Ondansetron and Loperamide: Interaction Details
AI-assisted, pharmacist-reviewed · Source data updated Aug 8, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature
Ondansetron
No brand names on recordLoperamide
How we grade severity & evidence
Severity levels
- Contraindicated: These should generally not be used together.
- Major: Potentially serious — often needs a change or close monitoring.
- Moderate: Can be significant — usually manageable with monitoring.
- Minor: Usually limited clinical impact.
Evidence grades
- Established: Well documented — supported by controlled studies or strong clinical data.
- Probable: Good supporting evidence, though not definitively proven.
- Suspected: Some evidence suggests this interaction, but it is not well established.
- Possible: Limited or conflicting evidence; the interaction may occur.
- Theoretical: Predicted from the drugs' pharmacology; not yet confirmed in people.
Ratings come from the documented interaction literature and are reviewed by a pharmacist. They describe the documented risk of the combination, not what will necessarily happen to you — your dose, timing, and health picture all matter.
What happens
An increased risk of QT interval prolongation, which may increase risk of cardiotoxicity (torsade de pointes, cardiac arrest)
Interaction Deep Dive
Avoid concomitant use of loperamide with other drugs or herbal products that are known to prolong the QT interval. Cases of syncope and ventricular tachycardia have been reported in adult patients receiving the recommended dosage of loperamide. Cases of prolongation of the QT interval, torsade de pointes, other ventricular arrhythmias, cardiac arrest, some resulting in death, have been reported in adults with use of higher than recommended doses of loperamide1.
Why it happens (mechanism)
Additive QT interval prolongation
Literature reports
1 report — tap to read
a) Cases of syncope and ventricular tachycardia have been reported in adult patients receiving the recommended dosage of loperamide. Some of these patients were taking other drugs or had other risk factors that may have increased their risk of cardiac adverse reactions. Cases of prolongation of the QT interval, torsade de pointes, other ventricular arrhythmias, cardiac arrest, some resulting in death, have been reported in adults with use of higher than recommended doses per day of loperamide 1.
Common questions
Can I take Ondansetron and Loperamide together?
An increased risk of QT interval prolongation, which may increase risk of cardiotoxicity (torsade de pointes, cardiac arrest) Always confirm with your pharmacist or prescriber before making any change.
How serious is the Ondansetron and Loperamide interaction?
It is rated major. Potentially serious — often needs a change or close monitoring.
How quickly could this interaction happen?
The documented onset is "unspecified". The timing of this interaction is not well characterized.
How strong is the evidence for this interaction?
The evidence is graded "probable". Good supporting evidence, though not definitively proven.
From our Q&A
Real reader questions about these medications, each personally answered by our pharmacist:
Questions for your pharmacist
- Does my dose of Ondansetron or Loperamide need adjusting while I take them together?
- What symptoms should prompt me to call you or my prescriber right away?
- Does the timing of my doses matter for this combination?
- Is there a safer alternative to one of these medications for me?
References (1)
- Product Information: Loperamide hydrochloride oral capsules, loperamide hydrochloride oral capsules. Mylan Pharmaceuticals Inc (per DailyMed), Morgantown, WV, 2022. DailyMed
Keep reading about Ondansetron
Keep reading about Loperamide
These medications also interact with supplements
Prescription drugs aren't the whole picture — herbal and dietary supplements can interact with them too. From the evidence-graded Natural Medicines database:
major · moderate · minor — check everything you take with our drug–supplement interaction checker.
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