Side Effects of Keytruda: Examples and Treatment

Some people may experience mild or serious side effects during their Keytruda treatment. These side effects can vary depending on whether Keytruda is used alone or with other cancer drugs.

Examples of Keytruda’s commonly reported side effects include:

• diarrhea
• fatigue (lack of energy)
• loss of appetite
• nausea
• itchy skin or rash*

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

Read on to learn about other possible side effects of Keytruda.

Keytruda may cause mild side effects. These side effects can vary depending on whether Keytruda is used alone or with other cancer drugs.

Examples of mild side effects that have been reported with Keytruda include:

• belly pain
• constipation
• cough
• diarrhea
• fatigue (lack of energy)
• fever
• loss of appetite
• nausea
• shortness of breath
• muscle or bone pain*
• hair loss*
• itchy skin or rash*

* To learn more about this side effect, see “Side effects explained” 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 Keytruda unless your doctor tells you to.

Keytruda may cause mild side effects other than the ones listed above. See the Keytruda prescribing information for more 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 Keytruda, visit MedWatch.

Serious side effects may occur with Keytruda. These side effects can vary depending on whether Keytruda is used alone or with other cancer drugs.

Many of Keytruda’s serious side effects happen because of an overactive immune system. These are called immune-mediated side effects, and they often cause inflammation (damage and swelling) to tissues. Examples include:

• adrenal insufficiency
• arthritis
• colitis, which affects the colon
• encephalitis, a condition of the brain
• hepatitis or liver damage
• myasthenia gravis, which affects the muscles
• nephritis, which affects the kidneys
• pancreatitis, which involves the pancreas
• pneumonitis, which is different from pneumonia, though both affect the lungs
• uveitis, a condition that can affect one or both eyes
• blood sugar level problems, including type 1 diabetes and diabetic ketoacidosis
• severe skin reactions, including Stevens-Johnson syndrome and toxic epidermal necrolysis
• hormone problems, which can include:
  • hypothyroidism
  • hyperthyroidism
  • thyroiditis
  • hypophysitis
• other side effects related to overactivity of the immune system, which can affect your:
  • heart
  • nervous system
  • eyes
  • stomach or intestines
  • muscles
  • blood cells

Other serious side effects that have been reported with Keytruda include:

• allergic reaction*
• infusion-related reactions (a strong immune system response that can happen during or shortly after your Keytruda infusion)

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

If you develop serious side effects while using Keytruda, 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.

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

Does Keytruda cause any long-term side effects?

In most cases, Keytruda’s side effects should be temporary. Most should go away soon after you start or stop the drug.

But Keytruda can cause serious side effects that may lead to long-term problems. In some cases, these problems can take many weeks or months to resolve. Here are some examples, all of which cause inflammation (damage and swelling) in different parts of the body:

These are not all the long-term side effects that Keytruda may cause. If you have questions about what to expect long term while using Keytruda, talk with your doctor or pharmacist. But don’t stop your Keytruda treatment unless your doctor recommends it.

Could I experience any eye problems while using Keytruda?

Yes, in rare cases, Keytruda may cause serious eye side effects (sometimes called ocular side effects).

Examples of eye problems that may happen while using Keytruda include:

• blindness
• retinal detachment (separation of the retina from the back of the eye)
• uveitis (inflammation of the middle layer of the eye)

Symptoms of eye side effects from Keytruda will depend on the exact eye problem you have. But possible symptoms that may happen with one or both eyes include:

• blurry vision
• eye floaters
• eye pain
• eye redness
• sensitivity to light

Tell your doctor right away if you have any symptoms of eye problems while using Keytruda.

What are Keytruda’s side effects when it’s used to treat lung cancer?

Keytruda is prescribed to treat many types of cancer, including non-small cell lung cancer and small cell lung cancer. The side effects of Keytruda are expected to be the same regardless of the type of cancer it’s treating.

However, Keytruda may be prescribed by itself or with other drugs for lung cancer, such as chemotherapy drugs. This can affect the side effects you experience.

In addition to the side effects Keytruda may cause when given alone, the following side effects also occurredwhen Keytruda was given with chemotherapy in studies:

• headache
• peripheral neuropathy (numbness or tingling in your hands or feet)
• mouth sores
• insomnia
• joint pain

For a full list of the cancers Keytruda is used to treat, see this in-depth article on the drug.

To learn more about possible side effects of Keytruda, see the “What are the mild side effects of Keytruda?” and “What are the serious side effects of Keytruda?” sections above.

If you have questions about what to expect when using Keytruda to treat lung cancer, talk with your doctor.

Is confusion a side effect of Keytruda?

Yes, confusion is a possible side effect of Keytruda. In fact, confusion was a common side effect of Keytruda in studies of the drug.

Confusion can make you feel as though you can’t think clearly. You may also have problems making decisions or focusing on a task. This side effect can also lead to abnormal or slurred speech.

It’s important to remember that encephalitis (inflammation of your brain) may cause confusion. Encephalitis is a rare but serious side effect of Keytruda. For this reason, you should tell your doctor right away if you experience confusion while using Keytruda. They’ll likely check you for signs of encephalitis.

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

Muscle or bone pain

Muscle pain or bone pain are common side effects of Keytruda.

What might help

You can relieve muscle or bone pain by:

• applying ice to the painful area
• resting the painful area
• stretching the affected muscle
• taking over-the-counter (OTC) pain relievers, such as acetaminophen (Tylenol) and ibuprofen (Advil, Motrin)

Before using OTC drugs with Keytruda, talk with your doctor or pharmacist. And ask your doctor about other ways to relieve bothersome muscle or bone pain that Keytruda may cause.

Hair loss

In rare cases, some people may have hair loss while using Keytruda. In studies, hair loss was more common when Keytruda was used with chemotherapy drugs than when used alone.

What might help

Hair loss as a side effect of Keytruda is usually temporary. If you have hair loss from using Keytruda, your hair should start growing back several weeks after your last dose.

Cooling caps, which are caps designed to keep your scalp cold, might help prevent hair loss. Cooling caps lessen the blood flow to your scalp, which may decrease the effect of Keytruda or chemotherapy on your hair. Ask your doctor if a cooling cap is right for you.

When your hair does start to return, don’t overuse hair styling tools that are harsh on hair. These include blow dryers and hair straighteners. You should also avoid bleaching or coloring your hair so it stays healthy enough to grow.

If you experience bothersome hair loss while using Keytruda, talk with your doctor about ways to help with this side effect.

Itchy skin or rash

You may have itchy skin or rash from using Keytruda. Itchy skin and mild rashes are common side effects of the drug.

In rare cases, Keytruda may also cause severe rashes and other skin reactions. These include Stevens-Johnson syndrome (SJS) and toxic epidermal necrolysis (TEN). With SJS and TEN, you have a rash along with painful sores on your eyes, genitals, mouth, or throat. These reactions are potentially life threatening and require immediate medical attention.

What might help

Here are a few tips for helping relieve mild itching and rash:

• Avoid showering or bathing in hot water. Instead, bathe in cool water with oatmeal or baking soda.
• Avoid scratching, as this can worsen the itch and irritate the rash.
• Keep your skin hydrated with a moisturizer.
• Use over-the-counter antihistamines, such as diphenhydramine (Benadryl), or a steroid cream, such as hydrocortisone cream. But be sure to check with your doctor or pharmacist before using other drugs with Keytruda.

If you have a severe skin reaction to Keytruda, you’ll likely need treatment in a hospital. If you have severe skin peeling or blisters after using the drug, call 911 or your local emergency number right away. These may be signs of a serious skin reaction, which can be life threatening.

If you’re concerned about your risk for a severe skin reaction from using Keytruda, talk with your doctor.

Allergic reaction

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

Symptoms can be mild or serious and can include:

• 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. They may suggest an over-the-counter antihistamine you can take by mouth, such as diphenhydramine (Benadryl), or a product you can apply to your skin, such as hydrocortisone cream, to manage your symptoms.

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

Keeping track of side effects

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

Your side effect notes can include things like:

• what dose of drug you received 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 Keytruda affects you. And your doctor can use this information to adjust your treatment plan if needed.

Keytruda is used to treat certain types of cancer in some children. (For information about the cancers Keytruda can treat in children, see this detailed article on the drug.)

Most side effects that occur in children receiving Keytruda are similar to those that adults experience. However, some side effects of Keytruda are more common in children. These include:

• fever
• headache
• low levels of red blood cells and white blood cells
• upper respiratory infection, such as the common cold
• vomiting

Talk with your child’s doctor about their risk for side effects from Keytruda.

Keytruda 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 take Keytruda. Factors to consider include those in the list below.

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

Receiving certain other treatments for multiple myeloma. Using Keytruda with certain other treatments for multiple myeloma can be fatal. (Multiple myeloma is a cancer that affects a type of white blood cell called a plasma cell.) Before using Keytruda, tell your doctor if you’re taking any treatments for multiple myeloma.

Received an organ transplant. Before using Keytruda, tell your doctor if you’ve had an organ transplant. Keytruda can raise the risk for your immune system attacking the transplanted organ. If you’ve had a transplant, your doctor will tell you what symptoms of organ rejection you should watch for while using Keytruda.

Received or plan to receive a stem cell transplant. Before using Keytruda, tell your doctor if you’ve received stem cells from a donor in the past or plan to do so. You may be at a higher risk for graft-versus-host disease. This condition causes your immune system to attack the transplant stem cells. Talk with your doctor about whether Keytruda is safe for you to use.

Alcohol and Keytruda

It should be safe to drink alcohol while using Keytruda.

But be aware that alcohol can cause side effects that are similar to some of Keytruda’s. These include diarrhea, fatigue (lack of energy), and nausea. If you drink alcohol during Keytruda treatment, it may make these side effects worse.

If you drink alcohol, talk with your doctor about the amount that’s safe for you to drink while using Keytruda.

Pregnancy and breastfeeding while taking Keytruda

You shouldn’t use Keytruda while pregnant or breastfeeding.

Keytruda hasn’t been studied during pregnancy. But based on how the drug works, Keytruda may cause harm to infants born to pregnant females* who used the drug during pregnancy.

For this reason, you should use birth control while taking Keytruda if you or your partner can become pregnant. And you should continue to use birth control for at least 4 months after your last dose.

It isn’t known if Keytruda can pass into breast milk. To be safe, you shouldn’t breastfeed while using Keytruda and for at least 4 months after your last dose.

Before starting Keytruda treatment, tell your doctor if you’re pregnant or planning to become pregnant. Also tell them if you’re breastfeeding or planning to breastfeed. They can discuss your options with you.

* In this article, we use the term “female” to refer to someone’s sex assigned at birth. For information about the difference between sex and gender, see this article.

Keytruda is a drug used to treat certain types of cancer in adults and some children.

Some people who use Keytruda may have mild side effects. Although rare, serious side effects can occur with Keytruda. Many of these happen because of an overactive immune system. Keep in mind that the side effects of Keytruda can vary depending on whether Keytruda is used alone or with other cancer drugs.

Talk with your doctor or pharmacist if you have questions about Keytruda’s side effects. Here are a few questions you may want to ask:

• Can you recommend treatment for side effects I’m experiencing with Keytruda?
• Are there any side effects of Keytruda that I should tell you about right away?
• If I’ve had an organ transplant, what symptoms of organ rejection should I watch for while using Keytruda?

To learn more about Keytruda, see these articles:

• All About Keytruda
• Imfinzi vs. Keytruda: What You Should Know
• Keytruda and Cost: What You Need to Know

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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.