Diltiazem 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
Diltiazem
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.
Diltiazem (a blood pressure and heart medicine) slows down a liver enzyme that normally breaks down cariprazine (Vraylar). When that enzyme is slowed, more cariprazine and its active byproduct build up in your body. That can mean stronger effects and a higher chance of side effects like restlessness, tremor, drowsiness, or trouble sitting still.
The good news is this is very manageable. Your care team knows about this combination and can simply use a lower cariprazine dose and keep a closer eye on how you feel. Please don't stop or change either medicine on your own. Just check in with your doctor or pharmacist so they can tailor your dose safely.
Mechanism: Diltiazem is a moderate CYP3A4 inhibitor; cariprazine is a CYP3A4 substrate. Inhibition reduces clearance, increasing exposure (AUC/Cmax) of cariprazine and its active metabolite didesmethylcariprazine (DDCAR), which has a long half-life. Direction is increased effect/toxicity risk. Evidence: probable; severity major.
Management (per labeling):
- Schizophrenia/bipolar mania, initiating cariprazine on inhibitor: 1.5 mg every other day, titrate cautiously.
- Bipolar depression/adjunctive MDD: 1.5 mg every other day.
- Stable on 1.5 or 3 mg daily, adding inhibitor: reduce to 1.5 mg every other day.
- Stable on 4.5 or 6 mg daily: reduce to 1.5 mg daily.
- On inhibitor discontinuation: cariprazine dose may need increasing per response.
Monitor for extrapyramidal symptoms, akathisia, sedation.
What happens
Increased cariprazine and its major active metabolite (didesmethylcariprazine (DDCAR)) exposure
Interaction Deep Dive
Taking cariprazine (a substrate of CYP3A4) together with a moderate CYP3A4 inhibitor can raise the levels of both cariprazine and its active metabolite, didesmethylcariprazine. If cariprazine is being started in a patient already receiving a moderate CYP3A4 inhibitor (in schizophrenia or bipolar mania), begin with 1.5 mg orally every other day, then, if warranted by clinical response and tolerability, titrate to 1.5 mg orally every other day. For a patient on a moderate CYP3A4 inhibitor being treated for bipolar depression or adjunctive treatment of MDD, use 1.5 mg orally every other day. When a moderate CYP3A4 inhibitor is added to a patient already on a stable cariprazine regimen, dosing should be modified as follows: for those currently taking 1.5 or 3 mg once daily, change cariprazine to 1.5 mg orally every other day when starting the inhibitor; for those currently taking cariprazine 4.5 or 6 mg once daily, change to 1.5 mg orally once daily when starting the inhibitor. Should the moderate CYP3A4 inhibitor later be stopped, the cariprazine dose may require an increase guided by clinical response and tolerability1.
Why it happens (mechanism)
Inhibition of CYP3A4-mediated metabolism of cariprazine
How to manage this interaction
Keep taking both medicines exactly as prescribed unless your care team tells you otherwise. Because diltiazem raises cariprazine levels, your team typically manages this by using a lower cariprazine dose and watching how you respond.
- They may start or adjust cariprazine at a reduced dose (for example, taking it every other day rather than daily) and individualize it to you.
- If diltiazem is later stopped, your cariprazine dose may need to be raised again.
- Report any new restlessness, tremor, stiffness, unusual movements, or heavy drowsiness.
Ask your pharmacist or prescriber before making any dosing change so they can tailor and monitor it safely.
Management is individual — confirm any change with your pharmacist or prescriber.
Literature reports
1 report — tap to read
a) In drug interaction studies, giving cariprazine 1.5 mg/day together with erythromycin (a moderate CYP3A4 inhibitor) 500 mg twice daily for 21 days led to an increase in cariprazine AUC (0 to 24 hours) and Cmax of roughly 50% 1. In one study that enrolled only White males taking cariprazine 1.5 mg/day and erythromycin 500 mg twice daily (n=40), the AUCs rose by 38% (cariprazine), 11% (desmethylcariprazine, an active metabolite), and 60% (didesmethylcariprazine, an active metabolite), while Cmax increased by 34%, 16%, and 62%, respectively. Tmax was not altered by concurrent administration with erythromycin 2.
Common questions
Can I take Diltiazem and Cariprazine together?
Diltiazem can raise cariprazine levels and side effect risk, so your care team will usually lower the cariprazine dose and monitor you. Keep taking both as prescribed and talk with your pharmacist or doctor about the right dose. Always confirm with your pharmacist or prescriber before making any change.
How serious is the Diltiazem 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 Diltiazem and Cariprazine interaction managed?
Keep taking both medicines exactly as prescribed unless your care team tells you otherwise. Because diltiazem raises cariprazine levels, your team typically manages this by using a lower cariprazine dose and watching how you respond. They may start or adjust cariprazine at a reduced dose (for example, taking it every other day rather than daily) and individualize it to you. If diltiazem is later s… 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 Diltiazem 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 (2)
- Product Information: VRAYLAR(R) oral capsules, cariprazine oral capsules. AbbVie Inc. (per FDA), North Chicago, IL, 2024. DailyMed
- Szabo M, Hujber Z, Harsanyi J, et al: Coadministration of cariprazine with a moderate CYP3A4 inhibitor in patients with schizophrenia: implications for dose adjustment and safety monitoring. Clin Pharmacokinet 2024; 63(10):1501-1510. PubMed
Keep reading about Diltiazem
Keep reading about Cariprazine
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