Many medications can cause side effects. A side effect is an unwanted response to a medication when it is taken in normal doses. Side effects can be mild or severe, temporary or permanent.

The side effects listed below are not experienced by everyone who takes Zydelig (Idelalisib). If you are concerned about side effects, discuss the risks and benefits of Zydelig (Idelalisib) with your doctor.

The following side effects have been reported by at least 1% of people taking Zydelig (Idelalisib). Many of these side effects can be managed, and some may go away on their own over time.

Contact your doctor if you experience these side effects and they are severe or bothersome. Your pharmacist may be able to advise you on managing side effects.

• cold symptoms (e.g., stuffy nose, cough)
• decreased appetite
• Diarrhea (mild)
• fatigue
• headache
• heartburn
• joint or muscle pain
• mouth sores
• nausea
• night sweats
• stomach pain
• sun sensitivity
• trouble sleeping
• vomiting

Although most of the side effects listed below don't happen very often, they could lead to serious problems if you do not seek medical attention.

Check with your doctor as soon as possible if any of the following side effects occur:

• Fever or chills
• fluid retention (e.g., swelling of the feet, ankles, or lower leg)
• rash
• severe diarrhea
• signs of breathing problems (e.g., shortness of breath, troubled breathing, wheezing, or tightness in chest, fast or irregular breathing)
• signs of dehydration (e.g., decreased urine, dry skin, dry and sticky mouth, sleepiness, dizziness, headache, thirst, confusion)
• signs of infection (symptoms may include fever or chills, severe diarrhea, shortness of breath, prolonged dizziness, headache, stiff neck, weight loss, or listlessness)
• signs of liver problems (e.g., nausea, vomiting, diarrhea, loss of appetite, weight loss, yellowing of the skin or whites of the eyes, dark urine, pale stools)
• symptoms of a urinary tract infection (e.g., pain when urinating, urinating more often than usual, low back or flank pain)

Stop taking the medication and seek immediate medical attention if any of the following occur:

• signs of a serious allergic reaction (e.g., abdominal cramps, difficulty breathing, nausea and vomiting, or swelling of the face and throat)
• signs of a severe skin reaction (e.g., blistering, peeling, a rash covering a large area of the body, a rash that spreads quickly, or a rash combined with fever or discomfort)
• symptoms of progressive multifocal leukoencephalopathy (e.g., difficulty walking, memory loss, trouble thinking, confusion, vision loss)

Some people may experience side effects other than those listed. Check with your doctor if you notice any symptom that worries you while you are taking Zydelig (Idelalisib).

100 mg
Each orange, oval-shaped, film-coated tablet debossed with "GSI" on one side and the number "100" on the other contains 100 mg of Zydelig (Idelalisib). Nonmedicinal ingredients: microcrystalline cellulose, hydroxypropyl cellulose, croscarmellose sodium, sodium starch glycolate, and magnesium stearate; film coating: Sunset Yellow FCF Aluminum Lake (FD&C Yellow No. 6), polyethylene glycol, talc, polyvinyl alcohol, and titanium dioxide.

150 mg
Each pink, oval-shaped, film-coated tablet debossed with "GSI" on one side and the number "150" on the other contains 150 mg of Zydelig (Idelalisib). Nonmedicinal ingredients: microcrystalline cellulose, hydroxypropyl cellulose, croscarmellose sodium, sodium starch glycolate, and magnesium stearate; film coating: red iron oxide, polyethylene glycol, talc, polyvinyl alcohol, and titanium dioxide.

Do not use Zydelig (Idelalisib) if you:

• are allergic to Zydelig (Idelalisib) or any ingredients of the medication
• have not previously received at least one other medication to treat CLL or two other medications to treat follicular lymphoma

There may be an interaction between Zydelig (Idelalisib) and any of the following:

• 5-ASA medications (e.g.,  Mesalamine, Olsalazine, Sulfasalazine)
• alpha-blockers (e.g., Alfuzosin, Doxazosin, Silodosin, Tamsulosin)
• antiarrhythmics (e.g., Amiodarone, Disopyramide, lidocaine, quinidine)
• anti-cancer medications (e.g., Cabazitaxel, Docetaxel, Doxorubicin, Etoposide, Ifosfamide, Irinotecan, Vincristine)
• antipsychotic medications (e.g., Clozapine, Haloperidol, Lurasidone, Quetiapine, Risperidone)
• Apalutamide
• Apixaban
• Aprepitant
• "azole" antifungals (e.g., itraconazole, ketoconazole, Voriconazole)
• bacillus Calmette-Guérin (BCG)
• Baricitinib
• benzodiazepines (e.g., Chlordiazepoxide, Clonazepam, Diazepam, Lorazepam)
• birth control medications
• Bosentan
• Buprenorphine
• Buspirone
• Calcitriol
• calcium channel blockers (e.g., Amlodipine, Diltiazem, Nifedipine, Verapamil)
• cannabis
• Cinacalcet
• Cobicistat
• Colchicine
• conivaptan
• corticosteroids (e.g., budesonide, Dexamethasone, Hydrocortisone, Prednisone)
• Cyclosporine
• Darifenacin
• Deferasirox
• Denosumab
• Domperidone
• drospirenone
• Dutasteride
• echinacea
• Eliglustat
• Enzalutamide
• Eplerenone
• ergot-containing medications (e.g., Dihydroergotamine, ergotamine, or methysergide)
• estrogens (e.g., conjugated estrogen, Estradiol, ethinyl estradiol)
• Fingolimod
• Flibanserin
• Galantamine
• Hepatitis C antivirals (e.g., elbasvir, grazoprevir, ledipasvir, sofosbuvir, velpatasvir)
• HIV integrase inhibitors (e.g., bictegravir, elvitegravir)
• HIV non-nucleoside reverse transcriptase inhibitors (NNRTIs; e.g., efavirenz, etravirine, nevirapine, rilpivirine)
• HIV protease inhibitors (e.g., atazanavir, indinavir, nelfinavir, ritonavir, saquinavir)
• Ivabradine
• Leflunomide
• Lomitapide
• lumacaftor and Ivacaftor
• Macitentan
• macrolide antibiotics (e.g., clarithromycin, erythromycin)
• maraviroc
• Mefloquine
• Methadone
• mifepristone
• Mirtazapine
• Modafinil
• narcotic pain relievers (e.g., Codeine, Fentanyl, Morphine, Oxycodone)
• Naloxegol
• Natalizumab
• nitrates (e.g., isosorbide dinitrate, isosorbide mononitrate)
• Ocrelizumab
• Ondansetron
• Oxybutynin
• Ozanimod
• phosphodiesterase 5 inhibitors (e.g., Sildenafil, Tadalafil, Vardenafil)
• Pimecrolimus
• praziquantel
• Primaquine
• progestins (e.g., Dienogest, Levonorgestrel, medroxyprogesterone, Norethindrone)
• protein kinase inhibitors (e.g., Bosutinib, Dabrafenib, Dasatinib, Erlotinib, imatinib, Lapatinib, Nilotinib, Pazopanib)
• quinine
• Raloxifene
• Repaglinide
• rifabutin
• rifampin
• Riociguat
• Roflumilast
• Romidepsin
• St. John's wort
• salmeterol
• seizure medications (e.g., Carbamazepine, Eslicarbazepine, Phenobarbital, Phenytoin)
• Sirolimus
• Solifenacin
• "statin" anti-cholesterol medications (e.g., Atorvastatin, Lovastatin, Simvastatin)
• Tacrolimus
• Tamoxifen
• Tetrabenazine
• Ticagrelor
• Timolol
• Tocilizumab
• Tolterodine
• Tolvaptan
• Tramadol
• Trazodone
•  "triptan" migraine medications (e.g., Almotriptan, Eletriptan)
• vaccines
• vilanterol
• Warfarin
• Zolpidem
• Zopiclone

If you are taking any of these medications, speak with your doctor or pharmacist. Depending on your specific circumstances, your doctor may want you to:

• stop taking one of the medications,
• change one of the medications to another,
• change how you are taking one or both of the medications, or
• leave everything as is.

An interaction between two medications does not always mean that you must stop taking one of them. Speak to your doctor about how any drug interactions are being managed or should be managed.

Medications other than those listed above may interact with Zydelig (Idelalisib). Tell your doctor or prescriber about all prescription, over-the-counter (non-prescription), and herbal medications you are taking. Also tell them about any supplements you take. Since caffeine, alcohol, the Nicotine from cigarettes, or street drugs can affect the action of many medications, you should let your prescriber know if you use them.

Before you begin using a medication, be sure to inform your doctor of any medical conditions or Allergies you may have, any medications you are taking, whether you are pregnant or breast-feeding, and any other significant facts about your health. These factors may affect how you should use Zydelig (Idelalisib).

Birth control: Women who may become pregnant should use effective birth control while taking Zydelig (Idelalisib) and for at least one month after stopping treatment. Because Zydelig (Idelalisib) may reduce the effectiveness of birth control pills, a barrier form of birth control should also be used.

Diarrhea: People receiving Zydelig (Idelalisib) have experienced severe diarrhea or inflammation of the bowel. If you have a history of inflammatory bowel disease, discuss with your doctor how Zydelig (Idelalisib) may affect your medical condition, how your medical condition may affect the dosing and effectiveness of Zydelig (Idelalisib), and whether any special monitoring is needed.

Gastrointestinal problems can cause diarrhea that may lead to dehydration (loss of too much water from the body). If you experience severe diarrhea for more than a day, or if you have diarrhea along with fever, decreased urination, dizziness, or a fast heartbeat, contact your doctor immediately.

Hypersensitivity syndrome: A Anaphylaxis (severe allergic reaction) called hypersensitivity syndrome has occurred for some people taking Zydelig (Idelalisib). Stop taking the medication and get immediate medical attention if you have symptoms of a severe allergic reaction, including fever, swollen glands, yellowing of the skin or eyes, or flu-like symptoms with skin rash or blistering.

Infection: As well as killing cancer cells, Zydelig (Idelalisib) can reduce the number of cells that fight infection in the body (white blood cells). If possible, avoid contact with people with contagious infections. Tell your doctor immediately if you notice signs of an infection, such as fever or chills, severe diarrhea, shortness of breath, prolonged dizziness, headache, stiff neck, weight loss, or listlessness. Your doctor will do blood tests regularly to monitor the number of specific types of blood cells in your blood.

Serious and sometimes life-threatening infections can occur when taking Zydelig (Idelalisib). Antibiotics are often taken to prevent infections by certain bacteria during treatment with Zydelig (Idelalisib) and for several months after stopping Zydelig (Idelalisib).

Liver function: Liver disease or reduced liver function may cause Zydelig (Idelalisib) to build up in the body, causing side effects. Zydelig (Idelalisib) may also reduce liver function and can cause liver failure. If you have liver problems, discuss with your doctor how Zydelig (Idelalisib) may affect your medical condition, how your medical condition may affect the dosing and effectiveness of Zydelig (Idelalisib), and whether any special monitoring is needed. Your doctor will want to test your liver function regularly with blood tests while you are taking Zydelig (Idelalisib).

Zydelig (Idelalisib) is not recommended for people with hepatitis or active liver disease.

Lung inflammation: Lung inflammation (pneumonitis) causing difficulty breathing has occurred on rare occasions for some people taking Zydelig (Idelalisib). This complication can be serious and sometimes fatal. If you experience new or worsening shortness of breath or cough (with or without fever) at any time while you are taking Zydelig (Idelalisib), contact your doctor immediately.

Progressive multifocal leukoencephalopathy (PML): There have been reports of PML after using Zydelig (Idelalisib). PML is a rare disorder that causes nerve damage in the brain. If you experience memory loss, vision loss, trouble thinking, or difficulty walking, contact your doctor immediately.

Sensitivity to sunlight: Zydelig (Idelalisib) may increase the sensitivity of the skin to sunlight, increasing the risk of Sunburn. Avoid exposure to sunlight for long periods of time, particularly between the hours of 10 am and 2 pm. Wear a broad-spectrum sunscreen and lip balm with an SPF of 30 or greater. If you notice any unusual skin rash or peeling, contact your doctor immediately.

Pregnancy: Zydelig (Idelalisib) should not be used during pregnancy unless the benefits outweigh the risks. If you become pregnant while taking Zydelig (Idelalisib), contact your doctor immediately.

Breast-feeding: It is not known if Zydelig (Idelalisib) passes into breast milk. If you are breast-feeding and are taking Zydelig (Idelalisib), it may affect your baby. Talk to your doctor about whether you should continue breast-feeding.

Children: The safety and effectiveness of using Zydelig (Idelalisib) have not been established for children.

Seniors: Seniors may be likely to experience severe side effects from Zydelig (Idelalisib).