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Ondansetron is a pharmacy drug classified in the family of drugs known as serotonin 5-HT3 receptor antagonists. Ondansetron is effective, in many patients, as a serotonin blocker, which can help to stave off negative side effects such as vomiting and nausea that often present with chemotherapy and radiation treatment.


Ondansetron is typically taken orally, as prescribed by your physician. Ondansetron tablets are designed to dissolve on top of the tongue. Use only your body's natural saliva to dissolve, then swallow. Do not take this medication with water as this may exacerbate your chance of developing a headache side effect. Chemotherapy and radiation applications have different dosages and scheduling; talk to your physician and ensure that you are aware of how to take this medicine properly.


Ondansetron can cause certain side effects. At your initial consultation with your physician, ask her or him to explain how side effects might affect you and know what to watch for. If you experience a side effect that persist or get worse, see your physician right away. Common side effects seen with ondansetron are as follows:

  • Dizziness
  • Lightheadedness
  • Drowsiness
  • Headaches
  • Tired Feeling
  • Constipation

Potentially More Severe Side Effects:

Some patients may experience side effects that could be potentially severe. If you experience anything that feels severe, or any of the side effects listed below, see your physician at once. If your physician is unavailable then go to a medical treatment facility for care right away. Never underestimate the potential for severe side effects to cause harm; anything severe requires prompt medical attention. For your convenience a partial list of some potentially severe side effects is provided below.

  • Chest Pain
  • Irregular Heartbeat
  • Accelerated Heartbeat
  • Slow Heartbeat
  • Fainting
  • Severe Dizziness
  • Stiffness
  • Muscle Spasm
  • Stomach Pain
  • Temporary Loss of Vision
  • Blurred Vision
  • Other Vision Changes and/or Anomalies

Allergic Reaction Warning:

Some patients might experience an allergic reaction. If you experience anything that feels like it could be an allergic reaction, or experience any of the symptoms listed below, get medical help immediately.

  • Swelling of the Face, Throat or Tongue
  • Difficulty Breathing
  • Rash
  • Extreme Dizziness

WARNING: Ask your physician about serotonin syndrome, a potentially dangerous condition that can result from dramatic serotonin increases. Serotonin syndrome may play a part in the development of certain symptoms listed below, all of which require immediate medical treatment.

  • Severe Nausea
  • Severe Vomiting
  • Severe Diarrhea
  • Muscle Twitching
  • Restlessness
  • Unexplained Fever
  • Agitation
  • Accelerated Heartbeat
  • Hallucinations
  • Extreme Dizziness
  • Loss of Coordination


Never take ondansetron without approval from your physician. If considering the use of this drug, see your physician for a complete medical screening and consultation.

Ask your physician about the many possible contraindications relevant to you and your condition.

Ondansetron may be contraindicated for any of the conditions listed below. Ask your doctor for more information if any apply to you.

  • Severe Liver Disease
  • Extrapyramidal Reaction
  • Low Level of Magnesium in Blood
  • Low Level of Potassium in Blood
  • Neuroleptic Malignant Syndrome
  • Serotonin Syndrome
  • Slow Heartbeat
  • Chronic Heart Failure
  • Rapid Heartbeat
  • Torsades De Pointes
  • Prolonged QT Interval on EKG
  • Abnormal EKG with QT Changes
  • "It is rare to find health professionals who are so willing to educate the patient on what they need to know."

    Clair C. | West Hollywood, CA