alosetron vs ondansetron
PlainMeds reviewed this comparison against our methodology in August 2026. It places FDA and CMS record fields side by side, without recommending either medication.
Side-by-side comparison of alosetron and ondansetron. Data from FDA drug databases (Orange Book, NDC Directory, recalls, shortages) covering 20,000+ approved drugs, plus CMS pricing; see our methodology.
Lotronex
Zofran
Alosetron (Lotronex) is a medicine for women with severe diarrhea-predominant irritable bowel syndrome (IBS). It helps to reduce diarrhea and stomach pain.
Ondansetron is a medicine that helps prevent nausea and vomiting. It is often used during cancer treatment or after surgery.
Alosetron is used to treat severe diarrhea-predominant irritable bowel syndrome (IBS) in women. It is for women whose IBS symptoms have lasted for 6 months or longer. You should have already ruled out other possible causes of your symptoms. This medicine is only for you if other treatments have not worked well enough.
This medicine is used to prevent nausea and vomiting. It can help if you are getting chemotherapy for cancer. It also helps with nausea and vomiting after surgery or radiation.
Alosetron blocks a substance called serotonin in your gut. Serotonin can speed up bowel movements. By blocking serotonin, alosetron slows down your bowel and reduces diarrhea.
Ondansetron blocks a natural substance in your body called serotonin. Serotonin can cause nausea and vomiting. By blocking serotonin, ondansetron reduces these side effects.
- • Constipation
- • Abdominal discomfort and pain
- • Nausea
- • Gastrointestinal discomfort and pain
- • Headache
- • Feeling tired
- • Constipation
- • Diarrhea
- Diarrhoea 10
- Nausea 8
- Abdominal Pain 6
- Death 6
- Constipation 5
- Nausea 11,554
- Fatigue 8,199
- Diarrhoea 7,791
- Vomiting 7,326
- Death 4,872
Alosetron can cause serious gut problems, like ischemic colitis (reduced blood flow to the bowel) and severe constipation. These problems can lead to hospitalization, surgery, or even death. Stop taking alosetron right away if you get constipated or have symptoms of ischemic colitis, like bloody diarrhea or bad stomach pain. Call your doctor immediately.
Ondansetron can cause heart problems like a prolonged QT interval. If you have congenital long QT syndrome, you should not take this medicine. Ondansetron can also cause Serotonin Syndrome, especially if you are taking other medicines for depression or pain. Seek immediate medical attention if you experience chest pain.
It is not known if alosetron can harm your unborn baby. Talk to your doctor if you are pregnant or plan to become pregnant. It is also not known if alosetron passes into breast milk. Talk to your doctor about the best way to feed your baby if you take alosetron.
Talk to your doctor if you are pregnant or breastfeeding. It is not known if ondansetron will harm your unborn baby. Studies on the risk of birth defects are inconsistent.
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How to Read This alosetron vs ondansetron Comparison
alosetron is classified in the 5-HT3 Antagonist (IBS-D) drug class, while ondansetron sits within the 5-HT3 Receptor Antagonist (Antiemetic) class. Drugs from different classes work through distinct mechanisms, so a head-to-head comparison illustrates trade-offs rather than equivalence. Both drugs are prescription-only, so a licensed provider must authorize use.
Adverse event totals above are pulled from the FDA's Adverse Event Reporting System (FAERS). For these top-ranked reactions alone, alosetron has 35 submissions while ondansetron has 39,742. Those figures reflect cumulative reporting volume, not per-patient risk, so older, widely dispensed drugs typically look worse on count alone. No direct interaction between these two drugs is listed in our FDA-derived dataset, though co-prescription still warrants pharmacist review. Serious warnings, pregnancy guidance, and contraindications can differ even when indications overlap.
A table cannot represent individual circumstances. Data here is sourced from FDA Structured Product Labels (SPL) and FAERS, both of which update as manufacturers and clinicians submit new information. This registry does not provide medical, treatment, substitution, or medication-change directions for alosetron or ondansetron.
Registry boundary: This comparison displays source-record fields and does not provide individualized medical direction.