Relugolix and Ondansetron: 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
Ondansetron
No brand names on recordRelugolix
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 the timing of your heartbeat. Ondansetron (an anti-nausea medicine) and relugolix (Orgovyx, used to lower testosterone in prostate cancer) can each slightly stretch out a part of the heart's electrical cycle called the QT interval. When taken together, that effect can add up, which in rare cases can lead to an irregular heartbeat.
The good news is this is a possible risk based on how these drugs work, not something everyone will experience. Your care team can manage it by keeping your minerals (like potassium and magnesium) in balance and checking your heart tracing when needed. Please don't stop either medicine on your own, just talk with your pharmacist or doctor.
Effect: Additive QT interval prolongation with combined use of ondansetron and relugolix.
Mechanism: Pharmacodynamic (additive), not pharmacokinetic. Ondansetron prolongs QT in a dose-dependent manner; androgen deprivation from relugolix (a GnRH antagonist) can also prolong QT. Neither is a prodrug; direction is additive PD risk.
Evidence: Theoretical. Onset: unspecified. Severity: major.
- Avoid concomitant use when possible.
- Higher risk with congenital long QT, CHF, or electrolyte disturbances.
- If combined, correct/avoid hypokalemia and hypomagnesemia and consider periodic ECG and electrolyte monitoring.
What happens
Increased risk of QT interval prolongation
Interaction Deep Dive
When relugolix is given together with medications that prolong the QT interval, the effects on QT interval are additive. The androgen deprivation produced by GnRH agonists and antagonists can itself prolong the QT interval. In patients with congenital long QT syndrome, congestive heart failure, or recurrent electrolyte disturbances, as well as those receiving drugs recognized to prolong the QT interval, weigh whether the advantages of androgen deprivation therapy such as relugolix are greater than the possible risks 1. Where feasible, do not use relugolix alongside QT prolonging agents. Should coadministration be necessary, refrain from using drugs that produce electrolyte disturbances (ie, hypokalemia or hypomagnesemia) 2, correct any electrolyte disturbances, and consider periodic monitoring of ECGs and electrolytes 1.
Why it happens (mechanism)
Additive QT interval prolongation
How to manage this interaction
Both drugs can add to each other's effect on the heart's QT interval, so your care team will weigh the benefits against the risks and prefer to avoid using them together when possible.
If you do need both:
- Your team may keep your potassium and magnesium levels in a healthy range and correct any imbalances.
- They may check periodic ECGs (heart tracings) and blood electrolytes.
- Extra caution applies if you have a heart rhythm condition, heart failure, or frequent electrolyte problems.
What you should do: Keep taking both exactly as prescribed and ask your pharmacist or doctor before making changes. Report fainting, dizziness, or palpitations right away.
Management is individual — confirm any change with your pharmacist or prescriber.
Literature reports
1 report — tap to read
a) A study assessed male patients on androgen deprivation therapy (ADT) using individual case safety reports from VigiBase, the international pharmacovigilance database, and found 184 cases of acquired long-QT syndrome (aLQTS) and/or torsades de pointes (TdP; 11% fatal cases), 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 exposure to other agents known to elevate TdP risk; nevertheless, exposure to 1 drug and to 2 or more drugs carrying conditional, possible, or known TdP risk was documented in some 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 patients had a median age of roughly 76 years, and the median time to onset of aLQTS/TdP events was 170 days (range, 7 to 4884 days) while for sudden death events it was 92 days (range, 0.25 to 4984 days). Patients received ADT chiefly for prostate cancer treatment, with some treated for prostatism and androgenic alopecia. The majority of patients were on ADT monotherapy (83%); 17% received ADT combination therapy 3.
Common questions
Can I take Relugolix and Ondansetron together?
Ondansetron and relugolix can each prolong the QT interval, and together the effect may add up, so your care team may avoid the combination, keep your electrolytes balanced, and monitor your heart. Do not stop either drug on your own. Always confirm with your pharmacist or prescriber before making any change.
How serious is the Relugolix and Ondansetron 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 Ondansetron interaction managed?
Both drugs can add to each other's effect on the heart's QT interval, so your care team will weigh the benefits against the risks and prefer to avoid using them together when possible. If you do need both: Your team may keep your potassium and magnesium levels in a healthy range and correct any imbalances. They may check periodic ECGs (heart tracings) and blood electrolytes. Extra caution applies… 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 Relugolix or Ondansetron 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 Ondansetron
Keep reading about Relugolix
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