Keytruda's Side Effects: What to Know

Medically Reviewed By Melissa Badowski, PharmD, MPH, FCCP

Keytruda: Introduction

Keytruda is a brand-name prescription drug. It’s a type of medication called an immunotherapy drug. Specifically, it’s a programmed death receptor-1 (PD-1) inhibitor. Keytruda contains the active drug pembrolizumab. It comes as a solution and is given by IV infusion.  

Keytruda is approved by the Food and Drug Administration (FDA) to treat different types of advanced cancers in adults and some children. It may be used to treat lung cancer, melanoma, lymphoma, and other types of cancers.

For a general overview of Keytruda, including details about its uses, see this article.

Similar to other drugs, Keytruda may cause side effects. Read below for information about possible side effects, including common, mild, and serious ones.

If you’d like to take Keytruda, search here to find a healthcare professional who might prescribe it.

Keytruda: More common side effects

Some of Keytruda’s side effects may be more common than others. These side effects may last a few days or weeks. However, some side effects may last longer or become severe or bothersome. Tell your doctor or pharmacist if you have concerns about any side effects with Keytruda.

Some of the more common side effects of Keytruda that occurred during clinical studies are listed below. These side effects can vary depending on the condition it is being used to treat.

More common side effects of Keytruda in people with melanoma include:

  • diarrhea
  • fatigue
  • itchy skin
  • constipation
  • skin rash*

More common side effects of Keytruda in people with lung cancer include:

More common side effects of Keytruda in people with head and neck cancer include:

  • fatigue
  • constipation
  • diarrhea
  • skin rash*
  • hypothyroidism (low thyroid hormone level)*

More common side effects of Keytruda in people with lymphoma include:

  • infection of the nose, sinuses, or throat
  • muscle and joint pain
  • fatigue
  • fever
  • cough

More common side effects of Keytruda in people with bladder cancer include:

  • fatigue
  • muscle and joint pain
  • low appetite
  • constipation
  • itchy skin

More common side effects of Keytruda in people with cervical cancer include:

  • fatigue
  • muscle and joint pain
  • diarrhea
  • abdominal pain

More common side effects of Keytruda in people with kidney cancer include:

  • muscle and joint pain
  • fatigue
  • diarrhea
  • itchy skin
  • hypothyroidism (low thyroid hormone level)*

More common side effects of Keytruda in people with solid tumors include:

  • muscle and joint pain
  • fatigue
  • diarrhea
  • itchy skin
  • hypothyroidism (low thyroid hormone level)*

* For more information about this side effect, see “Keytruda: Side effects explained” below.

Keytruda: Mild side effects

Keytruda can cause mild side effects, which are listed below. However, this list doesn’t include all possible mild side effects. To learn more about Keytruda’s side effects, view the drug’s prescribing information.

Keytruda’s mild side effects include:

The side effects listed above may last only a few days to weeks. However, some side effects may last longer or become severe or bothersome. Tell your doctor or pharmacist if you have concerns about side effects with Keytruda.

Note: After the Food and Drug Administration (FDA) approves a drug, it tracks side effects of the medication. If you develop a side effect while taking Keytruda and want to tell the FDA about it, visit MedWatch.

* For more information about this side effect, see “Keytruda: Side effects explained” below.

Keytruda: Serious side effects

It’s possible to have serious side effects with Keytruda. Serious side effects are listed below, but this list may not include all possibilities. To learn more about Keytruda’s side effects, view the drug’s prescribing information.

Call your doctor right away if you have serious side effects with Keytruda. However, if you think you’re having a medical emergency or have life threatening side effects, call 911 or your local emergency number.

Serious side effects of Keytruda and their possible symptoms include:

  • Pneumonitis (inflammation of the lungs). Symptoms can include:
  • Colitis (inflammation of the large intestine). Symptoms can include:
    • diarrhea
    • abdominal pain
    • blood in your stool
  • Hormone disorders such as hypophysitis (inflammation of the pituitary gland). Symptoms can include:
    • headache
    • photophobia (eye pain caused by bright lights)
    • trouble seeing
  • Nephritis (inflammation of the kidneys). Symptoms can include:
  • Serious skin rash. Symptoms can include:
    • blistering
    • skin peeling
  • Confusion.
  • Hypothyroidism (low thyroid hormone level).*
  • Hepatitis and liver damage.*
  • Infusion reactions.*
  • Severe allergic reaction.*

* For more information about this side effect, see “Keytruda: Side effects explained” below.

Keytruda: Side effects in children

Keytruda is approved to treat certain types of cancer in some children. Many side effects of Keytruda are expected to be the same in children and adults. However, certain side effects of Keytruda may be more common in children than in adults. Examples of these may include:

  • fever
  • vomiting
  • infection of the nose, sinuses, or throat
  • headache

If you have questions about your child’s side effects of Keytruda, talk with their doctor.

Keytruda: Common questions about side effects

Here are some common questions about Keytruda’s side effects and their answers. Talk with your doctor if you have other questions about this drug.

Is confusion a side effect of Keytruda?

Yes, confusion can occur with Keytruda. However, it isn’t a common side effect.

In one clinical study of people with head and neck cancer, confusion was a reported serious side effect. In this study, confusion was a side effect that led to stopping treatment with Keytruda.

Changes in mental state were also a reported side effect in another clinical study. This study included people receiving Keytruda for lymphoma.

If you have questions about confusion with Keytruda, talk with your doctor.

Are eye side effects possible with Keytruda?

Yes, Keytruda may cause different types of eye side effects.

A serious side effect of Keytruda is called immune-mediated adverse reactions. These are side effects that occur because of an overactive immune system. When the immune system is overactive, it can cause inflammation in different parts of the body, such as the kidneys, colon, and eyes.

For example, uveitis and iritis are two eye disorders caused by inflammation in different parts of the eye. Without treatment, inflammation in the eye can cause complications such as vision loss.

Some people may develop hypophysitis with Keytruda. Hypophysitis is an inflammation of the pituitary gland in the brain. With hypophysitis, some people may have changes in their vision, including partial blindness.

If you have questions about eye side effects of Keytruda, talk with your doctor.

Will using Keytruda in combination with Inlyta cause specific side effects?

Yes, taking Keytruda with the cancer medication Inlyta can cause specific side effects. Inlyta contains the active drug axitinib. It belongs to a drug class called kinase inhibitors.

Receiving Keytruda in combination with Inlyta may cause the following specific side effects:

People with hand-foot syndrome have redness, swelling, and pain on the palms of their hands or feet. Some people may develop blisters.

Dysphonia is a side effect that can change your voice. Your voice may become more hoarse than usual.

If you have questions about the side effects of using Keytruda with Inlyta, talk with your doctor.

Does Keytruda cause certain side effects when it is used for lung cancer?

Yes, Keytruda causes certain side effects when it’s used for treating lung cancer. Sometimes people with lung cancer need to combine Keytruda with chemotherapy. This can cause additional side effects.

Typically, people may experience different side effects when receiving Keytruda for lung cancer than for other cancers. However, people receiving Keytruda for lung cancer may have similar side effects to people receiving it for head and neck cancer or lymphoma.

The following side effects of Keytruda are seen in people with lung cancer:

These specific side effects sometimes lead to stopping treatment or adjusting your dosage of Keytruda. If you have questions about what side effects to expect with Keytruda, talk with your doctor.

Can Keytruda’s 6-week dosing schedule cause different side effects than its other dosing schedules?

It’s unlikely. When receiving Keytruda every 6 weeks, your doctor injects a higher dose compared with the dose given every 3 weeks. However, the expected side effects of Keytruda are the same regardless of the dosing schedule.

Doctors can prescribe Keytruda every 6 weeks based on how well your cancer responds to treatment. If you have bothersome side effects or your cancer isn’t improving, your doctor may change your dose of Keytruda.

Keytruda: Side effects explained

Here’s detailed information about some of Keytruda’s side effects.

Infusion reactions

Infusion reactions may occur in some people who receive IV infusions of medications. These side effects from the infusion can sometimes be severe or life threatening. To find out how often these reactions occurred with Keytruda, see the prescribing information.

Reactions may include:

Doctors rate the severity of infusion reactions by grade. Mild reactions are considered grade 1 and life threatening reactions are grade 4.

What to do

Your doctor will treat your infusion reactions based on whether you have a mild, moderate, severe, or life threatening reaction.

If you have a mild or moderate reaction, your doctor may pause your infusion or slow the speed of the infusion. Depending on how severe your reaction is, your doctor may decide to permanently stop your treatment.

Infusion reactions can occur during or after you receive the infusion of Keytruda. If you experience any of these side effects, let your doctor know right away.

Skin rash

Skin rash is a common side effect of Keytruda. With skin rashes, you may have blistering on your skin and itchiness. A skin rash can also occur if you have an allergy to Keytruda.

However, skin rash is also a symptom of other side effects of Keytruda. These may include infusion reactions and immune-mediated adverse reactions. (These side effects occur because of an overactive immune system.)

Skin rashes can range from mild to severe. Eczema is an example of a mild skin rash. Exfoliative dermatitis is a severe reaction that causes skin cells to peel off.

What to do

Talk with your doctor if you notice changes in your skin during treatment with Keytruda. Your doctor can help determine what is causing your skin condition and what treatment may be needed.

Depending on the cause and severity of your skin rash, your doctor may treat it differently. A severe skin reaction, such as exfoliative dermatitis, may lead to permanently stopping treatment with Keytruda. For mild skin reactions, your doctor may prescribe a steroid cream or ointment, such as hydrocortisone cream.

Hair loss

Hair loss was a common side effect reported in clinical studies that looked at Keytruda in combination with chemotherapy or bevacizumab (Avastin). Chemotherapy drugs often have hair loss as a common side effect. However, hair loss was not reported when Keytruda was used alone.

With hair loss, you may lose hair anywhere on your body, including your head, face, and legs. For some people, hair loss is bothersome or impacts their quality of life.

What to do

If you experience hair loss while receiving Keytruda, talk with your doctor. They may recommend treatments to help manage hair loss, such as cold cap therapy. This treatment requires wearing a cap that cools your scalp before, during, and after treatment.

If hair loss affects your quality of life, talk with your doctor. They can recommend ways to cope with this side effect.

Hypothyroidism

Hypothyroidism (low thyroid hormone level) may occur with Keytruda. Different thyroid disorders are common with this drug. Keytruda can overstimulate the immune system, which means the body may start destroying cells, including those in the thyroid.

Symptoms of hypothyroidism may include:

  • fatigue
  • weight gain
  • dry skin
  • coarse and brittle hair
  • difficulty tolerating cold temperatures
  • slow heart rate
  • irregular periods in females* who menstruate

* Sex and gender exist on spectrums. In this article, use of the term “female” refers to sex assigned at birth.

What to do

If you are experiencing any symptoms of hypothyroidism, talk with your doctor. They may recommend a blood test to check your thyroid hormone levels. If this test shows that your levels are low, your doctor may prescribe a thyroid hormone supplement such as levothyroxine (Synthroid). Your doctor will continue to check your thyroid levels to make sure the new medication is working.

Depending on the severity of your hypothyroidism, your doctor may decide to stop your treatment with Keytruda.

Hepatitis or liver damage

Keytruda may cause hepatitis or damage to your liver. This may be because Keytruda can cause an overactive immune system, which means the body can start destroying organs, including the liver. However, these side effects were not common in the drug’s clinical studies.

Symptoms of liver damage may include:

  • jaundice
  • severe nausea
  • severe vomiting
  • bruising easily
  • bleeding

In addition to these symptoms, your liver enzymes may be elevated. To check your liver enzymes, your doctor will order a blood test.

What to do

If you notice symptoms of liver damage, talk with your doctor. They may recommend steroid treatment, such as prednisone (Rayos).

In some situations, immunosuppressant therapy may be required, such as azathioprine (Imuran).

Also, depending on the severity of your liver damage, your doctor may temporarily or permanently stop Keytruda.

Allergic reaction

As with most drugs, some people can have an allergic reaction after taking Keytruda. A more severe allergic reaction is rare but possible.

Possible symptoms of mild and serious allergic reactions are listed in the table below.

Mild allergic reaction symptoms Serious allergic reaction symptoms
• itching trouble breathing
rash • swelling in your throat or mouth
flushing • swelling under your skin, possibly in your hands, feet, lips, or eyelids

If you have an allergic reaction to Keytruda, call your doctor right away. This is important because the reaction could become severe.

However, if you’re having a medical emergency or your symptoms feel life threatening, call 911 or your local emergency number.

Keytruda: Precautions

Be sure to talk with your doctor about your health history before taking Keytruda. This drug may not be the right treatment option if you have certain medical conditions or other factors that affect your health.

The conditions and factors to consider include those described below.

History of radiation therapy. Keytruda may cause pneumonitis (inflammation in your lungs). However, it’s more common in people who have had chest radiation treatment in the past. To treat pneumonitis, you might need to take steroids. In some situations, your doctor may pause or stop your treatment with Keytruda.

History of allogeneic hematopoietic stem cell transplantation. People who receive a treatment called allogeneic hematopoietic stem cell transplantation (HSCT) before or after Keytruda can have serious side effects. Serious transplant-related complications may occur that can lead to donor cells destroying your healthy cells. If you’ve received or plan to receive allogeneic HSCT, your doctor will monitor your symptoms closely to make sure you’re not having complications. Your doctor will weigh the benefits and risks of prescribing Keytruda before or after receiving allogeneic HSCT.

Multiple myeloma. A possible treatment for multiple myeloma may be a thalidomide analogue, such as lenalidomide (Revlimid), and dexamethasone (Hemady). If you are receiving this treatment combination, Keytruda may not be right for you. This drug combination taken with Keytruda may increase your risk of death. To prevent this possibly fatal drug combination, tell your doctor if you’re receiving medication for multiple myeloma. Your doctor will likely prescribe another medication in this situation.

Allergic reaction. If you’ve had an allergic reaction to Keytruda or any of its ingredients, your doctor will likely not prescribe Keytruda. Ask your doctor what other medications may be better options for you.

Consuming alcohol during Keytruda treatment

Some medications may interact with alcohol. Keytruda isn’t one of them.

However, before starting Keytruda, if you drink alcohol, ask your doctor or pharmacist if it’s safe for you to do so.

Pregnancy and breastfeeding during Keytruda treatment

Keytruda is not safe to use in pregnancy. Animal studies suggest that Keytruda may overstimulate the animals’ immune system. With an overactive immune system, the body may start destroying the fetus’s cells. However, animal studies don’t always show what will happen in humans.

If you’re able to become pregnant, your doctor will talk with you about what contraception to use while taking Keytruda. You must continue using birth control for 4 months after your last dose of Keytruda.

Before starting Keytruda, your doctor will order a pregnancy test. Based on how Keytruda works, children exposed to the drug during pregnancy may develop immune system disorders.

It’s unclear if Keytruda is safe during breastfeeding. However, doctors suggest that Keytruda exposure from breast milk may be unsafe. Your doctor will advise you to avoid breastfeeding while receiving Keytruda and for 4 months after your last dose.

Keytruda: What to discuss with your doctor

Talk with your doctor or pharmacist for additional information about Keytruda. If you have questions about the drug’s side effects, your pharmacist or healthcare professional can help answer them.

In addition to discussing Keytruda with your doctor, you may find the following articles helpful in learning more.

  • Overview of Keytruda. To read an overview of Keytruda, see this article.
  • Drug comparison. To learn how Keytruda compares with Opdivo, read this article.
  • Dosage information. If you’d like to know about Keytruda’s dosage, view this article.
  • Details about cancer. To learn more about cancer, which Keytruda is used to treat, see this article.

Disclaimer: Healthgrades 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.

Medical Reviewer: Melissa Badowski, PharmD, MPH, FCCP
Last Review Date: 2022 Jul 29
THIS TOOL DOES NOT PROVIDE MEDICAL ADVICE. It is intended for informational purposes only. It is not a substitute for professional medical advice, diagnosis or treatment. Never ignore professional medical advice in seeking treatment because of something you have read on the site. If you think you may have a medical emergency, immediately call your doctor or dial 911.