Abemaciclib and St John's Wort: 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
St John's Wort
No brand names on recordAbemaciclib
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.
St John's Wort can weaken your cancer medicine abemaciclib (Verzenio). St John's Wort is an herbal supplement that speeds up the liver enzyme (called CYP3A4) that breaks down abemaciclib. When your body clears the drug faster, less of it stays in your blood, so it may not fight your cancer as well as it should.
This concern comes from how these drugs behave in the body rather than from direct studies, but because abemaciclib is treating something serious, it matters. Please don't stop or change anything on your own. Let your oncologist and pharmacist know about any supplements you take, and they can guide you to a safer option.
Effect: St John's Wort, a strong CYP3A4 inducer, may reduce abemaciclib plasma concentrations and those of its active metabolites, potentially lowering antineoplastic efficacy.
- Mechanism: Induction of CYP3A4-mediated abemaciclib metabolism.
- Direction: Reduced abemaciclib exposure (neither agent is activated by this pathway; abemaciclib's active metabolites also decrease).
- Magnitude: Rifampin (strong inducer) decreased abemaciclib AUC by ~67%; St John's Wort effect is extrapolated.
- Evidence: Theoretical; onset unspecified (enzyme induction typically develops over days).
- Management: Avoid coadministration; consider alternative agents. Consult oncology/pharmacy.
What happens
Decreased abemaciclib plasma concentration
Interaction Deep Dive
Taking abemaciclib together with a potent CYP3A4 inducer can lower the plasma concentrations of both abemaciclib and its active metabolite, potentially reducing its effectiveness. Study data showed that giving it alongside rifampin (a strong CYP3A4 inducer) reduced abemaciclib exposure by 67%. This combination should not be used, and alternative agents should be considered1.
Why it happens (mechanism)
Induction of CYP3A4-mediated abemaciclib metabolism
How to manage this interaction
The main step here is avoiding the combination. Because St John's Wort can significantly lower abemaciclib levels, your care team will generally steer you away from using them together.
- Keep taking your abemaciclib as prescribed and do not stop your cancer treatment on your own.
- Tell your oncologist and pharmacist about St John's Wort and any other herbal or over-the-counter supplements.
- Your team may recommend an alternative to St John's Wort so your cancer medicine keeps working as intended.
This is very manageable once your care team knows what you are taking.
Management is individual — confirm any change with your pharmacist or prescriber.
Literature reports
1 report — tap to read
a) In drug interaction investigations conducted in healthy volunteers, giving a single 200 mg dose of abemaciclib together with rifampin 600 mg daily (a potent CYP3A inducer) reduced the AUC(0 to infinity) of abemaciclib together with its active metabolites (M2, M18, and M20) by 67% 1.
Common questions
Can I take Abemaciclib and St John's Wort together?
St John's Wort can lower abemaciclib (Verzenio) levels and may make it less effective, so this combination should be avoided. Tell your oncologist and pharmacist about any supplements and let them suggest a safer choice. Always confirm with your pharmacist or prescriber before making any change.
How serious is the Abemaciclib and St John's Wort 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 Abemaciclib and St John's Wort interaction managed?
The main step here is avoiding the combination. Because St John's Wort can significantly lower abemaciclib levels, your care team will generally steer you away from using them together. Keep taking your abemaciclib as prescribed and do not stop your cancer treatment on your own. Tell your oncologist and pharmacist about St John's Wort and any other herbal or over-the-counter supplements. Your team… 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 Abemaciclib or St John's Wort 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 (1)
- Product Information: VERZENIO(TM) oral tablets, abemaciclib oral tablets. Lilly USA LLC (per FDA), Indianapolis, IN, 2017. DailyMed
Keep reading about St John's Wort
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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