Simvastatin and Ensitrelvir: Interaction Details
AI-assisted, pharmacist-reviewed · AI content regenerated Jul 11, 2026 · Source data updated Jul 4, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature
Simvastatin
Ensitrelvir
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.
These two medicines should not be taken together. Ensitrelvir slows down a liver enzyme (called CYP3A) that normally breaks down your simvastatin. When that enzyme is blocked, simvastatin can build up to much higher levels than intended.
Too much simvastatin raises the risk of muscle problems, like aches, weakness, or in rare cases serious muscle breakdown that can affect the kidneys. The good news is this is very manageable. Your care team can plan the timing carefully, usually stopping simvastatin before starting ensitrelvir. Please don't change anything on your own, just check with your pharmacist or doctor so they can guide you safely.
Contraindicated combination. Ensitrelvir is a potent CYP3A inhibitor; simvastatin is a CYP3A (and BCRP) substrate. Inhibition reduces simvastatin metabolism, increasing systemic exposure (AUC/Cmax) and the risk of dose-dependent toxicity, notably myopathy and rhabdomyolysis.
- Direction: increased simvastatin effect/toxicity (neither drug is affected by prodrug activation issues here).
- Evidence: theoretical; magnitude not quantified.
- Management: discontinue simvastatin at least 12 hours before initiating ensitrelvir. Reinitiate the statin only after accounting for the duration of CYP3A inhibition and patient-specific factors. Monitor for muscle symptoms and CK if exposure is suspected.
What happens
Increased simvastatin exposure and an increased risk of simvastatin-related adverse events
Interaction Deep Dive
Because it can raise simvastatin (a BCRP/CYP3A substrate) exposure and thereby heighten adverse effects, taking ensitrelvir together with simvastatin is contraindicated. Simvastatin should be stopped no less than 12 hours before ensitrelvir is started. Ensitrelvir should be initiated only once the pertinent clinical and pharmacokinetic factors of the co-administered drug have been carefully weighed. Reintroduction of contraindicated CYP3A substrates should likewise be considered after evaluating how long CYP3A inhibition persists together with patient specific factors1.
Why it happens (mechanism)
Inhibition of CYP3A-mediated metabolism of simvastatin
How to manage this interaction
This pairing is contraindicated, but your care team can manage it safely with timing.
- Do not stop or change either medicine on your own. Instead, contact your prescriber or pharmacist so they can plan.
- Typically, simvastatin is stopped at least 12 hours before ensitrelvir is started.
- Restarting simvastatin is timed based on how long ensitrelvir keeps affecting the enzyme, and on your individual situation.
- Report any muscle pain, tenderness, weakness, or dark urine right away.
Your team may monitor you more closely and tailor timing to keep you safe.
Management is individual — confirm any change with your pharmacist or prescriber.
Literature reports
2 reports — tap to read
a) Giving ensitrelvir (a single 500 mg dose, which is not a recommended dosage of ensitrelvir) together with a single oral dose of a transporter cocktail that included 2.5 mg rosuvastatin (a BCRP substrate) produced a 1.97-fold rise in the Cmax and a 1.65-fold rise in the AUC(0 to inf) of rosuvastatin 1.
b) Giving midazolam (a CYP3A substrate) as a single 2 mg oral dose together with ensitrelvir at the clinical dose (375 mg on day 1 and 125 mg on days 2 to 5) on Day 5 produced an approximately 2.80-fold rise in Cmax and a 6.77-fold rise in AUC(0 to inf) of midazolam relative to midazolam given by itself. In addition, giving dexAMETHasone (a single 1 mg dose) together with ensitrelvir (750 mg on day 1 and 250 mg on days 2 to 5, twice the recommended dose) on day 5, and giving it alone on day 9 (5 days after the final ensitrelvir dose) and day 14 (10 days after the final ensitrelvir dose), produced an approximately 1.47-fold rise in Cmax and a 3.47-fold rise in AUC(0 to inf) of dexAMETHasone on day 5, a 1.24-fold rise in Cmax and a 2.38-fold rise in AUC(0 to inf) on day 9, and a 1.17-fold rise in Cmax and a 1.58-fold rise in AUC(0 to inf) on day 14, compared with dexAMETHasone given alone 1.
Common questions
Can I take Simvastatin and Ensitrelvir together?
Do not take simvastatin and ensitrelvir together, as simvastatin can build up and cause muscle harm. Contact your pharmacist or doctor to plan the timing safely; simvastatin is usually stopped at least 12 hours before ensitrelvir is started. Always confirm with your pharmacist or prescriber before making any change.
How serious is the Simvastatin and Ensitrelvir 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 Simvastatin and Ensitrelvir interaction managed?
This pairing is contraindicated, but your care team can manage it safely with timing. Do not stop or change either medicine on your own. Instead, contact your prescriber or pharmacist so they can plan. Typically, simvastatin is stopped at least 12 hours before ensitrelvir is started. Restarting simvastatin is timed based on how long ensitrelvir keeps affecting the enzyme, and on your individual si… 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.
From our Q&A
Real reader questions about these medications, each personally answered by our pharmacist:
Questions for your pharmacist
- Does my dose of Simvastatin or Ensitrelvir 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: XOCOVA® oral tablets, ensitrelvir oral tablets. Shionogi Inc. Florham Park, NJ, 2026. DailyMed
Keep reading about Simvastatin
Keep reading about Ensitrelvir
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