Last Updated December 20th, 2021

An overview

Ondansetron is the generic form of Zofran, which is an antiemetic drug.  Antiemetics are known to belong to a class of drug.  A group of drugs that work similarly is considered a class of drugs.  This drug is used to relieve symptoms of nausea and vomiting caused by various factors such as chemotherapy, radiation therapy, as well as surgery.

The main function of this drug is to block the actions of an enzyme called serotonin and is classified as 5-HT3 receptor antagonists.  Serotonin is a neurotransmitter that is known to cause nausea and vomiting.  When this neurotransmitter is blocked by the antiemetic agent, it is able to mask the effect of cancer-treating drugs and helps to relieve symptoms of nausea and vomiting.

Ondansetron is generally administered orally and is available in tablet form, oral disintegrating tablets, solutions, as well as available in injection form, which needs to be administered intravenously.

Types of antiemetic drugs

Antiemetic drugs are formulated to relieve symptoms of nausea and vomiting.  Nausea and vomiting can be caused due to various factors.  Some of the commonly used antiemetics for different types of nausea and vomiting are discussed below.

Antiemetic drugs for motion sickness

Motion sickness is a medical condition where a person may experience symptoms of dizziness, fatigue, loss of appetite, vertigo, as well as nausea and vomiting.  The person may experience these symptoms while traveling by car, train, airplanes, as well as by boat.  It may affect anybody, but generally affects children and pregnant women.  Since the inner ear plays an important role in causing motion sickness, these antiemetics makes the inner ear to be less sensitive to the motion of the head and helps in reducing the symptoms of nausea and vomiting.  Some of the commonly used antiemetics for motion sickness include dimenhydrinate, diphenhydramine, meclizine, as well as promethazine.  It should be noted that all these medications have certain side effects associated with them and this need to be discussed and understood with a healthcare provider before using them.

Antiemetic drugs for surgery

Complaining of nausea and vomiting after surgery is common and this is due to the anesthesia which the patient is subjected to before the surgery.  Since anesthesia can cause symptoms of nausea and vomiting, doctors choose to treat them with certain drugs such as dopamine receptor blockers, corticosteroids, as well as serotonin receptor blockers.  Some of the commonly used antiemetic for surgery related nausea and vomiting include dexamethasone, droperidol, granisetron, metoclopramide, as well as ondansetron.

Antiemetic drugs for patients undergoing chemotherapy

Chemotherapy treatment involves using one or more drugs to treat cancer.  A combination of drugs may be used in this case that is intended to treat cancer, prolong the life expectancy, as well as to reduce symptoms associated with cancer.  It is quite common that these anticancer drugs called chemotherapy are known to cause symptoms of nausea and vomiting.  This would make it difficult for the patient to consume any food due to the feeling of constant nausea.  Due to this reason, doctors generally prescribe antiemetics before and after the dosage of chemotherapy so as to provide relief from nausea and vomiting.  Some of the class of drugs used include dopamine receptor blockers, serotonin receptor blockers, NK1 receptor blockers, as well as corticosteroids.  Some of the commonly used drugs include aprepitant, dexamethasone, dolasetron, granisetron, ondansetron, palonosetron, prochlorperazine, and rolapitant.  Patients who do not respond with these drugs may also be prescribed with cannabinoids from medical marijuana as well as dronabinol, which is a prescription drug.

Antiemetics for stomach flu

Gastroenteritis which is generally called stomach flu is known to cause symptoms of nausea and vomiting.  Generally, the stomach flu would subside following vomiting and when the stomach clears up.  In certain cases, there may be cyclic vomiting, which can lead to dehydration and this can cause other complications.  Your doctor would generally prescribe certain over-the-counter medications to treat these symptoms.  Some of the commonly used medications include sodium citrate, phosphoric acid, as well as bismuth subsalicylate that can provide a soothing effect to the stomach as well as relieve the symptoms of nausea and vomiting.

Antiemetics for pregnant women

Symptoms of nausea and vomiting may be experienced by women during pregnancy.  Morning sickness is a common phenomenon when pregnant women feel nauseated and hardly feel like eating anything.  These symptoms are common and generally dissipate over time.  Antiemetics may be prescribed during a severe case such as hyperemesis gravidarum where you may experience symptoms of severe nausea and vomiting leading to electrolyte imbalance as well as dizzy feeling.  Since the medications may affect the fetus, these antiemetics are rarely prescribed and include dimenhydrinate, prochlorperazine, promethazine, and vitamin B-6.  Using cannabinoids should be strictly avoided during pregnancy since they may affect the fetus.

Side effects of antiemetics

As discussed earlier, there are various types of antiemetics used to relieve the symptoms of nausea and vomiting that may be caused due to several factors.  Since different antiemetics cause different side effects, it would be helpful if the side effects associated with a particular antiemetic is known in advance.  Some of the common side effects associated with these antiemetics are discussed below.


These are obtained from marijuana and should never be used by pregnant women.  Some of the common side effects include altered mental state as well as dizziness.


Steroids are known to increase the blood sugar levels and people suffering from diabetes should use them with caution.  Some of the additional symptoms related to corticosteroids include increased hunger and thirst, indigestion, as well as acne.

Serotonin receptor blockers

Commonly used during chemotherapy treatments.  They generally cause constipation, fatigue, as well as dry mouth.


Generally used to treat motion sickness and morning sickness in pregnant women.  These antihistamines are known to cause dry mouth, dry nostrils, as well as increased sleepiness.  It is considered to be highly dangerous to drive or operate machinery after using these medications.


Generally used to treat symptoms of stomach flu.  They are known to cause your stool to be black in color.  They can also cause a change in the color of your tongue.

NK1 receptor blockers

These antiemetics are prescribed along with chemotherapy drugs to relieve symptoms of nausea and vomiting.  They are known to cause heartburn, dry mouth, as well as reduced urine output.

Dopamine receptor blockers

These antiemetics are known to cause side effects of muscle spasm, constipation, restlessness, fatigue, as well as dry mouth.


As we have discussed the side effects associated with these medications, there is also the possibility that these medications may even cause complications.  Some of the complications associated with these medications include weakness in the muscles, convulsions, spasms, alteration in heartbeats such as palpitations, slurred speech, hearing loss, hallucinations, confusion, drowsiness, as well as worsening of nausea or vomiting.  These complications generally arise when antiemetics are combined with other drugs or if the person is allergic to a particular drug.  It is always best to discuss with your healthcare provider about the allergies and know which medications to avoid.  Certain medications such as arthritis medication, diabetes medication, blood thinners, cold medications, as well as medicines for gout can cause similar side effects.  Combining these medications with antiemetics can make the situation worse and lead to complications.

Natural antiemetics

If you would like to avoid these side effects and complications associated with these drugs, you can choose natural antiemetics that are safe and free from side effects.  A very well known natural antiemetic is the ginger root.  Ginger root can be consumed in the form of tea which can reduce the symptoms of nausea and vomiting.  It is believed that lemons are also known to provide antiemetic effects when the skin of the lemon is scraped and the aroma is inhaled.  It is known to provide relief from nausea associated with motion sickness.  More studies are required to substantiate these claims, but the initial research showed promising results.  Essential oils are also known to provide antiemetic effects.  Some of these essential oils include peppermint oil, ginger oil, spearmint oil, as well as lemon oil.  These essential oils can be inhaled to get relief from nausea and vomiting.  It can also be added to a diffuser to inhale the vapor.  It is important to note that these natural antiemetics need to be used only under medical supervision.

Interactions of ondansetron

Certain medications are known to interact with ondansetron and are known to cause some serious side effects.  Some of these medications include:


Taking apomorphine in combination with ondansetron can reduce blood pressure levels and cause hypotension.  This may cause a person to become jittery and lose consciousness.

Fluoxetine and paroxetine

Consuming these medications with ondansetron can affect serotonin levels.  Since serotonin is a neurotransmitter hormone, it can lead to various other complications when the levels are altered.

Phenytoin or carbamazepine

These are anti-seizure medications and can make ondansetron less effective.

Rifampin and rifabutin

These medications are used to treat tuberculosis and are known to make ondansetron ineffective.

Warnings with respect to ondansetron

People suffering from heart arrhythmias

Studies have claimed that these drugs are known to increase the risk of arrhythmias, so it is important to avoid this drug if you are suffering from heart problems such as heart failure or congenital long QT syndrome.

People suffering from phenylketonuria

Phenylketonuria is a rare condition which affects the metabolism of phenylalanine, which is an amino acid.  It is advised that people suffering from this condition should strictly avoid ondansetron, as it can worsen the condition.

Pregnant women

There are very few human studies conducted and further studies are required to determine the effect of ondansetron on the fetus when consumed by pregnant women.  Animal studies have shown no serious effects, but the more precise human study is required to determine the effects.

For women who are breastfeeding

Studies have claimed that ondansetron can mix with breast milk and cause some side effects to the child.  It is recommended to consult your doctor to know if it is safe to take this medication when breastfeeding.

Older adults

It has been found that the kidneys in older adults may not work as effectively as it should be and there is a high risk that the drug may remain in the system for a prolonged period of time leading to side effects.


Effects of this medication have not been tested on children below four years of age.  It is advised that the medication should be kept out of reach of children in order to avoid complications.

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