Abemaciclib and Tizanidine: 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
Tizanidine
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.
Here's what's going on. Tizanidine is a muscle relaxer, and your body clears it out using a liver enzyme called CYP1A2. Abemaciclib (Verzenio) can slow that enzyme down. When that happens, tizanidine can build up in your system more than expected.
That extra buildup can make tizanidine's usual effects stronger, so you might feel very drowsy, dizzy, or lightheaded, or notice a slower heartbeat or a drop in blood pressure. The good news is this is manageable. Please don't stop or change either medicine on your own. Talk with your pharmacist or doctor, since they can adjust your dose and watch you more closely.
Effect: Abemaciclib may inhibit CYP1A2-mediated metabolism of tizanidine, increasing tizanidine exposure (AUC/Cmax) and the risk of hypotension, bradycardia, and sedation. Neither agent is a prodrug here, so this is a straightforward exposure increase in the active drug.
- Direction: increased tizanidine effect and toxicity.
- Severity/Evidence: major, but theoretical (no clinical exposure data quantified).
- Onset: unspecified.
Management: Avoid concomitant use where possible. If clinically necessary, reduce the tizanidine dose or discontinue it, and monitor blood pressure, heart rate, and CNS/sedation status closely.
What happens
Increased tiZANidine exposure and an increased risk of tiZANidine-related hypotension, bradycardia or increased drowsiness
Interaction Deep Dive
The combined use of tiZANidine with weak or moderate CYP1A2 inhibitors should be avoided, since it can raise tiZANidine exposure and heighten the likelihood of tiZANidine-associated bradycardia, hypotension, or greater drowsiness. When such concurrent use is clinically required, either lower the tiZANidine dose or stop tiZANidine therapy1.
Why it happens (mechanism)
Inhibition of CYP1A2-mediated metabolism of tiZANidine
How to manage this interaction
What your care team may do:
- Where possible, avoid using these two together, or consider an alternative muscle relaxer.
- If both are needed, your tizanidine dose may be reduced and individualized, or tizanidine may be stopped.
- Your team may monitor you more closely for low blood pressure, slow heart rate, and excess drowsiness.
What you should do: Keep taking both exactly as prescribed for now, and don't change anything on your own. Tell your pharmacist or prescriber you take both, and report new dizziness, fainting, unusual sleepiness, or a slow heartbeat.
Management is individual — confirm any change with your pharmacist or prescriber.
Common questions
Can I take Abemaciclib and Tizanidine together?
Abemaciclib can raise tizanidine levels and increase its side effects (drowsiness, low blood pressure, slow heart rate), so ask your pharmacist or doctor before combining them; they may lower the tizanidine dose or monitor you more closely. Always confirm with your pharmacist or prescriber before making any change.
How serious is the Abemaciclib and Tizanidine 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 Tizanidine interaction managed?
What your care team may do: Where possible, avoid using these two together, or consider an alternative muscle relaxer. If both are needed, your tizanidine dose may be reduced and individualized, or tizanidine may be stopped. Your team may monitor you more closely for low blood pressure, slow heart rate, and excess drowsiness. What you should do: Keep taking both exactly as prescribed for now, and… 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 Abemaciclib or Tizanidine 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: ZANAFLEX(R) oral capsules, oral tablets, tizanidine HCl oral capsules, oral tablets. Legacy Pharma Inc. (per FDA), Georgetown, Grand Cayman, 2024. DailyMed
Keep reading about Tizanidine
Keep reading about Abemaciclib
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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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