Terfenadine 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
Terfenadine
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.
These two medicines should not be taken together. Amitriptyline (Elavil) is an older antidepressant, and terfenadine is an older allergy medicine. Both can affect the timing of your heart's electrical rhythm, something doctors call the QT interval. When you take both, that effect can add up.
If the QT interval gets too long, it can lead to a dangerous, irregular heartbeat. The good news is this is easy to avoid. Your care team almost always has a safer allergy option they can choose instead. Please talk with your pharmacist or doctor before taking these together, and don't stop anything on your own.
Contraindicated combination. Both agents independently prolong the QT interval, so concomitant use produces additive QTc prolongation and raises the risk of torsades de pointes and serious ventricular arrhythmias.
- Mechanism: additive cardiac repolarization delay (pharmacodynamic, not a prodrug interaction).
- Direction: increased combined QT-prolonging effect.
- Evidence: theoretical, but severity is rated contraindicated given the arrhythmia risk.
- Onset: unspecified.
Management: avoid co-prescribing. Select a non-QT-prolonging antihistamine alternative. If any QT-prolonging agent is unavoidable, correct electrolytes (K+, Mg2+) and monitor ECG.
What happens
An increased risk of QT interval prolongation
Interaction Deep Dive
Using terfenadine together with medications that prolong the QT interval is contraindicated, since giving them at the same time can heighten the likelihood of QT prolongation and dangerous ventricular arrhythmias1.
Why it happens (mechanism)
Additive QT interval prolongation
How to manage this interaction
This pairing is generally avoided. Because both drugs can lengthen the QT interval, the usual approach is to not use them together.
- Keep taking your prescribed medicines as directed until you speak with your care team. Do not stop or change anything on your own.
- Your prescriber can often switch you to a safer allergy medicine that does not affect heart rhythm.
- If both are truly needed, your team may check an ECG and your electrolyte levels and monitor you more closely.
Tell your pharmacist or doctor that you have been prescribed both amitriptyline and terfenadine so they can review the combination.
Management is individual — confirm any change with your pharmacist or prescriber.
Common questions
Can I take Terfenadine and Amitriptyline together?
Amitriptyline and terfenadine both prolong the QT interval, and using them together is contraindicated because of the added risk of dangerous heart rhythms. Ask your pharmacist or doctor about a safer alternative before combining them. Always confirm with your pharmacist or prescriber before making any change.
How serious is the Terfenadine and Amitriptyline interaction?
It is rated contraindicated. These should generally not be used together.
How quickly could this interaction happen?
The documented onset is "unspecified". The timing of this interaction is not well characterized.
How is the Terfenadine and Amitriptyline interaction managed?
This pairing is generally avoided. Because both drugs can lengthen the QT interval, the usual approach is to not use them together. Keep taking your prescribed medicines as directed until you speak with your care team. Do not stop or change anything on your own. Your prescriber can often switch you to a safer allergy medicine that does not affect heart rhythm. If both are truly needed, your team m… 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 Terfenadine 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: Seldane(R), terfenadine. Marion Merrell Dow, Kansas City, MO, 1996.
Keep reading about Amitriptyline
Keep reading about Terfenadine
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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