Phenytoin and Cariprazine: Interaction Details
AI-assisted, pharmacist-reviewed · AI content regenerated Jul 16, 2026 · Source data updated Jul 16, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature
Phenytoin
Cariprazine
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.
Phenytoin (Dilantin) can speed up how your body handles cariprazine (Vraylar). Phenytoin turns up an enzyme called CYP3A4, and that enzyme both builds and breaks down the active pieces of cariprazine. Because of that, phenytoin can change your cariprazine levels. The tricky part is that the exact result has not been studied, so we cannot say for sure whether your Vraylar becomes weaker or works differently.
The good news is your care team can handle this. Please do not stop or change either medicine on your own. Just let your doctor or pharmacist know you take both, and they can watch how you are doing and adjust things if needed.
Direction: Phenytoin is a strong CYP3A4 inducer; cariprazine is a CYP3A4 substrate. CYP3A4 mediates both formation and elimination of cariprazine's active metabolites (DDCAR, DCAR), so the net effect on total active-moiety exposure is unpredictable rather than simply reduced.
- Effect: Altered cariprazine exposure; net direction unclear.
- Evidence: Theoretical; not formally evaluated.
- Onset: Unspecified (induction typically develops over days to weeks).
- Severity: Major; coadministration not recommended.
Management: Avoid the combination where possible. If used together, individualize dosing and monitor closely for loss of efficacy or altered response.
What happens
Effects on the cariprazine exposure has not been evaluated and the net effect is unclear
Interaction Deep Dive
It is not advised to give cariprazine (which is metabolized by CYP3A4) together with a CYP3A4 inducer. The generation as well as the clearance of cariprazine's active metabolites depend on CYP3A4. No assessment has been made of how CYP3A4 inducers alter cariprazine exposure, so the overall consequence remains uncertain1.
Why it happens (mechanism)
Induction of CYP3A4-mediated metabolism of cariprazine
How to manage this interaction
What your care team may do:
- Consider whether the two drugs should be used together at all, since this combination is generally not recommended.
- Watch you more closely for changes in how well the cariprazine is controlling your symptoms.
- Adjust and individualize your dose if your response changes.
- Consider an alternative if needed.
What you should do: Keep taking both exactly as prescribed unless told otherwise. Tell your pharmacist and prescriber that you take both, and report any return or worsening of symptoms so they can respond.
Management is individual — confirm any change with your pharmacist or prescriber.
Common questions
Can I take Phenytoin and Cariprazine together?
Phenytoin can unpredictably change cariprazine levels by speeding up the enzyme that handles it, so this combination is generally avoided. Keep taking both as prescribed and let your doctor or pharmacist know you use both so they can monitor and adjust. Always confirm with your pharmacist or prescriber before making any change.
How serious is the Phenytoin and Cariprazine 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 Phenytoin and Cariprazine interaction managed?
What your care team may do: Consider whether the two drugs should be used together at all, since this combination is generally not recommended. Watch you more closely for changes in how well the cariprazine is controlling your symptoms. Adjust and individualize your dose if your response changes. Consider an alternative if needed. What you should do: Keep taking both exactly as prescribed unless t… 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 Phenytoin or Cariprazine 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: VRAYLAR(R) oral capsules, cariprazine oral capsules. AbbVie Inc. (per FDA), North Chicago, IL, 2024. DailyMed
Keep reading about Phenytoin
Keep reading about Cariprazine
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