Zydelig (idelalisib) is a brand-name prescription medication. It’s approved by the Food and Drug Administration (FDA) to treat the following types of cancer in adults in certain situations:

Zydelig is used to treat cancers that have relapsed. The term “relapsed” means the cancer improved with treatment, but then it returned or worsened. Zydelig is typically prescribed as a long-term treatment.

Here are some other fast facts about Zydelig:

  • Active ingredient: idelalisib
  • Drug class: kinase inhibitor
  • Drug form: oral tablet

Like other drugs, Zydelig can cause side effects. Read on to learn about potential common, mild, and serious side effects. For a general overview of Zydelig, including details about its uses, see this article.

* The FDA granted Zydelig accelerated approval for SLL and FL. This type of approval is based on outcomes from early clinical trials. Full FDA approval depends on the results from further clinical trials.

Zydelig can cause certain side effects. Some of them are more common than others. Also, some side effects vary by the condition Zydelig is treating. If you have questions about common side effects of Zydelig for your condition, talk with your doctor or pharmacist.

In clinical trials, some side effects reported most often by people who took Zydelig alone or in combination with other cancer medication included:

* To learn more about this side effect, see the “Side effect specifics” section below.
† For more information about this side effect, see the “FAQs about the side effects of Zydelig” section below.

You may have mild side effects while taking Zydelig. We’ve listed some known mild side effects of Zydelig below. Keep in mind this list doesn’t include all possible mild side effects of the drug. And some may vary by the condition Zydelig is treating. To learn more, refer to Zydelig’s prescribing information.

When taken alone or in combination with other cancer medication, mild side effects of Zydelig can include:

* To learn more about this side effect, see the “Side effect specifics” section below.
† For more information about this side effect, see the “FAQs about the side effects of Zydelig” section below.

In general, mild side effects of Zydelig should be manageable. Or they may ease with continued use of the drug. However, if any side effects persist, bother you, or become severe, talk with your doctor or pharmacist right away.

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 Zydelig and want to tell the FDA about it, visit MedWatch.

Zydelig may cause serious side effects. Some were commonly reported in clinical trials of Zydelig when taken alone or in combination with other cancer medication. Also, the list below may not include all possible serious side effects of the drug.

Ask your doctor or pharmacist about your risk of serious side effects with Zydelig for your condition. And for more information, refer to Zydelig’s prescribing information.

If you develop serious side effects while taking Zydelig, call your doctor right away. If your symptoms 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:

* Zydelig has a boxed warning for this side effect. This is a serious warning from the Food and Drug Administration (FDA). For details, see “Boxed warnings” in the “Side effect specifics” section below.
† For more information about this side effect, see the “Side effect specifics” section below.

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

Fever

Fever can occur with Zydelig. This was a commonly reported side effect in clinical trials when Zydelig was taken alone or in combination with other cancer medication.

Also, fever can be a symptom of certain serious side effects from Zydelig, including:

* Zydelig has a boxed warning for this side effect. This is a serious warning from the Food and Drug Administration (FDA). See “Boxed warnings” below for details.

What you can do

If you have a fever when taking Zydelig, talk with your doctor right away. They’ll order tests to check your blood cell counts. If you have other symptoms, they may recommend other tests to see if you have developed serious side effects.

To manage your fever, your doctor will treat the cause. For example, they may prescribe an antibiotic to clear up an infection. In some cases, they may pause or end your Zydelig treatment. Keep in mind that you should not stop taking your medication without your doctor’s approval.

If you have a low fever without a serious cause, your doctor may recommend taking ibuprofen (Advil) or naproxen (Aleve). Typically, it’s best to avoid acetaminophen (Tylenol) with Zydelig. This is because acetaminophen can harm your liver.

You can also try nondrug fever relievers, such as:

  • taking cool baths
  • applying cool compresses
  • drinking cold water
  • cutting out spicy foods
  • avoiding hot places

Fatigue

Zydelig treatment may cause fatigue, which refers to low energy.

Fatigue was a commonly reported side effect in clinical trials of Zydelig when the drug was taken alone or in combination with other cancer medication. It may also be a symptom of serious side effects of the drug, such as neutropenia or severe liver problems.*

* Zydelig has a boxed warning for this side effect. This is a serious warning from the Food and Drug Administration (FDA). See “Boxed warnings” below for details.

What you can do

If you experience fatigue with Zydelig, talk with your doctor. They’ll likely order lab tests to check your blood cell counts and liver health. Depending on other symptoms you may have, they can suggest additional tests. Once your doctor has discovered the cause, they can treat it.

These tips may also help if you feel fatigued:

  • Take short naps throughout the day.
  • Ask family or friends to help out with errands or household chores.
  • Drink plenty of water and eat nutritious foods.

Feeling less hungry than usual

Zydelig treatment can cause reduced appetite. This side effect was reported in certain clinical trials of Zydelig when it was taken alone or in combination with other cancer medication.

When you feel less hungry than usual, you may not get enough energy or nutrients from your diet. This can lead to weight loss, weakness, or fatigue.*

* To learn more, see “Fatigue” above.

What you can do

If you feel less hungry than usual, it may help to work with your doctor to manage other side effects that curb your appetite. These can include nausea, vomiting, and mouth sores. You can also try eating high-calorie snacks or small meals throughout the day instead of larger meals. In addition, a dietitian may be able to help create an eating plan that works for you.

If you lose weight because you’re not hungry, your doctor may recommend calorie-rich shakes or prescribe medication to increase your appetite.

Boxed warnings

Zydelig has boxed warnings. Boxed warnings are the most serious warnings from the FDA. The boxed warnings for Zydelig include:

Serious diarrhea or colitis. Zydelig can cause diarrhea that may be serious or, in rare cases, lead to death. While taking the medication, you may also develop colitis, which is inflammation in your colon. Diarrhea can occur anytime during Zydelig treatment. Other drugs, such as rituximab (Rituxan), can also cause diarrhea. So if you take Zydelig with them, your risk of the condition may increase.

Pneumonitis. In rare cases, Zydelig can cause pneumonitis (inflamed lung tissue) that may be severe and, in certain instances, lead to death. This side effect was reported in clinical trials of Zydelig when the drug was taken in combination with other cancer medication.

Serious infection. While taking Zydelig, you may develop a serious infection that can, in some cases, lead to death. Serious infections were commonly reported in clinical trials of Zydelig when it was taken alone or in combination with other cancer medication.

The most commonly reported serious infections included pneumonia and febrile neutropenia (fever from low levels of a certain white blood cell). Sepsis, a dangerous reaction to an infection, was also common. Other serious infections are rare but possible. These include a fungal lung infection called Pneumocystis jirovecii pneumonia and cytomegalovirus infection, which is caused by a herpes virus.

Tear in the wall of the intestines. Zydelig can cause intestinal perforation, which is a tear in the wall of the intestines. This may be serious, and in rare cases, lead to death.

Severe liver problems. Zydelig may cause severe liver problems that may, in rare cases, lead to death. Your doctor will order blood tests to check your liver health before and during treatment with the drug. Your risk may be higher than usual for this side effect if you take other drugs that cause liver damage. Liver problems typically occur within the first 3 months of starting Zydelig treatment.

What you can do

While taking Zydelig, talk with your doctor right away if you have any new or worsening symptoms. If they seem life threatening or like a medical emergency, immediately call 911 or your local emergency number, or get medical care. Here’s some additional information about Zydelig’s boxed warnings and what you can do about them:

How to manage serious diarrhea or colitis. Talk with your doctor right away if your daily bowel movements increase by six or more during Zydelig treatment. If you have serious diarrhea or colitis with Zydelig, they may suggest certain treatments. Or your doctor may suggest lowering your dosage or having you stop taking the drug.

Talk with your doctor about ways to manage mild or bothersome diarrhea while taking Zydelig. They can advise you on staying hydrated and may recommend electrolyte solutions, a special diet, or medication.

How to manage serious infection. Doctors typically will not prescribe Zydelig treatment if you have an infection. While taking the medication, talk with your doctor right away if you have a fever, cough, chills, body aches, or other infection symptoms. If you have an infection, you may need to pause Zydelig treatment until the infection clears up.

Your doctor will monitor you for serious infections, such as pneumonia. If you develop one, your doctor may have you stop taking Zydelig.

Also, you may need to take medication to help prevent certain infections during treatment. Be sure to take steps to avoid infection-causing germs, too. See the “FAQs about the side effects of Zydelig” section below for tips on how to help prevent infections.

How to manage a tear in the wall of the intestines. Talk with your doctor right away if you have symptoms of this condition, such as new or worsening diarrhea, abdominal pain, chills, fever, nausea, or vomiting. If you have a tear in your intestinal wall with Zydelig, your doctor will likely have you stop treatment.

How to manage pneumonitis. Talk with your doctor right away if you have new or worsening shortness of breath, cough, wheezing, or difficulty breathing with Zydelig. If you have such lung symptoms, your doctor may check your lung health with certain tests. This can include looking at your blood oxygen level.

If you develop pneumonitis with Zydelig, your doctor may treat the condition with corticosteroids, such as prednisone (Rayos). And they’ll most likely stop your Zydelig treatment.

How to manage severe liver problems. While taking Zydelig, talk with your doctor right away if you notice symptoms of liver damage. These can include pain in the upper side of your abdomen, unexplained weight loss, and fatigue. Other symptoms may include jaundice and unusual bleeding or bruising.

During Zydelig treatment, it’s important not to take other medications that may harm your liver, such as acetaminophen (Tylenol). It’s recommended that you avoid alcohol, too*.

Your doctor will order blood tests to check your liver health. So be sure to keep all of your lab appointments. If you have liver problems from Zydelig, your doctor may change your dosage or stop your treatment.

* To learn more, see “Alcohol and Zydelig” in the “Precautions for Zydelig” section below.

Allergic reaction

As with most drugs, Zydelig can cause an allergic reaction in some people, such as skin rash. Various types of rashes were commonly reported in clinical trials of Zydelig when the drug was taken alone and in combination with other cancer medication.

A severe, life threatening allergic reaction called anaphylaxis is also possible after taking Zydelig. However, it’s not clear whether anaphylaxis occurred in clinical trials.

Symptoms of an allergic reaction may be mild or serious and can include:

  • skin rash
  • itching
  • flushing
  • 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 you can do

For mild symptoms of an allergic reaction, talk with your doctor right away. They’ll recommend ways to ease your symptoms and determine whether you should keep taking Zydelig. If you have serious symptoms or think you’re having a medical emergency, immediately call 911 or your local emergency number.

Zydelig may cause several side effects. Below are answers to some frequently asked questions about the drug’s side effects.

What can I do to help prevent infection while taking Zydelig?

During Zydelig treatment, you can take several steps to help prevent infection,* such as:

  • washing your hands often with soap and water
  • using hand sanitizer if you can’t wash your hands
  • avoiding crowds, as well as friends and family who are sick
  • disinfecting your phone, devices, and surfaces you touch often
  • staying current with your vaccines, such as a yearly flu shot
  • taking care of your overall wellness by practicing good sleeping habits, drinking plenty of water, and eating nutritious foods

Keep in mind that getting treatment for an infection early on may help prevent it from becoming severe. So while taking Zydelig, talk with your doctor right away if you have symptoms of an infection. These can include fever, chills, cough, or body aches.

In some cases, your doctor may prescribe medication to help prevent a rare but serious infection called Pneumocystis jirovecii pneumonia.*

If you have additional questions about how to help prevent infections during Zydelig treatment, talk with your doctor.

* Zydelig has a boxed warning for serious infection. This is a serious warning from the Food and Drug Administration (FDA). See “Boxed warnings” in the “Side effect specifics” section above for details.

Can I take Zydelig if I had a severe skin reaction with the cancer drug duvelisib?

Probably not. It’s usually unsafe to take Zydelig if you have had a severe skin reaction with duvelisib (Copiktra). If the skin reaction was toxic epidermal necrolysis, it’s unlikely that your doctor will prescribe Zydelig.

Zydelig can cause serious skin reactions. So if you’ve had them in the past, you have an increased risk of developing them during Zydelig treatment. (See the “Precautions for Zydelig” section below to learn more.)

If you have additional questions about whether Zydelig is right for you, talk with your doctor. Together, you can plan the safest and most effective treatment for your condition.

What’s the best way to manage nausea while taking Zydelig?

Your doctor may prescribe medication to ease nausea, such as ondansetron (Zofran) or promethazine (Phenergan). You can also try nondrug treatments. Consider these tips:

Keep in mind that nausea can also be a symptom of serious side effects, such as severe liver problems,* serious infection,* or a tear in the wall of the intestines.*

While taking Zydelig, talk with your doctor if you have nausea that lasts, bothers you, or becomes severe.

* Zydelig has a boxed warning for this side effect. This is a serious warning from the FDA. See “Boxed warnings” in the “Side effect specifics” section above for details.

Talk with your doctor about your health history before you take Zydelig. This drug may not be right for you if you have certain medical conditions or factors that affect your health, including the boxed warnings listed below.

Boxed warnings

Zydelig has boxed warnings about:

These are serious warnings from the Food and Drug Administration (FDA). For details, see the “Side effect specifics” section above.

Other precautions

Be sure to talk with your doctor about your health history before you take Zydelig. This drug may not be the right cancer treatment for you if you have certain medical conditions or factors that affect your health. In addition to the boxed warnings listed above, precautions to consider include:

History of serious skin reactions. If you have had a serious skin reaction with any drug, doctors typically will not prescribe Zydelig. Examples of serious skin reactions include:

Zydelig can cause serious skin reactions. So if you’ve had them in the past, you may have an increased risk of developing them during Zydelig treatment.

Before taking Zydelig, tell your doctor about any past skin reactions. You can also ask them which treatments are safe and effective for your condition. See the “FAQs about the side effects of Zydelig” section above to learn more.

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

Alcohol and Zydelig

It’s best to avoid alcohol during Zydelig treatment.

Consuming alcohol doesn’t affect how Zydelig works to treat your condition. However, the drug may cause serious liver problems.* Drinking too much alcohol can also harm your liver. So consuming alcohol while taking Zydelig may increase your risk of liver damage.

Drinking alcohol during treatment may also worsen some of Zydelig’s side effects, such as extreme tiredness, diarrhea,* or nausea.

You can talk with your doctor to learn more.

* Zydelig has a boxed warning for this side effect. This is a serious warning from the FDA. For details, see “Boxed warnings” in the “Side effect specifics” section above.

Pregnancy and breastfeeding while taking Zydelig

Zydelig is not safe to take during pregnancy or while breastfeeding. You should also not breastfeed for 1 month after your last dose of the drug.

Zydelig hasn’t been studied in people who were pregnant or breastfeeding. The warnings are based on negative effects on fetuses during animal trials and how the drug works.

If you or your sexual partner can become pregnant, it’s recommended that you both use effective birth control during Zydelig treatment. Females* should continue to use birth control for 1 month after their last dose. Males* are advised to use birth control for 3 months after their last dose.

If you think or know you’re pregnant while taking Zydelig, talk with your doctor right away.

* Sex and gender exist on spectrums. Use of the terms “male” and “female” in this article refers to sex assigned at birth.

While taking Zydelig, it’s likely you’ll have side effects. Many of the drug’s possible side effects are mild and manageable. However, some side effects are serious and may require medical care. So your doctor may need to adjust your dosage, or pause or stop your treatment.

Because of the risk of serious side effects with Zydelig, you should keep all your doctor and lab appointments. Be sure to talk with your doctor right away if you develop new or worsening symptoms. You should also see your doctor immediately if you have a fever or other signs of infection.*

If you’d like to learn more about Zydelig, talk with your doctor or pharmacist. They can help answer any questions you have about side effects of taking the drug.

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

  • More information about Zydelig. For details about other aspects of Zydelig, refer to this article.
  • A look at your condition. To learn more about cancer, see our cancer hub or lists of articles about leukemia and lymphoma.

* Zydelig has a boxed warning for serious infection. This is a serious warning from the Food and Drug Administration (FDA). See “Boxed warnings” in the “Side effect specifics” section above for details.

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.