Relugolix and Vandetanib: 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
Vandetanib
Relugolix
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.
Taking vandetanib (Caprelsa) together with relugolix (Orgovyx) can raise the amount of relugolix in your body. That is because vandetanib can block a transporter that normally helps push relugolix out, so more of it hangs around and side effects become more likely.
There is also a second concern: both of these drugs can affect your heart's rhythm by lengthening what is called the QT interval. Together that effect can add up. This warning is based on how the drugs work rather than large studies, but it is taken seriously. The good news is your care team can manage this by adjusting timing, checking your heart tracing and blood minerals, and watching you a bit more closely.
Effect: Vandetanib may increase relugolix exposure and add to QT prolongation. Neither is a prodrug; relugolix is a P-gp substrate and vandetanib inhibits P-gp, so relugolix efflux is reduced and systemic exposure rises. Both agents independently prolong QT, giving additive risk.
- Direction: increased relugolix exposure and effect
- Evidence: theoretical; magnitude not quantified
- Onset: unspecified
Management: Avoid combination if possible. If unavoidable, give relugolix first and separate by >=6 hours. Correct electrolytes; perform periodic ECG and electrolyte monitoring. Relugolix may be interrupted up to 2 weeks for a short P-gp inhibitor course; if held >7 days, restart with a 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, because doing so can raise relugolix exposure and thereby heighten the likelihood of adverse reactions. When coadministration cannot be avoided, give the relugolix-containing product first, keep the doses at least 6 hours apart, and increase how often patients are monitored for adverse reactions12. Relugolix therapy may be paused for as long as 2 weeks to allow a brief course of a P-gp inhibitor. Once the P-gp inhibitor is stopped, relugolix can be resumed. When relugolix has been interrupted for more than 7 days, restart it with a 360 mg loading dose on day one, then continue at 120 mg once daily1. Giving relugolix alongside drugs that prolong the QT interval may produce additive QT interval effects. In patients with congenital long QT syndrome, congestive heart failure, or frequent electrolyte abnormalities, as well as those on medications recognized to prolong the QT interval, weigh whether the benefits of androgen deprivation therapy such as relugolix are greater than the possible risks. Correct any electrolyte abnormalities and consider monitoring ECGs and electrolytes periodically1.
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 exactly as prescribed unless your care team tells you otherwise. This combination is usually avoided when possible, but your team may decide the cancer treatment benefit is worth it and manage the risk closely.
- Timing: If used together, your team may have you take relugolix first and separate the doses by at least 6 hours.
- Monitoring: Expect possible ECG (heart tracing) checks and blood tests for electrolytes, which they will correct if needed.
- Dosing: Your relugolix schedule may be adjusted and individualized by your team, especially if it is paused.
Tell your pharmacist or doctor if you feel dizzy, faint, or have 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 and 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 Vandetanib together?
Combining vandetanib and relugolix can raise relugolix levels and add to heart-rhythm (QT) risk, so it is usually avoided; if used together, your care team will separate dosing and monitor your ECG and electrolytes. Always confirm with your pharmacist or prescriber before making any change.
How serious is the Relugolix and Vandetanib 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 Vandetanib interaction managed?
Keep taking both medicines exactly as prescribed unless your care team tells you otherwise. This combination is usually avoided when possible, but your team may decide the cancer treatment benefit is worth it and manage the risk closely. Timing: If used together, your team may have you take relugolix first and separate the doses by at least 6 hours. Monitoring: Expect possible ECG (heart tracing)… 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 Vandetanib 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 Vandetanib
Keep reading about Relugolix
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