Keytruda (pembrolizumab) is a prescription brand-name medication. It’s approved by the Food and Drug Administration (FDA) to treat many types of cancer in adults and certain children. It may be used to treat lung cancer, melanoma, and bladder cancer, as well as other types of cancer.

Here are some fast facts on Keytruda treatment:

  • Active ingredient: pembrolizumab, which is a biologic
  • Drug class: programmed cell death protein 1 (PD-1) inhibitor
  • Drug form: intravenous (IV) infusion

Like other drugs, Keytruda can cause side effects. Read on to learn about potential common, mild, and serious side effects. For a general overview of Keytruda, including a full list of conditions it’s used to treat, see this article.

Keytruda can cause certain side effects, some of which are more common than others. These side effects may be temporary, lasting a few days or weeks. But if the side effects last longer than that, bother you, or become severe, be sure to talk with your doctor or pharmacist.

These are just a few of the more common side effects reported by people who took Keytruda in clinical trials:

It’s important to note that these side effects can vary depending on whether you are using Keytruda in combination with other drugs to treat your condition. It’s also important to note that side effects of Keytruda aren’t known to vary depending on the type of cancer it’s treating, such as lung cancer.

Mild side effects can occur with Keytruda use. This list doesn’t include all possible mild side effects of the drug. For more information, you can refer to Keytruda’s medication guide.

Mild side effects that have been reported with Keytruda include:

These side effects may be temporary, lasting a few days or weeks. But if the side effects last longer than that, bother you, or become severe, be sure to talk with your doctor or pharmacist.

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 on this side effect, see “Side effect specifics” below.

Keytruda may cause serious side effects. The list below may not include all possible serious side effects of the drug. For more information, you can refer to Keytruda’s medication guide.

If you develop serious side effects while taking Keytruda, 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.

Serious side effects that have been reported and their symptoms include:

  • Severe infusion reactions (side effects that occur during or shortly after receiving a Keytruda infusion). Symptoms can include:
    • chills
    • skin itching or a rash
    • trouble breathing
  • Severe immune system reactions that involve inflammation (damage and swelling). Symptoms can vary widely depending on which area of the body is affected, and can include:
    • fever, headache, chest tightness, or dry cough due to pneumonitis (inflammation in your lungs)
  • Eye-related side effects.*
  • Severe skin reactions.*
  • Confusion.*
  • Allergic reaction.*

* For more information on this side effect, see “Side effect specifics” below.

Long-term side effects

When you’re considering Keytruda treatment, you may want to know how long Keytruda side effects last.

The more common and mild side effects of Keytruda are usually temporary. Some may go away once your body gets used to the drug, within a few days or weeks. Others may continue for as long as you’re receiving Keytruda treatment.

However, some serious side effects of Keytruda could cause long-term effects. Although less common, severe immune system reactions can happen with Keytruda. These can occur because Keytruda may trigger your immune system to attack your body and cause inflammation. Depending on which area of your body is affected, the inflammation could cause long-term damage.

If you have questions about long-term side effects of Keytruda, talk with your doctor.

Keytruda can be used to treat skin cancer, lymphoma, and other solid cancer tumors in certain children. Some side effects of Keytruda are more common in children than in adults. These may include:

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

Eye-related side effects

Ocular (eye-related) side effects have been reported in people taking Keytruda. Some examples of these eye problems include:

  • Uveitis (inflammation* of the uvea, which is the middle layer of your eye). This can cause eye pain, watering, and itchiness.
  • Inflammation* of the white part of your eye. This can cause eye redness and itching.
  • Retinal detachment (a condition in which the back inner lining of your eye starts to separate from the rest of your eye). This can cause sudden vision loss.

However, eye-related side effects were rare during clinical studies of Keytruda.

* Inflammation refers to damage and swelling.

What you can do

If you notice any eye or vision problems after starting Keytruda, do not wait to see if your symptoms get better. It’s important to call your doctor right away or get emergency medical care. You may be referred to an ophthalmologist (eye doctor) immediately.

If you get immediate treatment for possible eye problems (which may include surgery in severe cases), your eyes will have a better chance of recovering. Your doctor may have you stop taking Keytruda if you have eye-related side effects.

Even if you’re not having vision problems, it’s important to visit your eye doctor regularly while you’re receiving Keytruda. They can monitor you for any vision changes.

Skin reactions

Serious skin reactions, such as certain types of severe rashes, have occurred in clinical studies of Keytruda. These reactions included Stevens-Johnson syndrome (SJS) and toxic epidermal necrolysis (TEN). Both of these conditions cause symptoms such as:

  • severe, painful blisters on your body
  • your skin peeling off in layers
  • flu-like symptoms, such as fever, chills, and body aches

SJS and TEN can be life threatening.

Note: A mild, itchy skin rash is a common side effect of Keytruda. But the serious skin reactions described above are different from this mild side effect and require immediate medical care.

What you can do

If you develop a skin reaction that involves blisters, or any symptoms that seem severe, talk with your doctor right away. They may recommend that you call 911 or seek emergency medical care.

If you have a severe skin reaction, your doctor will likely have you permanently stop Keytruda treatment.

Pain in muscles or bones

Bone pain and muscle pain are common side effects of Keytruda.

Bone pain is often described as a deep, dull ache in one or more bones. The pain is usually there regardless of whether you’re moving or at rest. You may also notice pain, stiffness, or swelling in your joints.

With muscle pain, your muscles may feel very sore, especially with movement.

The severity of muscle or bone pain from Keytruda can vary. If you already have conditions that affect your muscles or bones, such as arthritis, these side effects can be more severe.

What you can do

Muscle or bone pain from Keytruda tends to be mild and easily managed, in most cases. The following home remedies may be helpful:

  • taking an over-the-counter pain reliever, such as Tylenol (acetaminophen), as long as your doctor approves
  • heat therapy and cold therapy
  • “listening” to your body and resting when you need to

If these remedies aren’t helpful, or if you have pain that becomes severe, talk with your doctor. They may recommend a prescription pain medication. They may also suggest seeing an orthopedic (bone) specialist.

Confusion

Confusion can occur when receiving Keytruda treatment. Confusion may seem like a mild side effect, but it could be a sign of something more serious.

Keytruda can cause severe immune system reactions in which your immune system attacks your body. This can cause inflammation (swelling and damage), which can lead to varied symptoms depending on the area of the body that’s affected. It’s possible that confusion could be a sign you’re developing an immune system reaction from Keytruda.

Confusion could occur if inflammation is building up in certain areas of your body, such as:

  • your nervous system (brain and spinal cord)
  • your adrenal glands (glands located on top of your kidneys that make a hormone called adrenaline)

What you can do

If you or those around you notice any new or unusual confusion after you start Keytruda treatment, do not wait to see if this gets better on its own. It’s important to talk with your doctor about this right away.

Your doctor may recommend that you be evaluated for an immune system reaction. Depending on this evaluation, you may need treatment in a hospital. Your doctor will likely have you stop taking Keytruda if you have an immune system reaction.

Hair loss

In clinical studies that looked at Keytruda in combination with chemotherapy, hair loss was one of the most common side effects. Hair loss is a common side effect of many chemotherapy drugs. Hair loss was not seen when Keytruda was used on its own.

Keytruda can cause severe immune system reactions in which your immune system attacks your body. This can cause inflammation (damage and swelling), which can lead to varied symptoms depending on the area of the body that’s affected. Hair loss could be a sign that Keytruda is causing inflammation of your thyroid gland. Your thyroid is a gland in your neck that produces certain hormones.

Other symptoms of thyroid gland inflammation can include weight loss or gain, increased sweating or feeling cold, mood changes, and heart rate changes. Diarrhea or constipation are also possible symptoms.

What you can do

Hair loss is a very common side effect of many cancer treatments. But this side effect usually goes away when your treatment ends. And after you’ve completed treatment, your hair will start to grow back.

However, you should always tell your doctor if you’re losing hair. This is especially important if you’re taking Keytruda on its own (without chemotherapy) or if you’re having other symptoms of thyroid inflammation, as described above.

Your doctor may suggest a blood test to check your thyroid hormone levels. They’ll also check for other signs of an immune system reaction that could be affecting your thyroid. Depending on what your doctor determines to be the cause of your hair loss, they may have you stop Keytruda treatment.

Allergic reaction

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

Symptoms can be mild or serious and can include:

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

What you can do

For mild symptoms of an allergic reaction, call your doctor right away. They may recommend ways to ease your symptoms and determine whether you should keep taking Keytruda. But if your symptoms are serious and you think you’re having a medical emergency, immediately call 911 or your local emergency number.

Be sure to talk with your doctor about your health history before you take Keytruda. This drug may not be the right treatment for you if you have certain medical conditions or other factors that affect your health. The conditions and factors to consider include:

Autoimmune disease. If you have an autoimmune condition, Keytruda treatment could possibly worsen your condition. This is because of the possible risk of severe immune system reactions that can occur with Keytruda. (See the “Side effects specific” section above for details.) Make sure to talk with your doctor about this risk if you have an autoimmune disease.

Prior stem cell transplant. If you’ve received an allogenic stem cell transplant (stem cells from a donor), Keytruda may increase your risk of graft-versus-host-disease (GVHD). With GVHD, your immune system attacks the transplanted stem cells. If you’ve had a stem cell transplant in the past, talk with your doctor about this risk before starting Keytruda.

Lung or breathing problems. If you have lung or breathing problems such as chronic obstructive pulmonary disease (COPD) or asthma, it’s possible that taking Keytruda could worsen your symptoms. Talk with your doctor about whether Keytruda’s potential benefits outweigh the risks for you.

Liver disease. If you have liver problems or have had liver problems in the past, Keytruda may not be safe for you. Be sure to let your doctor know about your liver problems when Keytruda treatment is being considered. Depending on your condition, they may suggest other cancer treatment options.

Use of certain drugs for multiple myeloma. Taking Keytruda along with certain drugs that treat multiple myeloma may be harmful. These include thalidomide-like drugs taken with dexamethasone. The combination of these drugs with Keytruda has been linked to an increased risk of death. If you’re receiving these treatments for multiple myeloma, your doctor will talk with you about other cancer treatments that would be safer for you.

Nervous system problems, such as myasthenia gravis. Keytruda treatment may cause myasthenia gravis to get worse. If you have myasthenia gravis or another nervous system condition, be sure to talk with your doctor. They’ll discuss the potential benefits and risks of Keytruda with you.

Allergic reaction. You should not take Keytruda if you’ve ever had an allergic reaction to the drug or any of its ingredients. Talk with your doctor about which other treatments are better choices for you.

Pregnancy. Keytruda can cause harmful effects in a developing fetus. It’s recommended to use an effective form of birth control during Keytruda treatment and for 4 months after your Keytruda treatment ends. For more details, see the “Pregnancy and breastfeeding while taking Keytruda” section just below.

Breastfeeding. Keytruda should not be used while breastfeeding. For details, see the “Pregnancy and breastfeeding while taking Keytruda” section below.

Alcohol use with Keytruda

Alcohol isn’t known to cause any interactions with Keytruda.

But drinking alcohol, especially in large amounts, could cause some of the same possible side effects of Keytruda. These may include:

If you drink alcohol, talk with your doctor about whether any amount of alcohol is safe for you during Keytruda treatment.

Pregnancy and breastfeeding while taking Keytruda

It’s not safe to receive Keytruda during pregnancy. The drug could cause harmful effects in a developing fetus. For this reason, it’s recommended to use an effective form of birth control during Keytruda treatment. Birth control should be continued until at least 4 months after your last dose. This is because Keytruda stays in your system for a few months after you stop treatment.

If you’re sexually active and you or your partner can become pregnant, talk with your doctor about your birth control needs while you’re using Keytruda.

Keytruda should not be used while breastfeeding. The drug could cause harm in a child who’s breastfed by a person who’s taking Keytruda. And it’s recommended to wait at least 4 months after your last dose of Keytruda before breastfeeding.

Before starting Keytruda, talk with your doctor about any concerns you may have about pregnancy or breastfeeding.

Like other drugs that treat cancer, Keytruda comes with the potential for mild and serious side effects. If you’d like to learn more about Keytruda, talk with your doctor or pharmacist. They can help answer any questions you have about side effects from taking the drug.

Besides talking with your doctor, you can do some research on your own. These articles might help:

  • More information on Keytruda. For details on other aspects of Keytruda, refer to this article.
  • Drug comparison. To learn how Keytruda compares with other drugs, read the comparison articles on Opdivo and Imfinzi.
  • A look at cancer. For details on cancer, see our cancer hub. You can also refer to our list of related articles.

Disclaimer: Medical News Today 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.