Ondansetron and Amitriptyline: Interaction Details
AI-assisted, pharmacist-reviewed · AI content regenerated Jul 11, 2026 · Source data updated Jul 2, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature
Amitriptyline
Ondansetron
No brand names on record
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.
Both of these medicines can affect your body in similar ways, so using them together can add up. Amitriptyline (Elavil) is an older antidepressant, and ondansetron is often used to prevent nausea. Both can raise serotonin levels and both can affect your heart's rhythm (something called QT prolongation).
Taken together, there is a possible increased risk of two things: serotonin syndrome (symptoms like agitation, sweating, shivering, fast heartbeat, or muscle twitching) and heart rhythm changes. This is mostly a theoretical concern, not something proven to happen often. The good news is your care team can manage this by watching you more closely, so please talk with your pharmacist or doctor rather than changing anything on your own.
Effect: Additive risk of serotonin syndrome and QT-interval prolongation with concomitant amitriptyline (a serotonergic TCA and known QT-prolonging agent) and ondansetron (a 5-HT3 antagonist with QT-prolonging potential).
Mechanism: Pharmacodynamic, not PK. Additive serotonergic activity plus additive QT prolongation. Neither is a prodrug relevant to this effect.
- Direction: increased combined risk (additive)
- Evidence: theoretical; serotonin syndrome reported mainly in infusion/PACU settings
- Onset: unspecified
- Management: if coadministration is necessary, monitor ECG and for signs of serotonin syndrome; correct electrolytes; discontinue ondansetron and give supportive care if serotonin syndrome emerges.
What happens
An increased risk of serotonin syndrome and QT interval prolongation
Interaction Deep Dive
Taking ondansetron together with an agent that has both serotonergic and QT-interval prolonging properties can raise the likelihood of serotonin syndrome as well as QT-interval prolongation. Cases of serotonin syndrome have been documented when 5-hydroxytryptamine-3 antagonists are given alongside serotonergic medications, occurring chiefly within infusion centers or post-anesthesia care units. Should the two need to be given together, monitor the ECG and watch for signs of serotonin syndrome developing. If serotonin syndrome symptoms appear, stop ondansetron and begin supportive care1.
Why it happens (mechanism)
Additive serotonergic effects; additive QT interval prolongation
How to manage this interaction
Keep taking both medicines as prescribed unless your care team tells you otherwise. This combination can be used with appropriate monitoring.
Here is what your team may do and what you can do:
- Your team may check an ECG to watch your heart rhythm, especially if you have other risk factors.
- They may watch for early signs of serotonin syndrome (agitation, confusion, sweating, shivering, fast heartbeat, muscle twitching or stiffness).
- Doses may be adjusted and individualized by your care team, or an alternative anti-nausea option may be considered.
- Seek prompt medical help if you feel very restless, feverish, or notice a racing or irregular heartbeat, fainting, or dizziness.
Raise any concerns with your pharmacist or prescriber before making changes.
Management is individual — confirm any change with your pharmacist or prescriber.
Common questions
Can I take Ondansetron and Amitriptyline together?
Using amitriptyline and ondansetron together can add up to a higher risk of serotonin syndrome and heart rhythm changes, so your care team may monitor you more closely; keep taking both as prescribed and report symptoms like agitation, sweating, or a racing heartbeat. Always confirm with your pharmacist or prescriber before making any change.
How serious is the Ondansetron and Amitriptyline 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 is the Ondansetron and Amitriptyline interaction managed?
Keep taking both medicines as prescribed unless your care team tells you otherwise. This combination can be used with appropriate monitoring. Here is what your team may do and what you can do: Your team may check an ECG to watch your heart rhythm, especially if you have other risk factors. They may watch for early signs of serotonin syndrome (agitation, confusion, sweating, shivering, fast heartbe… Management is individual — always follow your own care team's guidance.
How strong is the evidence for this interaction?
The evidence is graded "theoretical". Predicted from the drugs' pharmacology; not yet confirmed in people.
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 Amitriptyline 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: Ondansetron HCl oral tablets, ondansetron HCl oral tablets. Eywa Pharma Inc (per DailyMed), Princeton, NJ, 2020. DailyMed
Keep reading about Amitriptyline
Keep reading about Ondansetron
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