Simvastatin and Ritlecitinib: 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
Ritlecitinib
Simvastatin
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.
You've been prescribed Litfulo (ritlecitinib) for hair loss and simvastatin (like Zocor) for cholesterol. Here's the simple version: ritlecitinib slows down an enzyme in your body called CYP3A that helps break down simvastatin. When that enzyme is slowed, more simvastatin can build up in your blood than usual.
Higher statin levels can raise the chance of side effects, especially muscle aches, muscle weakness, or (rarely) muscle damage. The good news is this is very manageable. Your care team can adjust your simvastatin dose or keep a closer eye on you. Please don't stop either medicine on your own. Just let your doctor or pharmacist know you're taking both, and tell them right away if you get unusual muscle pain.
Mechanism: Ritlecitinib is a CYP3A inhibitor; simvastatin is a sensitive CYP3A4 substrate. Inhibition reduces simvastatin clearance, increasing its systemic exposure (AUC/Cmax) and the risk of dose-dependent toxicity, notably myopathy and rhabdomyolysis.
Magnitude: With midazolam (a probe CYP3A substrate), ritlecitinib 200 mg daily x11 days raised AUC 2.69-fold and Cmax 1.81-fold; a comparable effect on simvastatin is expected.
Evidence: Probable. Onset: unspecified. Severity: major.
- Consider simvastatin dose reduction, individualized by the care team.
- Monitor for muscle pain/weakness; consider CK and hepatic monitoring if symptomatic.
- Counsel patient to report myalgia promptly.
What happens
Increased CYP3A substrate exposure and an increased risk of CYP3A substrate-related adverse reactions
Interaction Deep Dive
When sensitive CYP3A substrates are taken together with ritlecitinib, the exposure to those substrates rises, potentially heightening the likelihood of adverse reactions linked to them. For substrates where minor shifts in concentration could trigger serious adverse reactions during ritlecitinib co-administration, consider extra monitoring along with dose modifications. Administering ritlecitinib at 200 mg once daily over 11 days alongside midazolam (a sensitive CYP3A substrate) raised midazolam's AUC by 2.69-fold and its Cmax by 1.81-fold1.
Why it happens (mechanism)
Inhibition of CYP3A-substrate metabolism by ritlecitinib
How to manage this interaction
This combination can be managed well by your care team. Because ritlecitinib can raise simvastatin levels, your team may take a few practical steps:
- Dose adjustment: your simvastatin dose may need to be adjusted and individualized by your prescriber.
- Closer monitoring: your team may watch you more closely for statin side effects.
What you should do:
- Keep taking both medicines exactly as prescribed unless your doctor tells you otherwise.
- Tell your pharmacist or prescriber that you take both drugs.
- Report any new or unusual muscle pain, tenderness, or weakness, or dark urine, right away.
Management is individual — confirm any change with your pharmacist or prescriber.
Literature reports
1 report — tap to read
a) Administering ritlecitinib 200 mg once daily for 11 days together with midazolam (a sensitive CYP3A substrate) raised the AUC(inf) and Cmax of midazolam by 2.69-fold and 1.81-fold, respectively 1.
Common questions
Can I take Simvastatin and Ritlecitinib together?
Ritlecitinib can raise simvastatin levels and increase the risk of muscle-related side effects, so keep taking both as prescribed but let your care team know so they can adjust the dose and watch for muscle pain. Always confirm with your pharmacist or prescriber before making any change.
How serious is the Simvastatin and Ritlecitinib 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 Simvastatin and Ritlecitinib interaction managed?
This combination can be managed well by your care team. Because ritlecitinib can raise simvastatin levels, your team may take a few practical steps: Dose adjustment: your simvastatin dose may need to be adjusted and individualized by your prescriber. Closer monitoring: your team may watch you more closely for statin side effects. What you should do: Keep taking both medicines exactly as prescribed… Management is individual — always follow your own care team's guidance.
How strong is the evidence for this interaction?
The evidence is graded "probable". Good supporting evidence, though not definitively proven.
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 Ritlecitinib 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: LITFULO(TM) oral capsules, ritlecitinib oral capsules. Pfizer Labs (per FDA), New York, NY, 2023. DailyMed
Keep reading about Ritlecitinib
Keep reading about Simvastatin
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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