Mifepristone and Abemaciclib: Interaction Details
AI-assisted, pharmacist-reviewed · AI content regenerated Jul 11, 2026 · Source data updated Jul 10, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature
Mifepristone
Abemaciclib
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.
Mifepristone can make abemaciclib (Verzenio) build up in your body. Mifepristone strongly blocks a liver enzyme called CYP3A4, which is the same enzyme your body uses to break down and clear abemaciclib. When that clean-up slows down, more of the cancer medicine stays in your blood, which can raise the risk of side effects like low blood counts, diarrhea, and fatigue.
One more thing: mifepristone leaves the body very slowly, so this effect can last for a while even after it is stopped. The good news is your care team can manage this by adjusting doses, watching you closely, or choosing a different approach. Please don't change anything on your own, just check in with your doctor or pharmacist.
Mechanism: Mifepristone is a strong CYP3A4 inhibitor; abemaciclib is a CYP3A4 substrate. Inhibition reduces abemaciclib metabolism, increasing its exposure (AUC/Cmax) and toxicity risk (neutropenia, diarrhea, hepatotoxicity, ILD).
- Direction: Increased abemaciclib effect/exposure. Neither is a prodrug here.
- Severity: Contraindicated per labeling for CYP3A4 substrates with narrow therapeutic index.
- Evidence/onset: Theoretical; onset unspecified.
- Management: Avoid coadministration. If unavoidable, consider abemaciclib dose reduction and intensified monitoring (CBC, LFTs, GI toxicity). Given mifepristone's long terminal half-life, allow at least 2 weeks after stopping mifepristone before starting the substrate.
What happens
Increased CYP3A4 substrate with NTI exposure
Interaction Deep Dive
Giving miFEPRIStone (a strong CYP3A4 inhibitor) (Korlym®) together with CYP3A4 substrates that have a narrow therapeutic index (NTI) is contraindicated, since it can raise the exposure of these CYP3A4 substrates with NTI. Should they be used together, it may be necessary to stop or lower the dose of the CYP3A4 substrates with NTI 1. Caution is likewise warranted when miFEPRIStone (Mifeprex®) is given alongside CYP3A4 substrates with NTI. Because miFEPRIStone is cleared slowly from the body, this interaction can persist for an extended time following its administration 2. Given the long terminal half-life of miFEPRIStone once steady state is achieved, allow a minimum of 2 weeks to pass after discontinuing miFEPRIStone before starting CYP3A4 substrates with NTI 1.
Why it happens (mechanism)
Inhibition of CYP3A4-substrate metabolism by miFEPRIStone
How to manage this interaction
Your care team treats this combination as one to avoid when possible, because mifepristone can raise abemaciclib levels and side effects.
- Keep taking both exactly as prescribed until your doctor tells you otherwise, and do not stop or change doses on your own.
- If both must be used, the abemaciclib dose may need to be adjusted and individualized by your care team, and they may monitor you more closely (blood counts, liver tests, and for diarrhea).
- Because mifepristone clears very slowly, this effect can linger, so your team may wait a period of time (at least about 2 weeks) after stopping mifepristone before starting abemaciclib.
- Tell your pharmacist or prescriber about all your medicines and report new or worsening side effects promptly.
Management is individual — confirm any change with your pharmacist or prescriber.
Literature reports
1 report — tap to read
a) In a drug interaction study, giving miFEPRIStone 1200 mg once daily for 10 days together with a single 80 mg dose of simvastatin (a CYP3A4 substrate) produced increases in simvastatin AUC and Cmax of 10.40-fold and 7.02-fold, respectively. It also produced increases in simvastatin acid AUC and Cmax of 15.7-fold and 18.20, respectively 1.
Common questions
Can I take Mifepristone and Abemaciclib together?
Mifepristone strongly blocks the enzyme that clears abemaciclib, which can push abemaciclib levels and side effects higher, so this pairing is generally avoided. Do not change either drug yourself; talk with your doctor or pharmacist about safer options or closer monitoring. Always confirm with your pharmacist or prescriber before making any change.
How serious is the Mifepristone and Abemaciclib interaction?
It is rated contraindicated. These should generally not be used together.
How quickly could this interaction happen?
The documented onset is "unspecified". The timing of this interaction is not well characterized.
How is the Mifepristone and Abemaciclib interaction managed?
Your care team treats this combination as one to avoid when possible, because mifepristone can raise abemaciclib levels and side effects. Keep taking both exactly as prescribed until your doctor tells you otherwise, and do not stop or change doses on your own. If both must be used, the abemaciclib dose may need to be adjusted and individualized by your care team, and they may monitor you more clos… 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 Mifepristone or Abemaciclib 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)
Keep reading about Mifepristone
Keep reading about Abemaciclib
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.
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