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 Tykerb (Lapatinib). If you are concerned about side effects, discuss the risks and benefits of Tykerb (Lapatinib) with your doctor.

The following side effects have been reported by at least 1% of people taking Tykerb (Lapatinib). 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.

• back pain
• Constipation
• difficulty sleeping
• dry skin
• Fever
• hair loss or thinning
• headache
• indigestion
• joint pain
• loss of appetite
• mouth sores or sore mouth
• nail tenderness, infection, or swelling
• nausea
• nosebleeds
• pain in the arms or legs
• skin rash
• stomach pain
• sun sensitivity
• tingling, numbness, pain, swelling, or redness of the palms of the hands or soles of the feet
• tiredness
• 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:

• Diarrhea
• symptoms of heart problems (e.g., shortness of breath, swelling of the ankles or feet, chest pain, irregular heartbeat)
• symptoms of irregular heartbeat (e.g., chest pain, dizziness, rapid, pounding heartbeat, shortness of breath)
• symptoms of liver problems (e.g., nausea, vomiting, abdominal pain, yellowing of the skin and eyes, itchy skin, dark urine)
• symptoms of lung problems (e.g., shortness of breath or difficulty breathing, chest pain, cough)

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

• symptoms of a Anaphylaxis (severe allergic reaction) (e.g., Hives; difficulty breathing; swelling of the face, mouth, tongue, or throat)
• signs of a severe skin reaction such as blistering, peeling, a rash covering a large area of the body, a rash that spreads quickly, or a rash combined with fever or discomfort

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 Tykerb (Lapatinib).

Each yellow, oval, biconvex, film-coated tablet, with one side plain and the opposite side debossed with "GS XJG", contains Tykerb (Lapatinib) ditosylate 250 mg. Nonmedicinal ingredients: tablet core: magnesium stearate, microcrystalline cellulose, povidone, and sodium starch glycolate; coating: hypromellose, iron oxide red, iron oxide yellow, macrogol/PEG 400, polysorbate 80, and titanium dioxide.

Do not take Tykerb (Lapatinib) if you are allergic to Tykerb (Lapatinib) or any ingredients of the medication or the container.

There may be an interaction between Tykerb (Lapatinib) and any of the following:

• Aliskiren
• Amiodarone
• other anticancer medications (e.g., Docetaxel, Doxorubicin, Paclitaxel, Teniposide, Topotecan, Venetoclax, Vincristine)
• antipsychotics (e.g., Chlorpromazine, Clozapine, Haloperidol, Olanzapine, Quetiapine, Risperidone)
• Apixaban
• Aprepitant
• "azole" antifungals (e.g., ketoconazole, itraconazole, Voriconazole)
• bilastine
• Bosentan
• calcium channel blockers (e.g., Amlodipine, Diltiazem, Nifedipine, Verapamil)
• Carbamazepine
• Carvedilol
• cetirizine
• chloroquine
• Cobicistat
• Colchicine
• conivaptan
• corticosteroids (e.g., Hydrocortisone, Prednisone, Dexamethasone)
• Cyclosporine
• dabigatran
• Deferasirox
• Degarelix
• Digoxin
• Dipyridamole
• Disopyramide
• dofetilide
• Domperidone
• Dronedarone
• Edoxaban
• estrogens (e.g., conjugated estrogen, Estradiol, ethinyl estradiol)
• Fentanyl
• "gliptin" diabetes medications (e.g., Linagliptin, Saxagliptin, Sitagliptin)
• grapefruit juice
• Hepatitis C antivirals (e.g., daclatasvir, ledipasvir, sofosbuvir, velpatasvir)
• HIV non-nucleoside reverse transcriptase inhibitors (NNRTIs; e.g., delavirdine, efavirenz, etravirine, nevirapine)
• HIV protease inhibitors (e.g., atazanavir, indinavir, ritonavir, saquinavir)
• Lomitapide
• Loperamide
• macrolide antibiotics (e.g., clarithromycin, erythromycin)
• Methadone
• Methotrexate
• mifepristone
• Modafinil
• Nadolol
• Phenobarbital
• Phenytoin
• primidone
• procainamide
• other protein kinase inhibitors (e.g., Pazopanib, Sunitinib)
• Prucalopride
• quinidine
• quinine
• quinolone antibiotics (e.g., ciprofloxacin, Norfloxacin, Ofloxacin)
• Ranitidine
• rifabutin
• rifampin
• Riociguat
• Romidepsin
• St. John's wort
• selective serotonin reuptake inhibitors (SSRIs; e.g., Citalopram, Fluoxetine, Paroxetine, Sertraline)
• serotonin antagonists (anti-emetics; e.g., Granisetron, Ondansetron)
• Silodosin
• Sirolimus
• Sotalol
• "statin" anticholesterol medications (e.g., Atorvastatin, Lovastatin, Simvastatin)
• Stiripentol
• Tacrolimus
• Tocilizumab
• Tolvaptan

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 Tykerb (Lapatinib). 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 Tykerb (Lapatinib).

Diarrhea: Tykerb (Lapatinib) can cause diarrhea that can lead to dehydration. Dehydration can cause many symptoms, including decreased urine production, dry and sticky mouth, sleepiness, dizziness, headache, thirst, and confusion. In some cases, dehydration can become a medical emergency. If you have diarrhea or any of these symptoms while taking Tykerb (Lapatinib), let your doctor know.

Heart effects: Tykerb (Lapatinib) can affect heart function. Your doctor will monitor you for these effects while you are taking Tykerb (Lapatinib). If heart problems occur, your doctor may stop Tykerb (Lapatinib) and restart it if your heart function improves.

Tykerb (Lapatinib) can also have an effect on the electrical activity of the heart called QT prolongation. If you experience an abnormal heartbeat, dizziness, palpitations, seizures, or fainting while taking Tykerb (Lapatinib), get immediate medical attention.

If you are at risk of complications due to QT prolongation (e.g., seniors, women, heart disease, abnormal heart rhythms, Stroke, Eating Disorders, Diabetes, a family history of sudden cardiac death) or are taking other medications that can cause QT prolongation (see the section "What medications can interact with Tykerb (Lapatinib)?"), discuss with your doctor how Tykerb (Lapatinib) may affect your medical condition, how your medical condition may affect the dosing and effectiveness of Tykerb (Lapatinib), and whether any special monitoring is needed.

Liver problems: Tykerb (Lapatinib) can cause reduced liver function and can cause liver failure, which can be fatal. Your doctor will monitor your liver function with blood tests while you are taking Tykerb (Lapatinib). If your liver function worsens, your doctor may stop Tykerb (Lapatinib).

If you have liver problems, discuss with your doctor how Tykerb (Lapatinib) may affect your medical condition, how your medical condition may affect the dosing and effectiveness of Tykerb (Lapatinib), and whether any special monitoring is needed.

If you experience symptoms of liver problems such as fatigue, feeling unwell, loss of appetite, nausea, yellowing of the skin or whites of the eyes, dark urine, pale stools, abdominal pain or swelling, and itchy skin, contact your doctor immediately.

Lung effects: Tykerb (Lapatinib) can cause lung problems. Your doctor will monitor you for these effects while you are taking Tykerb (Lapatinib). If you experience shortness of breath or difficulty breathing while taking Tykerb (Lapatinib), contact your doctor immediately. If lung problems occur, your doctor may need to stop Tykerb (Lapatinib).

Pregnancy: Tykerb (Lapatinib) should not be used during pregnancy unless the benefits outweigh the risks. If you become pregnant while taking Tykerb (Lapatinib), contact your doctor immediately. Women who may become pregnant should use contraception and avoid becoming pregnant while they are taking Tykerb (Lapatinib) and for at least 5 days after the last dose.

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

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