Relugolix and Eribulin: 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
Eribulin
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 your medicines can affect your heart's electrical timing, something doctors call the QT interval. Relugolix (Orgovyx) lowers testosterone, which can slightly stretch out that timing, and eribulin (Halaven) can do the same thing. When you take them together, those small effects can add up and, rarely, lead to an abnormal heart rhythm.
The good news is that this concern is mostly theoretical, and your care team can manage it well. They may check your heart rhythm with an ECG and keep an eye on your blood minerals like potassium and magnesium. Please keep taking both as prescribed and talk with your pharmacist or doctor about any dizziness, fainting, or palpitations.
Effect: Additive QT prolongation risk with coadministration of relugolix and eribulin.
Mechanism: Pharmacodynamic (additive), not PK. Androgen deprivation from relugolix can prolong QTc; eribulin independently carries QT-prolonging potential. Neither is a prodrug here; direction is additive PD effect.
Evidence: Theoretical. Onset: Unspecified. Severity: Major.
Management:
- Weigh benefits of ADT against risk in congenital long QT, CHF, or recurrent electrolyte disturbances.
- Avoid concomitant use when feasible.
- If combined, correct and avoid hypokalemia/hypomagnesemia.
- Consider periodic ECG and electrolyte monitoring.
What happens
Increased risk of QT interval prolongation
Interaction Deep Dive
When relugolix is given together with drugs that prolong the QT interval, the effects on the QT interval are additive. The androgen deprivation produced by GnRH agonists and antagonists can itself lengthen the QT interval. In patients who have congenital long QT syndrome, congestive heart failure, or recurrent electrolyte disturbances, as well as in those receiving medications recognized to prolong the QT interval, weigh whether the advantages of androgen deprivation therapy such as relugolix are greater than the possible hazards 1. Where feasible, do not use relugolix alongside QT prolonging agents. Should combined use be necessary, refrain from using drugs that produce electrolyte disturbances (that is, hypokalemia or hypomagnesemia) 2, correct any electrolyte abnormalities, and think about periodic monitoring of ECGs and electrolytes 1.
Why it happens (mechanism)
Additive QT interval prolongation
How to manage this interaction
Your care team can manage this combination safely with some monitoring.
- Keep taking both medicines exactly as prescribed unless your doctor tells you otherwise.
- Your team may order periodic ECGs to check your heart rhythm and blood tests for potassium and magnesium.
- They will work to correct any low electrolytes and avoid other drugs that lower them.
- In some cases they may choose an alternative or reassess whether the therapy's benefits outweigh the risks.
Tell your pharmacist or prescriber right away if you feel fainting, palpitations, or a fast or irregular heartbeat.
Management is individual — confirm any change with your pharmacist or prescriber.
Literature reports
1 report — tap to read
a) In an analysis of male patients on androgen deprivation therapy (ADT) using individual case safety reports from VigiBase, the international pharmacovigilance database, investigators identified 184 cases of acquired long-QT syndrome (aLQTS) and/or torsades de pointes (TdP; 11% of cases fatal), along with 99 cases of sudden death linked to ADT. The majority of aLQTS/TdP cases (62%) and sudden death cases (88%) tied to ADT arose without concurrent use of other agents known to elevate TdP risk; nonetheless, use of 1 drug and of 2 or more drugs with conditional, possible, or known TdP risk was reported in a portion of aLQTS/TdP (23% or 43%) and sudden death (18% and 22%) events. The agents regarded as ADTs included abiraterone, gonadotropin-releasing hormone agonists and antagonists, nonsteroidal androgen receptor inhibitors indicated for prostate cancer, and 5-alpha-reductase inhibitors indicated for androgenic alopecia and prostatism. Among the 10 ADTs assessed, 7 showed a disproportional association (reporting odds ratio, 1.4 to 4.7) with aLQTS, TdP, or sudden death, namely leuprorelin, goserelin, triptorelin, degarelix, bicalutamide, finasteride, and dutasteride. The median patient age was approximately 76 years, and the median time to onset was 170 days (range, 7 to 4884 days) for aLQTS/TdP events and 92 days (range, 0.25 to 4984 days) for sudden death events. Patients were mainly receiving ADT for prostate cancer, with some treated for prostatism and androgenic alopecia. Most patients were on ADT monotherapy (83%); 17% were on ADT combination therapy 3.
Common questions
Can I take Relugolix and Eribulin together?
Relugolix and eribulin can both prolong the QT interval, and using them together may add up, so your care team may monitor your ECG and electrolytes. Keep taking both as prescribed and report any fainting or irregular heartbeat. Always confirm with your pharmacist or prescriber before making any change.
How serious is the Relugolix and Eribulin 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 Relugolix and Eribulin interaction managed?
Your care team can manage this combination safely with some monitoring. Keep taking both medicines exactly as prescribed unless your doctor tells you otherwise. Your team may order periodic ECGs to check your heart rhythm and blood tests for potassium and magnesium. They will work to correct any low electrolytes and avoid other drugs that lower them. In some cases they may choose an alternative or… 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 Eribulin 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 (3)
- Product Information: ORGOVYX oral tablets, relugolix oral tablets. Sumitomo Pharma America, Inc (per FDA), Marlborough, MA, 2025. DailyMed
- Lyon AR, Lopez-Fernandez T, Couch LS, et al: 2022 ESC guidelines on cardio-oncology developed in collaboration with the European Hematology Association (EHA), the European Society for Therapeutic Radiology and Oncology (ESTRO) and the International Cardio-Oncology Society (IC-OS). Eur Heart J 2022; 43(41):4229-4361.
- Salem JE, Yang T, Moslehi JJ, et al: Androgenic effects on ventricular repolarization: a translational study from the international pharmacovigilance database to iPSC-cardiomyocytes. Circulation 2019; 140(13):1070-1080. PubMed
Keep reading about Relugolix
Keep reading about Eribulin
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