayed reaction after leaving your doctor’s office or the infusion center, call your doctor right away. But if you have symptoms that feel life threatening or you think you’re having a medical emergency, call 911 right away.

Low blood cell counts

Like many cancer treatments, Darzalex commonly causes low blood cell counts. So you may have low levels of white blood cells, red blood cells, or platelets while you have treatment with Darzalex.

A low level of neutrophils (a type of white blood cell) is called neutropenia. White blood cells help your body fight germs that can cause infections. If you have neutropenia with Darzalex, you may have an increased risk of infections. Symptoms of infections can include:

A low level of red blood cells is called anemia. Red blood cells carry oxygen throughout your body. If you have anemia with Darzalex, you may have symptoms such as:

A low level of platelets is called thrombocytopenia. Platelets help your blood clot after an injury. If you have thrombocytopenia with Darzalex, you may have symptoms such as:

  • bruising easily
  • bleeding, such as nosebleeds or bleeding gums
  • taking longer than usual to stop bleeding

What might help

Your doctor will check your blood cells frequently while you have Darzalex. During or after the treatment, tell your doctor right away if you have symptoms of low blood cell counts.

If you have low blood cell counts, your doctor may delay your next Darzalex infusion until your blood cell levels recover.

Respiratory infections

You may get respiratory infections while you’re having treatment with Darzalex. In fact, upper respiratory infections, such as colds, were commonly reported in studies of the drug.

Respiratory infections are typically mild, but they can sometimes become more serious and affect your lungs. Serious infections, such as the flu, bronchitis, and pneumonia, have been reported in people taking Darzalex.

Symptoms of serious respiratory infections may include:

  • cough
  • coughing up blood or phlegm
  • shortness of breath
  • chest pain
  • fever
  • shivering
  • extreme lack of energy

What might help

You can help protect yourself from respiratory infections while you’re having Darzalex treatment by:

Before you start receiving Darzalex, talk with your doctor about getting vaccines, such as the flu shot, COVID-19 vaccine, or pneumonia vaccine.

If you get a mild respiratory infection, such as a cold, during your treatment, talk with your doctor or pharmacist. If your symptoms are troublesome, they can recommend over-the-counter treatments that are suitable for you.

But if the infection doesn’t get better after a few days or your symptoms start to get worse, see your doctor. You may need medication to treat the infection and stop it from getting worse.

If you have symptoms of a serious respiratory infection, contact your doctor right away. You’ll need medication to treat the infection.

Peripheral sensory neuropathy

Darzalex can sometimes cause a side effect called peripheral sensory neuropathy. This is nerve damage that causes tingling or burning sensations, numbness, or pain in your hands or feet.

In studies of Darzalex, peripheral sensory neuropathy was one of the more commonly reported side effects.

What might help

If you have symptoms of peripheral sensory neuropathy while you’re having Darzalex treatment, talk with your doctor. They can suggest ways to help manage this side effect.

For example, if you have troublesome pain in your hands or feet, your doctor may prescribe medication to help with this. They may suggest a numbing cream or patch to put directly on the area where you’re having pain. Or they may prescribe certain antidepressants or seizure medications that are also used for nerve pain.

Other treatments that may be helpful for this nerve problem include physical therapy, acupuncture, and electrical nerve stimulation. Your doctor can tell you more about these treatments.

Here are some other tips to help manage this side effect:

  • Hot and cold temperatures can sometimes make neuropathy worse. If this is the case for you, avoid taking hot baths or showers. You may also want to keep your hands and feet covered and warm in cold temperatures.
  • If you have numbness, this can lead to injuries. Take care of your hands and feet, and check them often to make sure you don’t have any sore or damaged areas.
  • If the neuropathy is in your feet, always wear shoes that protect your whole foot, even when you’re at home. And make sure that your shoes aren’t too tight.
  • If the neuropathy is in your hands, take extra care when using sharp objects, such as knives or scissors.

Allergic reaction

Like most drugs, Darzalex can cause an allergic reaction in some people.

The 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 might help

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

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

Keeping track of side effects

During your Darzalex treatment, consider keeping notes about 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 things such as:

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

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

Darzalex may not be right for you if you have certain medical conditions or other factors that affect your health. Talk with your doctor about your health history before you start the treatment. The list below includes factors to consider.

History of hepatitis B. If you’ve had hepatitis B in the past, Darzalex could make this infection active again in your body. Before you start Darzalex treatment, your doctor will test you for the hepatitis B virus (HBV). If you test positive, your doctor will check for signs of HBV becoming active during and after your Darzalex treatment.

History of chickenpox or shingles. Chickenpox and shingles are caused by the herpes zoster virus. If you’ve had either infection in the past, Darzalex could make the virus flare up in your body. This can cause shingles. If you’ve had chickenpox or shingles, your doctor may prescribe antiviral medication to prevent shingles while you have Darzalex.

Allergic reaction. If you’ve had an allergic reaction to Darzalex or any of its ingredients, you shouldn’t have this treatment. Ask your doctor what other medications are better options for you.

Chronic obstructive pulmonary disease (COPD). COPD is a long-term lung condition that causes breathing problems. If you have COPD, you may need extra medications to help your breathing. Your doctor may prescribe extra inhalers to open your airways or corticosteroids to reduce swelling in your lungs.

Alcohol use and Darzalex

Alcohol isn’t known to interact with Darzalex. But it’s recommended that you avoid drinking alcohol the day before and after your infusions. That’s because alcohol can make you dehydrated. It’s important to stay hydrated before, during, and after your infusions. This is because Darzalex can cause dehydration as well.

Alcohol might also increase your risk of certain side effects that you may have with Darzalex. These include nausea, diarrhea, or tiredness.

If you have questions about drinking alcohol while you’re having Darzalex treatment, talk with your doctor.

Pregnancy and breastfeeding while taking Darzalex

Darzalex can harm a developing fetus, so it isn’t safe to take during pregnancy. If you’re pregnant or plan to become pregnant, be sure to tell your doctor before you start Darzalex treatment.

If you’re able to become pregnant, it’s recommended that you use birth control during the treatment. You’ll need to continue using birth control for 3 months after your last dose of the drug.

It’s not known if Darzalex can pass into breast milk. But it’s not recommended that you breastfeed while having this treatment. If you’re breastfeeding or planning to breastfeed, talk with your doctor about the best way to feed your baby while taking Darzalex.

Like many cancer treatments, Darzalex can cause side effects. Most of these are mild and easily managed, but serious side effects are also possible. Your doctor will carefully monitor you for these side effects during your treatment so that they can detect and treat any early.

If you’d like to know more about possible side effects of Darzalex, talk with your doctor. They can help you decide if this medication is a good option for you.

Examples of questions you might ask include:

  • Is it safe to use Darzalex if I have asthma?
  • Are side effects more common if Darzalex is used with other medications?
  • Will I need any monitoring for side effects?
  • Does Darzalex increase my risk of getting COVID-19?

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.