Relugolix and Quinidine: 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
Quinidine
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.
You've been prescribed relugolix (Orgovyx), a prostate cancer medicine, along with quinidine, a heart rhythm drug. There are two things worth knowing here. First, quinidine can block a 'pump' in your gut that normally limits how much relugolix gets into your body, so relugolix levels can rise and cause more side effects. Second, both drugs can affect your heart's electrical timing (called the QT interval), and together that effect can add up.
This is based mostly on how the drugs are expected to behave, not on lots of real-world reports. The good news is your care team can manage this easily by spacing the doses, checking your heart tracing (ECG) and blood salts, and watching you a little more closely. Please don't change anything on your own, just talk with your doctor or pharmacist.
Effect: Increased relugolix exposure plus additive QT prolongation.
Mechanism: Quinidine inhibits P-glycoprotein (P-gp), reducing efflux of relugolix (a P-gp substrate), raising its exposure. Both agents independently prolong the QT interval, giving additive PD risk. Neither is a prodrug here; effects are increased, not reduced.
Evidence: Theoretical; severity major; onset unspecified.
- Avoid concomitant use where possible.
- If unavoidable: give relugolix first, separate by at least 6 hours, monitor for adverse reactions more frequently.
- Correct electrolytes; consider periodic ECG and electrolyte monitoring.
- Weigh ADT benefit vs risk in congenital long QT, CHF, or frequent electrolyte disturbance.
- Relugolix may be interrupted up to 2 weeks for a short P-gp inhibitor course; if held over 7 days, restart with 360 mg loading dose then 120 mg daily.
What happens
Increased relugolix exposure and an increased risk of QT interval prolongation
Interaction Deep Dive
Do not use relugolix (a P-gp substrate) together with P-gp inhibitors, since this combination can raise relugolix exposure and thereby heighten the likelihood of adverse reactions. When coadministration cannot be avoided, take the relugolix-containing product first, allow a gap of no less than 6 hours between doses, and increase the frequency of monitoring for adverse reactions12. Relugolix therapy may be paused for as long as 2 weeks to accommodate a brief course of a P-gp inhibitor, with relugolix resumed once the P-gp inhibitor has been stopped. Should the relugolix interruption exceed 7 days, reinitiate it using a 360 mg loading dose on day one, followed by 120 mg once daily thereafter1. Giving relugolix alongside drugs that prolong the QT interval can produce additive effects on the QT interval. In patients who have congenital long QT syndrome, congestive heart failure, or frequent electrolyte disturbances, as well as in those receiving medications recognized to prolong the QT interval, weigh whether the benefits of androgen deprivation therapy such as relugolix outweigh the possible risks. Correct any electrolyte abnormalities and consider periodic ECG and electrolyte monitoring1.
Why it happens (mechanism)
Inhibition of P-gp-mediated efflux transport of relugolix; additive QT interval prolongation
How to manage this interaction
Keep taking both medicines as prescribed unless your care team tells you otherwise. This combination is often avoided, but when both are needed your team has clear ways to manage it.
- Your team may space the doses, giving relugolix first and separating by at least 6 hours.
- They may monitor you more closely, including periodic ECGs and blood electrolyte (potassium, magnesium) checks, and correct any imbalances.
- In some cases relugolix can be briefly paused during a short course of quinidine; any restart dosing will be individualized by your prescriber.
Tell your pharmacist or doctor about any dizziness, fainting, or heart palpitations, and mention any history of heart rhythm problems.
Management is individual — confirm any change with your pharmacist or prescriber.
Literature reports
1 report — tap to read
a) When relugolix (a P-gp substrate) was given together with erythromycin (a P-gp CYP3A inhibitor), the AUC and Cmax of relugolix rose by 3.5-fold and 2.9-fold, respectively 1.
Common questions
Can I take Relugolix and Quinidine together?
Combining relugolix and quinidine can raise relugolix levels and add to QT prolongation, so this pairing is usually avoided; if you must take both, your care team will space the doses and monitor your ECG and electrolytes. Do not change either medicine on your own. Always confirm with your pharmacist or prescriber before making any change.
How serious is the Relugolix and Quinidine 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 Quinidine interaction managed?
Keep taking both medicines as prescribed unless your care team tells you otherwise. This combination is often avoided, but when both are needed your team has clear ways to manage it. Your team may space the doses, giving relugolix first and separating by at least 6 hours. They may monitor you more closely, including periodic ECGs and blood electrolyte (potassium, magnesium) checks, and correct any… 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 Quinidine 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 (2)
- Product Information: ORGOVYX oral tablets, relugolix oral tablets. Sumitomo Pharma America, Inc (per FDA), Marlborough, MA, 2025. DailyMed
- Product Information: MYFEMBREE(R) oral tablets, relugolix, estradiol, norethindrone acetate oral tablets. Myovant Sciences Inc (per FDA), Brisbane, CA, 2021. DailyMed
Keep reading about Relugolix
Keep reading about Quinidine
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.
Check another combination
Our instant two-drug interaction checker is almost here.
Still have questions about this combination?
Every question gets a real answer from a licensed pharmacist — free, and usually within a day.
Ask the pharmacist