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Warnings and Precautions With Ondansetron

Some Ondansetron Warnings and Precautions

Some ondansetron warnings and precautions to be aware of include:
  • Ondansetron can interact with certain medications (see Drug Interactions With Ondansetron).
  • Ondansetron is considered a pregnancy Category B medication. This means that ondansetron is probably safe for use during pregnancy. However, because ondansetron has not been studied in pregnant women, the full risks of using ondansetron during pregnancy are not known. Women who are pregnant should take ondansetron only if the benefits of taking ondansetron outweigh the risks to the developing baby. Be sure to discuss ondansetron's possible risks and benefits with your healthcare provider before using ondansetron during pregnancy (see Zofran During Pregnancy for more information).
  • It is not known if ondansetron can pass through breast milk. Therefore, if you are breastfeeding or plan to start breastfeeding, be sure to talk with your healthcare provider about this. He or she can decide whether taking ondansetron while nursing would be okay for your particular situation.
  • Ondansetron does not increase the activity or movement of the gastrointestinal tract and should not be used for this purpose. Using ondansetron after abdominal surgery or chemotherapy may mask the symptoms of an intestinal blockage (abdominal ileus). Talk to your healthcare provider right away if you are severely constipated or have abdominal cramping or bloating, as this may be a sign of intestinal blockage.
  • In very rare cases, ondansetron (especially the injectable version) can cause changes in the heart rhythm, including a specific type of arrhythmia called QT prolongation. People with long QT syndrome should not take ondansetron. People taking certain other medications, people with certain electrolyte balances, and people with heart disease may also be at an increased risk for QT prolongation with ondansetron.


  • Ondansetron orally disintegrating tablets (ODTs) contain phenylalanine (less than 0.03 mg per tablet). This is important for people with phenylketonuria, as they must limit their intake of phenylalanine.


  • The dose of ondansetron must be reduced in people will poor liver function. The maximum dose of ondansetron for people with severe liver problems is 8 mg per day.
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