Relugolix and Terfenadine: 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
Relugolix
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.
Both of these medicines can affect the timing of your heartbeat. Doctors call this QT prolongation, which is a small delay in how your heart's electrical system resets between beats. Relugolix (Orgovyx) can do this, and so can terfenadine, an older allergy medicine. When two medicines that both do this are taken together, the effect can add up and, in rare cases, lead to a dangerous heart rhythm.
Because of this, using these two together is not recommended at all. The good news is this is very manageable. Please don't stop either medicine on your own, just talk with your doctor or pharmacist so they can pick a safer option for you.
Effect: Additive risk of QT interval prolongation and potential for serious ventricular arrhythmias (including torsades de pointes).
Mechanism: Pharmacodynamic (additive), not pharmacokinetic. Both agents independently prolong the QT interval; neither is a prodrug in a way that alters this.
- Direction: Additive QT effect (increased risk).
- Onset: Unspecified.
- Evidence: Theoretical.
- Severity: Contraindicated.
Management: Combination is contraindicated. Avoid coadministration; select a non-QT-prolonging antihistamine alternative. If concurrent QT-affecting therapy is unavoidable, ECG and electrolyte (K+, Mg2+) monitoring would be warranted, but avoidance is preferred here.
What happens
An increased risk of QT interval prolongation
Interaction Deep Dive
Taking terfenadine together with agents known to prolong the QT interval is contraindicated, because such combined administration can heighten the likelihood of QT prolongation and dangerous ventricular arrhythmias1.
Why it happens (mechanism)
Additive QT interval prolongation
How to manage this interaction
Because both medicines can affect your heart rhythm, this combination is one that care teams generally avoid altogether. Here is what usually happens:
- Your prescriber will likely choose a different allergy medicine in place of terfenadine, since safer options are available.
- Your team may check your heart tracing (ECG) and blood minerals like potassium and magnesium if there is any overlap.
What you should do: Keep taking your medicines as prescribed for now, and do not stop anything on your own. Contact your pharmacist or doctor promptly so they can adjust your therapy, and mention any dizziness, fainting, or palpitations.
Management is individual — confirm any change with your pharmacist or prescriber.
Common questions
Can I take Relugolix and Terfenadine together?
Relugolix and terfenadine can both prolong the QT interval, and combining them is contraindicated because the heart-rhythm risk adds up; ask your doctor or pharmacist to switch you to a safer allergy medicine. Always confirm with your pharmacist or prescriber before making any change.
How serious is the Relugolix and Terfenadine 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 Relugolix and Terfenadine interaction managed?
Because both medicines can affect your heart rhythm, this combination is one that care teams generally avoid altogether. Here is what usually happens: Your prescriber will likely choose a different allergy medicine in place of terfenadine, since safer options are available. Your team may check your heart tracing (ECG) and blood minerals like potassium and magnesium if there is any overlap. What yo… 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.
Questions for your pharmacist
- Does my dose of Relugolix or Terfenadine 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 Relugolix
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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