Key Takeaways
- Keytruda may cause side effects that range from mild to serious. Common effects include fatigue, rash, diarrhea, loss of appetite, and nausea.
- Many of Keytruda’s serious side effects happen due to an overactive immune system. This can cause inflammation (damage and swelling) in various parts of the body.
- Side effects can vary depending on whether Keytruda is used by itself or with other cancer drugs.
- Some side effects may occur during Keytruda treatment, while others can happen after stopping treatment.
Keytruda is a
Keytruda’s active ingredient is pembrolizumab. The drug is given by intravenous (IV) infusion. (An IV infusion is an injection into a vein given over a period of time.)
Keep reading to learn about the common, mild, and serious side effects that Keytruda can cause. For more information on the drug, including details about all of the cancers it treats, see this Keytruda overview.
Examples of Keytruda’s commonly reported side effects include:
- diarrhea
- fatigue (low energy)
- loss of appetite
- nausea
- itchy skin or rash*
* To learn more about this side effect, see the “Side effects explained” section later in this article.
Read on to learn about other possible side effects of Keytruda.
Examples of mild side effects that have been reported with Keytruda include:
- abdominal pain
- constipation
- cough
- diarrhea
- fatigue
- 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 the “Side effects explained” section later in this article.
In most cases, these side effects should be temporary, lasting a few days or weeks. 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. Do not stop Keytruda treatment unless your doctor tells you to.
Keytruda may cause mild side effects other than the ones listed previously. See the Keytruda prescribing information for more details.
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) of body tissues. Examples include:
- adrenal insufficiency
- arthritis
- colitis, which affects the colon
- encephalitis, a brain condition
- 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 problems, including type 1 diabetes and diabetic ketoacidosis
- severe skin reactions, including Stevens-Johnson syndrome and toxic epidermal necrolysis
- hormone problems, which can include:
- 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 or bone marrow (where most blood cells are made)
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 the “Side effects explained” section later in this article.
If you develop serious side effects during Keytruda treatment, contact 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.
Note: After the Food and Drug Administration (FDA) approves a drug, it tracks and reviews side effects of the medication. Sharing your experience helps make medication safer for everyone by giving doctors and researchers more information about how the drug works in real life. If you develop a side effect during Keytruda treatment and want to tell the FDA about it, visit MedWatch or call 800-FDA-1088.
In most cases, Keytruda’s side effects should be temporary. Most should go away soon after you start or stop the drug, usually within a few days or weeks.
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:
| Side effect | Area of inflammation | Long-term problem |
|---|---|---|
| encephalitis | brain | loss of muscle function and memory or speech problems |
| hepatitis | liver | liver damage |
| pneumonitis | lungs | pulmonary fibrosis (scar tissue on your lungs) |
| uveitis | eyes | vision loss, cataracts, or glaucoma |
These are not all the long-term side effects that Keytruda may cause. If you have questions about what to expect long term while receiving Keytruda, talk with your doctor or pharmacist. Do not stop your Keytruda treatment unless your doctor recommends it.
Get answers to some frequently asked questions about Keytruda’s side effects.
When do Keytruda side effects usually start?
It’s hard to say. Keytruda side effects can happen any time after you start receiving this drug. Some may even occur after you stop Keytruda treatment.
Keytruda is given by intravenous (IV) infusion, which is an injection into a vein that’s given over time. You may have side effects called infusion reactions from this procedure. Examples of infusion reactions include fever, chills, low blood pressure, and a low level of oxygen in the blood. Sometimes, infusion reactions can be severe.
A healthcare professional will monitor you for infusion reactions while you’re receiving doses of the drug.
When you might develop side effects may also depend on whether you receive Keytruda alone or in combination with other drugs. Having certain risk factors might also affect the timing of side effects occurring. (For more information, see the “Warnings for Keytruda” section later in this article.)
Your doctor can tell you more about when certain side effects might happen.
Could I experience any eye problems while receiving 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 receiving 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:
Tell your doctor right away if you have any symptoms of eye problems while receiving 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. 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 occurred when Keytruda was given with chemotherapy in studies:
- headache
- peripheral neuropathy (numbness or tingling in your hands or feet)
- mouth sores
- insomnia
- joint pain
If you have questions about what to expect when receiving 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 atypical 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 receiving 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 area where there’s pain
- resting the area where there’s pain
- stretching the affected muscle
- taking over-the-counter (OTC) pain relievers, such as acetaminophen (Tylenol) or ibuprofen (Advil, Motrin)
Before taking OTC drugs with Keytruda, talk with your doctor or pharmacist. Also, 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 receiving 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 receiving 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 reduce 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, try to avoid hair styling tools that are harsh on hair. These include blow dryers and hair straighteners. You may also want to avoid bleaching or coloring your hair so it stays healthy enough to grow.
If you experience bothersome hair loss during Keytruda treatment, talk with your doctor about ways to help with this side effect.
Itchy skin or rash
You may have itchy skin or rash from receiving 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 receiving 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 of a severe skin reaction from Keytruda, talk with your doctor.
Allergic reactionFor some people, Keytruda can cause an allergic reaction. In general, symptoms of an allergic reaction can be mild or serious.
What might helpIf 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 and can determine whether you should continue Keytruda 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.
If your doctor confirms you’ve had a serious allergic reaction to Keytruda, they may have you switch to a different treatment.
Keytruda is used to treat certain types of cancer in some children. (For information about the cancers Keytruda can treat in children, see this Keytruda overview.)
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
- vomiting
Talk with your child’s doctor about their risk of 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 start Keytruda. Factors to consider include:
Allergic reaction: If you’ve had an allergic reaction to Keytruda or any of its ingredients, you should not receive Keytruda. Ask your doctor what other medications are better options for you.
Receiving certain other treatments for multiple myeloma: Receiving 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 starting Keytruda, tell your doctor if you’re having any treatments for multiple myeloma.
Received an organ transplant: Before starting Keytruda, tell your doctor if you’ve had an organ transplant. Keytruda can raise the risk of 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 receiving Keytruda.
Received or plan to receive a stem cell transplant: Before starting 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 of 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 receive.
Alcohol and Keytruda
It should be safe to drink alcohol while receiving Keytruda.
But be aware that alcohol can cause side effects that are similar to some of Keytruda’s. These include diarrhea, fatigue, 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 receiving Keytruda.
Pregnancy and breastfeeding while receiving Keytruda
You should not receive Keytruda while pregnant or breastfeeding.
Keytruda hasn’t been studied during pregnancy. But based on how the drug works, Keytruda may cause harm to children born to females who received the drug during pregnancy.
For this reason, you should use birth control during Keytruda treatment 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 whether Keytruda can pass into breast milk. To be safe, you should not breastfeed while receiving 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.
Note: In this article, we use the term “female” to refer to someone’s sex assigned at birth. To learn more, see this article on the difference between sex and gender.
Q:
Will I need to have any lab tests to monitor for side effects from Keytruda?
AnonymousA:
Yes, your doctor will need to monitor various lab results to reduce your risk of side effects while receiving Keytruda.
The tests they order may depend on the type of cancer you have or other drugs that you’re using with Keytruda. For instance, your doctor will monitor your liver function for the development of liver injury. They may also monitor the amount of creatinine in your blood to check whether you have kidney problems.
Talk with your doctor about what lab tests they recommend for you during Keytruda treatment and how frequently you should have them.
The Healthline Pharmacist TeamAnswers represent the opinions of our medical experts. All content is strictly informational and should not be aconsidered medical advice.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.