Relugolix and Mizolastine: 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
Mizolastine
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 your medicines can affect the timing of your heartbeat. Relugolix (Orgovyx) lowers testosterone, which by itself can slightly stretch out part of the heart's electrical cycle, called the QT interval. Mizolastine, an antihistamine, can do the same thing. When you take them together, those effects can add up and, in rare cases, lead to an abnormal heart rhythm.
This is based mostly on how these drugs are expected to behave, not on lots of real-world reports, so please don't panic. The good news is your care team can manage this by checking your heart rhythm and your blood minerals (like potassium and magnesium). Talk with your pharmacist or doctor before changing anything.
Effect: Additive QT interval prolongation (PD interaction), not a metabolic interaction. Neither agent depends on the other for activation.
Mechanism: Relugolix-induced androgen deprivation can prolong QT; mizolastine has intrinsic QT-prolonging potential. Effects are additive.
Evidence: Theoretical; severity rated major. Onset unspecified.
- Avoid concomitant use where possible.
- Weigh benefits of ADT against risk in congenital long QT, CHF, or recurrent electrolyte disturbances.
- If coadministered: avoid agents causing hypokalemia/hypomagnesemia, correct electrolyte abnormalities, 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 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 drugs recognized to prolong the QT interval, weigh whether the advantages of androgen deprivation therapy such as relugolix outweigh the possible risks1. Where feasible, do not combine relugolix with QT prolonging agents. Should coadministration be necessary, steer clear of drugs that produce electrolyte abnormalities (namely, hypokalemia or hypomagnesemia)2, correct any electrolyte abnormalities, and consider periodic monitoring of ECGs and electrolytes1.
Why it happens (mechanism)
Additive QT interval prolongation
How to manage this interaction
Keep taking both medicines as prescribed unless your prescriber tells you otherwise. This combination is usually avoided when possible, so your care team will decide whether the benefit of relugolix outweighs the heart-rhythm risk for you.
If you do take them together, your team may:
- Check periodic ECGs to watch your heart rhythm.
- Monitor and correct blood minerals like potassium and magnesium.
- Steer clear of other drugs that lower those minerals.
Tell your pharmacist or doctor if you have a history of long QT, heart failure, or fainting spells, and report new dizziness or palpitations.
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 undergoing 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 in the absence of other agents recognized to raise TdP risk; nevertheless, use of 1 drug and 2 or more drugs carrying conditional, possible, or known TdP risk was documented in a portion of aLQTS/TdP events (23% or 43%) and sudden death events (18% and 22%). The agents classified as ADTs comprised 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 demonstrated 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 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 taking ADT chiefly for prostate cancer, with some treated for prostatism and androgenic alopecia. The majority of patients received ADT as monotherapy (83%), while 17% were on ADT combination therapy 3.
Common questions
Can I take Relugolix and Mizolastine together?
Combining relugolix and mizolastine can add up to prolong the QT interval, so this pairing is best avoided; if used together, your care team should monitor your ECG and keep your potassium and magnesium in a healthy range. Always confirm with your pharmacist or prescriber before making any change.
How serious is the Relugolix and Mizolastine 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 Mizolastine interaction managed?
Keep taking both medicines as prescribed unless your prescriber tells you otherwise. This combination is usually avoided when possible, so your care team will decide whether the benefit of relugolix outweighs the heart-rhythm risk for you. If you do take them together, your team may: Check periodic ECGs to watch your heart rhythm. Monitor and correct blood minerals like potassium and magnesium. St… 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 Mizolastine 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 Mizolastine
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