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 Granisetron. If you are concerned about side effects, discuss the risks and benefits of Granisetron with your doctor.

The following side effects have been reported by at least 1% of people taking Granisetron. 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.

• abdominal pain
• Constipation
• Diarrhea
• drowsiness
• headache
• unusual tiredness or weakness

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
• generalized pain
• signs of Anemia (low red blood cells; e.g., dizziness,  pale skin, unusual tiredness or weakness, shortness of breath)
• signs of heart problems such as palpitations (fast, pounding, or irregular heartbeat), chest pain, dizziness, or fainting
• shortness of breath
• skin rash, Hives, and itching

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

• signs of an allergic reaction such as feeling of Low Blood Pressure, skin lumps or hives, swelling of the mouth or airway
• symptoms of serotonin syndrome (e.g., agitation, confusion, mood changes, decreased coordination, hallucinations, fever, sweating, muscle shakes, loss of coordination)

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 Granisetron.

Do not take granisetron if you:

• are allergic to granisetron or any ingredients of the medication
• are taking the medication Apomorphine

There may be an interaction between granisetron and any of the following:

• Alfuzosin
• amantadine
• Amiodarone
• antihistamines (e.g., cetirizine, doxylamine, Diphenhydramine, Hydroxyzine, Loratadine)
• antipsychotics (e.g., Chlorpromazine, Clozapine, Haloperidol, Olanzapine, Quetiapine, Risperidone)
• apomorphine
• "azole" antifungals (e.g., itraconazole, ketoconazole, Voriconazole)
• Bromocriptine
• Buspirone
• chloral hydrate
• chloroquine
• Cyclobenzaprine
• Dabrafenib
• Dextromethorphan
• Disopyramide
• Domperidone
• Dronedarone
• ergot alkaloids (e.g., ergotamine, Dihydroergotamine)
• Famotidine
• Fingolimod
• Flecainide
• formoterol
• Galantamine
• hydroxychloroquine
• Indacaterol
• Indapamide
• Leuprolide
• lithium
• Loperamide
• lopinavir
• macrolide antibiotics (e.g., clarithromycin, erythromycin)
• Maprotiline
• Mefloquine
• Methadone
• mifepristone
• Mirtazapine
• monoamine oxidase inhibitors (M.O.S. e.g., Moclobemide, Rasagiline, Selegiline, Tranylcypromine)
• nefazodone
• Octreotide
• pentamidine
• Primaquine
• procainamide
• Propafenone
• protein kinase inhibitors (e.g., Bosutinib, Dasatinib, Pazopanib, Nilotinib, Sunitinib)
• quinidine
• quinine
• quinolone antibiotics (e.g., ciprofloxacin, Norfloxacin, Ofloxacin)
• ritonavir
• Romidepsin
• St. John's wort
• saquinavir
• selective serotonin reuptake inhibitors (SSRIs; e.g., Citalopram, Fluoxetine, Paroxetine, Sertraline)
• other serotonin antagonists (anti-emetic medications; e.g., Ondansetron, Palonosetron)
• serotonin/norepinephrine reuptake inhibitors (SNRIs; e.g., Desvenlafaxine, Duloxetine, Venlafaxine)
• Sotalol
• sulfamethoxazole
• Tacrolimus
• Tamoxifen
• Tapentadol
• Tetrabenazine
• Tramadol
• Trazodone
• Trimethoprim
• tricyclic antidepressants (e.g., Amitriptyline, Clomipramine, Desipramine, Trimipramine)
• ‘triptan' migraine medications (e.g., Eletriptan, Rizatriptan, Sumatriptan)
• Tryptophan
• Vardenafil
• Vemurafenib

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 Granisetron. 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 Granisetron.

Drowsiness/reduced alertness: There have been occasional reports of drowsiness by people who have taken granisetron. Avoid operating motor vehicles or doing other potentially hazardous activities until you determine the how Granisetron affects you.

Heart rhythm: Granisetron, like other medications in the same family, can cause changes to the normal rhythm of the heart, including an irregular heartbeat called QT prolongation. QT prolongation is a serious life-threatening condition that can cause fainting, seizures, and sudden death. If you are at risk for heart rhythm problems (e.g., people with heart failure, Angina, low potassium or magnesium levels), discuss with your doctor how Granisetron may affect your medical condition, how your medical condition may affect the dosing and effectiveness of Granisetron, and whether any special monitoring is needed.

Galactose intolerance/glucose malabsorption: Granisetron tablets are prepared with lactose. If you have lactose or galactose intolerance you should not take these medications.

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

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.

Serotonin Syndrome: Severe reactions are possible when granisetron is combined with other medications that act on serotonin, such as tricyclic antidepressants and serotonin reuptake inhibitors, medications used to treat Depression.

If you are taking antidepressants, discuss with your doctor how Granisetron may affect your medical condition, how your medical condition may affect the dosing and effectiveness of Granisetron, and whether any special monitoring is needed.

If you experience symptoms of a reaction, such as muscle rigidity and spasms, difficulty moving, changes in mental state including delirium and agitation, get immediate medical attention. Coma and death are possible.

Pregnancy: The safety of granisetron for use by pregnant women has not been established. Granisetron is not recommended for use during pregnancy. If you become pregnant while taking Granisetron, contact your doctor immediately.

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

Children: The safety and effectiveness of granisetron have not been established for children or adolescents under 18 years of age. Its use by this age group is not recommended.