What are ondansetron hydrochloride (Zofran) side effects?

Signs of ondansetron allergic reactions: difficulty breathing, hives (rash on your body), swelling of the face, lips, tongue, or throat—If you experience any of these symptoms, please call 911 or seek emergency medical care at the nearest emergency room (ER). 

Call your doctor immediately if you experience any of the following signs and symptoms:

• Serotonin syndrome or high level of serotonin in your body: fever, sweating, fast/pounding heart rate, nausea and vomiting, agitation, hallucinations, loss of coordination, fainting, diarrhea
• Stomach pain, severe constipation
• Headache with chest pain
• Severe dizziness; fast, pounding heart rate
• Jaundice (yellowing of the skin or eyes)
• Blurred vision or sudden vision loss that can last from minutes to several hours 

Common side effects of ondansetron:

• Headache
• Drowsiness
• Tiredness
• Diarrhea or constipation

Less common side effects of ondansetron:

• Decrease in frequency/amount of urination
• Difficult urination
• Painful urination

Ondansetron overdose: Go to the nearest emergency room or call the Poison Help Line at 1-800-222-1222. You can find more information at your local poison control center or at www.poisonhelp.org/help

Ondansetron overdose symptoms: 

• Sudden loss of vision
• Lightheadedness
• Dizziness
• Fainting
• Severe constipation

The above list on this site may not include all the possible side effects of ondansetron hydrochloride. Speak to your doctor or pharmacist at your local pharmacy if you have persistent side effects or any side effects that are not listed above. You can also report side effects to the Food and Drug Administration (FDA) at 1-800-FDA-1088.

Source: FDA