Drug interactions
Mirtazapine + Phenytoin
Severity: Moderate
Mirtazapine and Phenytoin: moderate interaction.
Last updated
For healthcare professionals — reference only. This page is a brief summary, not medical advice and not a substitute for official labeling or clinical judgement. Always verify before prescribing or dispensing.
Summary
Phenytoin is a strong inducer of CYP3A4 and other enzymes and can substantially lower mirtazapine concentrations, reducing antidepressant effect. Mirtazapine has little effect on phenytoin levels.
What this interaction means in plain words
Mirtazapine and Phenytoin can affect each other. The combination is often manageable, but it may need a change of dose, a change of timing, or extra checks while both are taken.
Mirtazapine belongs to Central Nervous System; Phenytoin belongs to Central Nervous System.
Why it happens
Induction of CYP3A4 and related enzymes by phenytoin increases mirtazapine clearance.
What to do
Monitor for loss of antidepressant response and increase the mirtazapine dose as needed. Reassess the dose and watch for increased mirtazapine effects if phenytoin is stopped.
What to ask your pharmacist
- Should I take them at different times of day?
- Does the dose of either medicine need to change?
- Is there anything I should avoid, such as alcohol or certain foods, while on both?
Pro+ members
Unlock the full page
Create an account and start a Pro+ trial to unlock the full management advice for Mirtazapine and Phenytoin, the additional notes, the evidence detail and the whole-prescription interaction checker.
- Full clinical management advice
- Additional notes
- Evidence detail
- Interaction checker for a whole prescription
Try Pro+ free for 7 days on the web. No card needed.
Other interactions of Mirtazapine
- Isocarboxazid + Mirtazapine Contraindicated
- Mirtazapine + Phenelzine Contraindicated
- Mirtazapine + Pimozide Contraindicated
- Mirtazapine + Procarbazine Contraindicated
- Mirtazapine + Rasagiline Contraindicated
- Mirtazapine + Selegiline Contraindicated
Other interactions of Phenytoin
- Artemether / lumefantrine + Phenytoin Contraindicated
- Bictegravir + Phenytoin Contraindicated
- Cabotegravir + Phenytoin Contraindicated
- Doravirine + Phenytoin Contraindicated
- Elbasvir / grazoprevir + Phenytoin Contraindicated
- Elvitegravir / cobicistat / emtricitabine / tenofovir df + Phenytoin Contraindicated
Frequently asked questions
Can I take Mirtazapine with Phenytoin?
MediHelp rates the interaction as moderate. Mirtazapine and Phenytoin can affect each other. The combination is often manageable, but it may need a change of dose, a change of timing, or extra checks while both are taken. Phenytoin is a strong inducer of CYP3A4 and other enzymes and can substantially lower mirtazapine concentrations, reducing antidepressant effect. Mirtazapine has little effect on phenytoin levels.
How serious is the interaction between Mirtazapine and Phenytoin?
MediHelp rates it moderate, on a four-level scale (minor, moderate, major, contraindicated) based on published labels and references. What to do, in brief: Monitor for loss of antidepressant response and increase the mirtazapine dose as needed. Reassess the dose and watch for increased mirtazapine effects if phenytoin is stopped.
What other medicines interact with Mirtazapine?
MediHelp also lists interactions of Mirtazapine with, for example, Isocarboxazid, Phenelzine, Pimozide. The full list is on the Mirtazapine page.
Full monographs, dosing and an interaction checker in the MediHelp app
Open the complete reference, check multi-drug interactions and use dosing tools in the MediHelp app.
