Ondansetron (Oral, Oromucosal)

Ondansetron is an oral medication prescribed by doctors to prevent the vomiting and nausea that often accompanies cancer treatments such as radiation and chemotherapy. Ondansetron can also be used to stop nausea symptoms in patients who have just had surgical procedures.


Ondansetron is very specific in that it only affects one nerve enzyme known as 5-HT3 receptor. This receptor is the nerve enzyme communicator that triggers nausea. By calming the stimulation that this nerve receptor has on the brain, Ondansetron effectively stops the patient from feeling sick, nauseated and eventually vomiting.

Nausea is an ill, queasy feeling that happens to many cancer patients and can lead to vomiting, dizziness, feeling faint or too rapid of a heart rhythm. Studies have shown that nausea and vomiting are caused in a certain portion of the brain that is triggered by use of chemotherapy drugs. Areas of the intestines, stomach, and esophagus may be triggered by chemotherapy into feeling sick or abnormal. Blocking this portion of the brain with drugs such as Ondansetron stops this trigger from happening, easing the nausea symptoms, which are the symptoms that are most dreaded by cancer patients.

Treating nausea and vomiting with Ondansetron and other medications like it allows the patient to get proper nutrition and also prevents dehydration from occurring. If patients cannot keep down fluids or take the medications they need, it directly affects the success of their chemotherapy or radiation treatment schedule. Ondansetron prevents and calms the nausea experienced so frequently during cancer treatment.

Ondansetron is sold under the following names for marketing purposes:

  • Zofran and Zofran ODT
  • Zuplenz

This medication can be taken in tablet or liquid solution form as well as a tablet that disintegrates in the mouth or a film strip for dissolving on the tongue. It is mostly given to patients prior to their chemotherapy treatment as it lasts for almost six hours to prevent the onset of nausea. If the patient already has nausea symptoms or has been vomiting, it may take longer for Ondansetron to take effect in the oral formulation, so it is also available in an injected format.

First used in 1990, Ondansetron is considered safe and effective by the WHO, who has it on their List of Essential Medicines. Another use for Ondansetron is for morning sickness or hyperemesis gravidarum, which is a severe form of morning sickness. There is a fetal risk associated with high dosage of Ondansetron, so it is only used in women who are pregnant if absolutely necessary and with caution on the amount and duration of the dosage.

Conditions Treated

  • Uremic pruritus
  • Cholestatic pruritus
  • Postoperative nausea and vomiting
  • Radiation induced nausea and vomiting
  • Chemotherapy induced nausea and vomiting
  • Severe Hyperemesis gravidarum

Type Of Medicine

  • Anti-nausea medication
  • Serotonin 5HT3 antagonist agent

Side Effects

Ondansetron may cause unwanted health effects by suppressing part of the nerve functions to alleviate nausea and stop a patient from vomiting. If you have the following health symptoms as the result of taking Ondansetron, alert your physician as they could be signs of serious underlying problems:

  • Confused demeanor
  • Dizzy
  • Trouble breathing
  • Rapid heart rhythm
  • Elevated body temperature
  • Headache
  • Weak muscles
  • Less volume or frequency of urination
  • Difficulty urinating or dribbling
  • Urinating is painful
  • Back, jaw or arm pain
  • Discomfort or pain in chest area
  • Convulsions
  • Coughing
  • Urine production or frequency is less than normal
  • Heavy, tight feeling in chest
  • Difficulty swallowing
  • Mouth dryness
  • Irregular heart rhythm, pounding or fast
  • Thirst has increased
  • Appetite has diminished
  • Bladder control is diminished or gone
  • Passing out
  • Mood swings
  • Pain or cramping in muscles
  • Vomiting
  • Nausea symptoms do not lessen
  • Breathing is labored or loud
  • Tingling, sleeping feet, lips or hands
  • Swollen, puffy eyes, lips, tongue or face
  • Rash or itching skin
  • Hives
  • Sweating
  • Body jerks or spasms
  • Fatigue
  • Weak muscles
  • Wheezing
  • Vision changes or is blurry
  • Lightheaded, passing out or dizzy when rising
  • Eye is immobile
  • Stopping of heart rhythm
  • Hoarse voice
  • Cannot move eyes
  • Spastic blinking of eyes
  • Hives on sex organs, eyes, face, tongue, lips, hands, feet, legs or throat
  • Breathing stops
  • Pulse or blood pressure is gone
  • Pounding heart rhythm
  • Breathing is very slow or irregular
  • Sticking tongue out involuntarily
  • Sweating
  • Difficulty speaking
  • Unconscious
  • Out of control twisting of the body, neck, legs or arms
  • Odd expressions on the face

Other side effects, while annoying, typically go away with time and continued use of the drug. You should still let your doctor know if you experience symptoms such as:

  • Anxious demeanor
  • Constipation
  • Mouth dryness
  • Overall ill or uncomfortable feeling
  • Rapid breathing or panting
  • Irritable mood
  • Restless, can't sit still
  • Shaking limbs
  • Insomnia
  • Difficulty speaking
  • Excessive saliva production
  • No balance
  • Jerking, stiff or trembling muscles
  • Shuffling when walking
  • Limbs feel stiff
  • Uncontrolled body twisting
  • Uncontrolled facial or neck movements
  • Warm feeling
  • Hiccups
  • Flushed neck, face, arms or upper chest
  • Skin redness
  • Hives or welts

Because every patient is different, you may have symptoms other than those listed here. Report any changes to your overall health, mood or wellbeing to your doctor while you are taking Ondansetron.


You should only take this medication exactly as your doctor has prescribed it for your condition. Do not increase the amount you are supposed to take or take it more often than prescribed. Do not take it for a longer period of time than you have been instructed to. Read and comprehend the patient information leaflet that arrives with your prescription and ask your physician or pharmacist if you have any questions or are unclear on any topic regarding the drug.

Patients who are prescribed the tablet that is to be allowed to dissolve on the tongue rather than swallowed should make sure their hands are dry prior to removing their dose from the packaging. Peel the foil backing rather than pushing the tablet out of it to remove to avoid breaking the tablet. Place the dissolving tablet on your tongue and swallow normally as it dissolves without swallowing the entire tablet. Do not drink water to swallow the tablet; allow your saliva to dissolve the medicine and swallow as you normally would.

Patients who are prescribed the film strip that dissolves on the tongue should also ensure that they have dry hands before removing the strip from the pouch it is packaged in. Place the film strip on your tongue immediately and allow it to dissolve naturally with your own saliva without chewing or swallowing it whole. Once dissolved, swallow with or without a glass of water as desired. If more than one strip of film is prescribed per dose amount, allow one strip to dissolve before taking the next until your dose amount is complete.

The amount of Ondansetron you are prescribed will depend on many factors including your overall health, your level of nausea with treatment, your age and your body mass. Your prescription should be followed exactly and any questions should be directed to your cancer care team. The following are general dosage amounts; keep in mind that yours may vary.

Adults and children 12 and up who are prescribed the disintegrating tablets, liquid solution or oral tablets will typically be given an initial 8 milligram initial dose to be taken at least a half hour prior to cancer treatment procedures. After the initial dose, another 8 milligram dose should be taken in 8 hours and repeated again every 12 hours for up to 2 days.

Children who are age 4 to 11 years old will have half this size of dose in the same period of time, a 4 milligram initial dose 30 minutes prior to treatment and repeated 4 to 8 hours after the initial dose. The 4 milligram dose will be repeated on an 8 hour basis for the next two days.

Children less than 4 years old may be prescribed this medicine in an amount determined by their team of cancer treatment professionals, who will take all health risks and efficiencies into consideration.

Tablet formats of Ondansetron in 24 milligram sizes are sometimes prescribed for adults and children over 12 to be taken 30 minutes prior to their cancer treatment. The tablet format may be prescribed for children younger than 12, which is up to their cancer care specialist to determine.

Adult patients who are receiving a radiation form of cancer treatment are typically prescribed an 8 milligram dose to be taken 1 to 2 hours prior to their treatment, repeated every 8 hours as appropriate. Children who are receiving radiation therapy must have their dosage determined by their cancer doctor or specialist.

Patients undergoing surgical procedures may also benefit from the effects of Ondansetron on their nausea symptoms. Adults will typically be given a 16 milligram dose prior to anesthesia to prevent them from becoming nauseated. Child surgical patients may or may not be given a dose of Ondansetron, which is up to their doctor to decide.

Adults and children who are older than 12 years of age who are prescribed the dissolving film strip format of Ondansetron will be instructed to take the 8 milligram strip of medication 30 minutes before their treatment is to begin. A second strip will be indicated for an 8 hour period after the initial dose and this will be repeated twice daily for a few days post-treatment. Children who are aged 4 to 11 will be given 4 milligram strips a half hour before treatment, repeated 8 hours after the first dose and again every eight hours for a few days post treatment. Children who have not yet reached age 4 may not be appropriate candidates for treatment with Ondansetron on their nausea symptoms. This will be decided by their physician when the time comes.

Three 8 milligram strips may be given to adult patients who experience more severe forms of nausea, for a total of 24 milligrams taken 30 minutes before their treatment. Children are not typically dosed with this quantity of Ondansetron, but their dose may be increased depending on their condition and what their doctor advises.

Dissolving film strip doses are also given to prevent nausea in radiation patients, with adults typically given 8 milligram amounts three times per day. Children under radiation treatment will only be given Ondansetron if deemed appropriate by their physician.

Adult surgical patients may have their nausea symptoms prevented with dissolving film strip versions of Ondansetron, which will be given in 16 milligram amounts (typically two 8 milligram strips), to be taken 1 hour prior to anesthesia. Children having surgery may have their dosage amount determined by their physician.

Missing a dose of Ondansetron is not advised but, if it does happen, take it as soon as you remember but do not double your dosage. If it is too close to your next dose by the time you remember, skip the missing dose in favor of resuming your normal dosing schedule.


If you have had sensitivity to any other medications in the past, including non-prescription drugs, let your physician know before you are given Ondansetron. You will also need to communicate any reactions you've had to animal dander, foods, dyes, perfumes or preservatives prior to your prescription.

Children younger than four years old have not been the subject of any study that provided data to ensure the safety and effectiveness of Ondansetron on this segment of the population. Use of this drug in young children is up to the physician in charge of their cancer treatment.

Age-related concerns with regard to use of Ondansetron on geriatric patients have not pointed to any unusually high risks or lower effectiveness with use of this drug.

Women who are pregnant are prescribed this drug when in need of relief from their severe nausea that is related to pregnancy. This condition is also known as hyperemesis gravidarum and it may be so severe that the mother's life is in danger. If so, Ondansetron is used in an emergency situation with extreme caution. Women are advised that there have been studies that have shown an increased risk of heart problems in children whose mothers have been treated with this medication. Use of this medication in pregnant women is only advised under extreme circumstances and need.

Studies on women who are breastfeeding have not provided any data to determine if the drug has been passed on to their infants via their breast milk. Women who are prescribed Ondansetron while they are breastfeeding may be advised to temporarily stop during their treatment.

Some medications work well together to provide an overall treatment to improve the health of patients. Other medications, however, may cause dangerous symptoms that can be life-threatening when combined. If you are taking Ondansetron, it is best to avoid other medications if possible including those found over-the-counter and at the health food store such as vitamin or herbal supplements and holistic treatments.

In particular, it is advised that you avoid the following medications and let your physician know if you are currently taking:

  • Amisulpride
  • Amifampridine
  • Bepridil
  • Apomorphine
  • Dronedarone
  • Cisapride
  • Ketoconazole
  • Fluconazole
  • Nelfinavir
  • Mesoridazine
  • Piperaquine
  • Pimozide
  • Saquinavir
  • Posaconazole
  • Terfenadine
  • Sparfloxacin
  • Ziprasidone
  • Thioridazine

The following drugs aren't recommended therapies to be taken in conjunction with Ondansetron, but may be necessary for your physical condition. Let your doctor know if you are taking:

  • Acecainide
  • Amiodarone
  • Alfuzosin
  • Amoxapine
  • Amitriptyline
  • Aripiprazole
  • Anagrelide
  • Asenapine
  • Arsenic Trioxide
  • Atazanavir
  • Astemizole
  • Azithromycin
  • Azimilide
  • Bretylium
  • Bedaquiline
  • Bupropion
  • Buprenorphine
  • Ceritinib
  • Buserelin
  • Chlorpromazine
  • Chloroquine
  • Citalopram
  • Ciprofloxacin
  • Clomipramine
  • Clarithromycin
  • Crizotinib
  • Conivaptan
  • Dabrafenib
  • Cyclobenzaprine
  • Dasatinib
  • Darunavir
  • Delamanid
  • Degarelix
  • Deslorelin
  • Desipramine
  • Dofetilide
  • Disopyramide
  • Domperidone
  • Dolasetron
  • Doxepin
  • Donepezil
  • Ebastine
  • Droperidol
  • Enflurane
  • Efavirenz
  • Erythromycin
  • Eribulin
  • Famotidine
  • Escitalopram
  • Fingolimod
  • Felbamate
  • Fluoxetine
  • Flecainide
  • Fosphenytoin
  • Foscarnet
  • Gatifloxacin
  • Galantamine
  • Gonadorelin
  • Gemifloxacin
  • Granisetron
  • Goserelin
  • Haloperidol
  • Halofantrine
  • Histrelin
  • Halothane
  • Hydroxychloroquine
  • Hydroquinidine
  • Ibutilide
  • Hydroxyzine
  • Iloperidone
  • Idelalisib
  • Isoflurane
  • Imipramine
  • Itraconazole
  • Isradipine
  • Lapatinib
  • Ivabradine
  • Levofloxacin
  • Leuprolide
  • Lumefantrine
  • Lopinavir
  • Methadone
  • Mefloquine
  • Metronidazole
  • Methylene Blue
  • Mirtazapine
  • Mifepristone
  • Moxifloxacin
  • Mizolastine
  • Nilotinib
  • Nafarelin
  • Nortriptyline
  • Norfloxacin
  • Ofloxacin
  • Octreotide
  • Oxycodone
  • Olanzapine
  • Panobinostat
  • Paliperidone
  • Pasireotide
  • Paroxetine
  • Pentamidine
  • Pazopanib
  • Perphenazine
  • Perflutren Lipid Microsphere
  • Pitolisant
  • Pimavanserin
  • Probucol
  • Pixantrone
  • Prochlorperazine
  • Procainamide
  • Propafenone
  • Promethazine
  • Quetiapine
  • Protriptyline
  • Quinine
  • Quinidine
  • Risperidone
  • Ranolazine
  • Salmeterol
  • Rilpivirine
  • Sertindole
  • Ritonavir
  • Sodium Phosphate
  • Sematilide
  • Sodium Phosphate, Monobasic
  • Sevoflurane
  • Sorafenib
  • Sodium Phosphate, Dibasic
  • Solifenacin
  • Sulpiride
  • Sotalol
  • Tacrolimus
  • Sunitinib
  • Tedisamil
  • Tamoxifen
  • Telithromycin
  • Telavancin
  • Tizanidine
  • Tetrabenazine
  • Toremifene
  • Tolterodine
  • Trifluoperazine
  • Trazodone
  • Triptorelin
  • Trimipramine
  • Vardenafil
  • Vandetanib
  • Venlafaxine
  • Vemurafenib
  • Voriconazole
  • Vinflunine
  • Zuclopenthixol
  • Vorinostat

Adverse health effects that patients may experience on Ondansetron could be amplified if taken with the following medications:

  • Tramadol
  • Cyclophosphamide

Avoid using tobacco products while you are on Ondansetron as it could cause adverse health effects as well as diminish the effectiveness of the drug. Seek help from your physician on tobacco cessation programs that can help you stop using tobacco products.

Consult your physician on whether you should or should not take Ondansetron with food, especially if you are given the dissolving strips or tablets. Certain foods may interact with Ondansetron and should be avoided. Any special dietary instructions will be given to you with your prescription.

Discuss the consumption of alcoholic beverages in conjunction with Ondansetron medication. Your doctor may alter your prescription or request that you limit your consumption during treatment if you regularly consume alcohol.

The following medical conditions may increase the risk of unwanted health effects with a prescription of Ondansetron. Make sure you or your doctor knows your full medical history, especially if it includes:

  • Hypersensitive health reactions to Ondansetron, Dolasetron, Alosetron, Granisetron or Palonosetron
  • Enlarged abdomen or bowel blockage
  • Congestive heart failure
  • Long QT syndrome or other heart problems
  • Low blood potassium levels
  • Low blood magnesium levels
  • Problems with heart rhythm
  • Disease of the liver
  • Phenylketonuria


If Ondansetron does not prove effective on your nausea and you are still feeling extremely ill and even vomiting, alert your physician right way. Continued nausea symptoms and vomiting can deplete your already exhausted system after cancer treatment and prove threatening to your health. It is imperative that you continue with your cancer treatment, which may have to be paused for you to recover if your nausea continues.

Patients who are taking Apomorphine, sold and labeled as Apokyn, will put their health at risk if they combine that drug with Ondansetron. Avoid using these medications together for any reason.

A severe hypersensitive reaction known as anaphylaxis may occur with use of Ondansetron. Symptoms such as breathing difficulty, swallowing difficulty, swelling in the mouth, hands or face and a skin rash with itching and a hoarse voice should be reported to your cancer treatment team right away.

Your heart rhythm health is at risk with use of Ondansetron and any changes to the intensity or speed should be reported to your physician to avoid any long-term health risks. Dizziness and fainting can be signs of a heart rhythm issue as well. If you have been diagnosed with Long QT syndrome or it runs in your family history, make sure you alert your physician to this fact prior to taking Ondansetron.

Dizziness is a regular effect reported by some patients after taking Ondansetron, so avoid dangerous activities, driving or operating machinery or tools until you are certain of your alertness and responsiveness. Protect yourself and others by not driving if you are dizzy or fatigued in any way.

Avoid over-the-counter remedies while you are taking Ondansetron as well as prescriptions, if possible. Some vitamins, herbal supplements and holistic remedies are known to interact with Ondansetron as well and should be avoided.


Retain the original packaging and patient information leaflet that your Ondansetron prescription arrives in for storage purposes. Keep the medication in the foil pouch until you are ready to take your dosage to protect it from moisture. Store this medication at room temperature and avoid exposure to excessive light, heat and moisture. Keep Ondansetron out of sight and reach of children and pets.

Dispose of any expired or unused medication safely under the instruction of your pharmacist or doctor, who will be aware of local ordinances on the disposal procedures for this medication.


Ondansetron is an anti-nausea medication that works by blocking the nerve cell communication enzyme known as 5-HT3 receptor. This enzyme prompts feelings of nausea and causes vomiting in patients who are undergoing chemotherapy cancer treatment and radiation therapy cancer treatment methods. Ondansetron is also effective in preventing nausea in patients who are about to have surgical procedures. In extreme circumstances, it is also prescribed to pregnant women who are suffering from a severe sickness known as hyperemesis gravidarum.

Safety has been proven in geriatric, adult and pediatric patients over four years of age for treatment with tablet forms, dissolving tablets, dissolving film strips and liquid solution forms of the drug. Dosage is determined by the physician in charge who will take age, body mass and medical history into consideration prior to prescribing a dose. It is unknown if this medication is safely taken by women who are breastfeeding with regard to passing forms of the drug onto their infants in their breast milk.

Dosage is typically indicated prior to the administration of chemotherapy or radiation from at least thirty minutes prior to the treatment. In surgical patients, it is recommended that the dosage be given at least one hour prior to the anesthetic being administered. Patients with severe liver impairment may not be able to take Ondansetron and should only be given 8 milligrams over a 24 hour period. Other patients are safely able to take up to 24 milligrams per day without concern.

Symptoms of anaphylaxis should be monitored for, as this hypersensitive reaction is at a higher risk with dosage of Ondansetron. Difficulty breathing or swallowing as well as a skin rash or itching should be reported in case they are signs of this condition. Patients are also at an increased risk of heart rhythm problems after taking Ondansetron and should report any dizziness or uneven heart rhythm to their physician to avoid any long-term health effects.

Avoid the use of other medications and tobacco products while you are taking Ondansetron so that the drug does not cause unwanted symptoms on your health or wellbeing. This drug has been known to interact poorly with many other drugs, even vitamin therapy, so be sure to disclose anything you are taking to your physician.

It is important to maintain good health while being treated for cancer in order to stay with the regimen and save your life. Treating nausea symptoms with Ondansetron so that you can nourish your body and hydrate yourself and stay well is important to your overall therapy. If this medication does not abate your nausea symptoms, let your doctor know right away so that another treatment can be sought.