Ondansetron: Uses, Side Effects, Interactions, Pictures, Warnings & Dosing

Uses

What is ondansetron used for?

Ondansetron is commonly used to prevent nausea and vomiting that can happen when using medicines for cancer, radiation therapy, anesthesia, and after some types of surgeries.

Ondansetron may also be used for other conditions as determined by your healthcare provider.

How does ondansetron work (mechanism of action)?

Ondansetron blocks a specific receptor in the gut (intestines) and brain called 5-HT₃ that normally causes nausea and vomiting when your body is exposed to certain substances, such as chemotherapy or anesthesia, or after surgery (especially on gut) or radiation treatment. By blocking this receptor, ondansetron reduces nausea and vomiting caused by chemotherapy, surgery/anesthesia, or radiation.

How is ondansetron supplied (dosage forms)?

Ondansetron is available in the following dosage forms that are taken by mouth.

4 mg and 8 mg orally disintegrating tablets
4 mg/5 mL oral solution
4 mg, 8 mg, and 24 mg oral tablets

Ondansetron is also available in injectable forms.

How should I store ondansetron?

Ondansetron should be stored at room temperature between 68 F to 77 F (20 C to 25 C). It can be exposed to temperatures between 59 F to 86 F (15 C to 30 C), for shorter periods of time, such as when transporting it. Store in a cool, dry place. Protect from light.

Side Effects

What are the most common side effects of ondansetron?

The most common side effects of ondansetron are listed below. Tell your healthcare provider if you have any of these side effects that bother you.

Headache
Tiredness
Constipation/diarrhea

There may be other side effects of ondansetron that are not listed here. Contact your healthcare provider if you think you are having a side effect of a medicine. In the U.S., you can report side effects to the FDA at www.fda.gov/medwatch or by calling 800-FDA-1088. In Canada, you can report side effects to Health Canada at www.health.gc.ca/medeffect or by calling 866-234-2345.

What are the serious side effects of ondansetron?

While less common, the most serious side effects of ondansetron are described below, along with what to do if they happen.

Severe Allergic Reactions. Ondansetron may cause allergic reactions, which can be serious. Stop taking ondansetron and get help right away if you have any of the following symptoms of a serious allergic reaction.

Breathing problems or wheezing
Racing heart
Fever or general ill feeling
Swollen lymph nodes
Swelling of the face, lips, mouth, tongue, or throat
Trouble swallowing or throat tightness
Itching, skin rash, or pale red bumps on the skin called hives
Nausea or vomiting
Dizziness, feeling lightheaded, or fainting
Stomach cramps
Joint pain

Heart Rhythm Changes. Ondansetron may cause a rare, dangerous heart rhythm problem called QT prolongation and torsade de pointes. Some people have a higher risk of this, including people who are older, have other people in their family who have had these conditions, have low potassium or magnesium levels, or who take some medicines for other heart rhythm problems. Tell your healthcare provider right away if you faint or have changes in your heart rate or rhythm, such as a fast or skipping heartbeat.

Other Heart Problems. Ondansetron can cause poor blood flow to the heart, which is called myocardial ischemia. This can result in chest pain. Myocardial ischemia is more likely if you are given the IV form of ondansetron, or if you have existing heart disease. Do not take ondansetron if you have had a recent heart attack without talking to your healthcare provider. Get emergency help if you have any of the following symptoms of a heart attack.

Chest pain or pressure
Fast or abnormal heartbeat
Trouble breathing
Pain in your back, jaw, throat, or arm
Sweating, upset stomach, vomiting, or dizziness

Serotonin Syndrome. Serotonin syndrome is when there is too much of a substance called serotonin in your body. Ondansetron can cause serotonin syndrome when it is taken alone or with other medicines that affect serotonin (see Interactions). This condition can be life-threatening. Get emergency help if you have any of the following symptoms of serotonin syndrome.

Sweating, fever, or flushing
Confusion
Feeling agitated or restless
Seeing or hearing unusual things
Dizziness
Fast or racing heartbeat
Nausea, vomiting, or diarrhea
Muscle twitching, stiffness, or tremor
Seizures

Warnings & Precautions

Who should not use ondansetron?

Allergies to Ingredients. People who are allergic to any of the following should not take ondansetron.

Ondansetron
Any of the ingredients in the specific product dispensed

Your pharmacist can tell you all of the ingredients in the specific ondansetron products they stock.

Drug Interactions. Ondansetron should not be used while you are using certain other medicines. Before using ondansetron, tell your healthcare provider about any prescription or over-the-counter (OTC) medicines, vitamins/minerals, herbal products, and other supplements you are using. See the Interactions section for more details

What should I know about ondansetron before using it?

Do not take ondansetron unless it has been prescribed to you by a healthcare provider. Take it as prescribed.

Do not share ondansetron with other people, even if they have the same condition as you. It may harm them.

Keep ondansetron out of the reach of children.

What should I tell my healthcare provider before using ondansetron?

Tell your healthcare provider about all of your health conditions and any prescription or over-the-counter (OTC) medicines, vitamins/minerals, herbal products, and other supplements you are using. This will help them determine if ondansetron is right for you.

In particular, make sure that you discuss any of the following.

Current and Past Health Conditions. Tell your healthcare provider if you have any of the following.

Long QT syndrome
Electrolyte problems (such as low potassium or low magnesium)
Congestive heart failure
Other heart rhythm problems (slow heartbeat/bradycardia)

Abdominal Surgery. Tell your healthcare provider if you have had recent surgery on your gut (stomach or intestines). In this case, as ondansetron prevents nausea and vomiting, it may be more difficult to determine if you are having complications from your surgery, such as any blockage, for example.

Pregnancy. It is not known if or how ondansetron could affect pregnancy or harm an unborn baby. Tell your healthcare provider if you are or plan to become pregnant.

Breastfeeding. It is not known if ondansetron passes into breast milk. Tell your healthcare provider if you are breastfeeding or plan to breastfeed.

Interactions

Does ondansetron interact with foods or drinks?

There are no known interactions between ondansetron and foods or drinks.

It is unknown if drinking alcohol will affect ondansetron.

Does ondansetron interact with other medicines (drug interactions)?

Always tell your healthcare provider about any prescription or over-the-counter (OTC) medicines, vitamins/minerals, herbal products, and other supplements you are using.

In particular, make sure that you discuss if you are using any of the following before using ondansetron.

Medicines [within the past 2 weeks] that can cause QT prolongation, which is a potentially dangerous heart rhythm problem
A selective serotonin reuptake inhibitor (SSRI), which is a medicine commonly used for anxiety and depression
A serotonin norepinephrine reuptake inhibitor (SNRI), which is a medicine commonly used for anxiety and depression
A type of medicine called a triptan, such as sumatriptan (Imitrex and others), eletriptan (Relpax), and others, which is commonly used to treat migraines
Apomorphine (Apokyn), which is a medicine commonly used for Parkinson’s disease
Tramadol, which is a medicine used for pain

This may not be a complete list of medicines that can interact with ondansetron. Always check with your healthcare provider.

Does Ondansetron interact with other drugs you are taking?

Enter your medication into the WebMD interaction checker

Overdose/Missed Dose

What should I do if I accidentally use too much ondansetron?

If you or someone else has used too much ondansetron, get medical help right away, call 911, or contact a Poison Control center at 800-222-1222.

What should I do if I miss a dose of ondansetron?

If you miss a dose, take it as soon as you remember. If it is almost time for your next dose, skip the missed dose and only take the next dose. Do not take double or extra doses.

If you are being given ondansetron injections, be sure to make it to your appointment on time, as prevention of nausea and vomiting that occurs after radiation, chemotherapy, or surgery, requires that you are given your ondansetron at the right time.