Drug interactions
Fluoxetine + Venlafaxine
Severity: Major
Fluoxetine and Venlafaxine: major interaction.
Last updated Sources: US FDA label
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
Both drugs raise serotonin levels, so combined use raises the risk of serotonin syndrome. Fluoxetine inhibits CYP2D6, which converts venlafaxine to its active metabolite, shifting the balance of effects and potentially increasing blood pressure and cardiac risk.
What this interaction means in plain words
Fluoxetine and Venlafaxine can interact in a way that may be serious. Using them together is sometimes necessary, but it needs a deliberate decision by the prescriber, a plan for monitoring, and clear advice on the warning signs to watch for.
Fluoxetine belongs to Central Nervous System; Venlafaxine belongs to Central Nervous System.
Why it happens
Additive serotonin reuptake inhibition with fluoxetine inhibition of CYP2D6 metabolism of venlafaxine.
What to do
Avoid the combination where possible; if necessary use low doses and monitor blood pressure and for serotonin toxicity. Cross-taper carefully when switching, allowing for fluoxetine's long half-life.
What to ask your pharmacist
- Does the benefit of taking both outweigh the risk in my case?
- Do I need any blood test, ECG or other check while on both?
- What early warning signs should I watch for, and what should I do if they appear?
Pro+ members
Unlock the full page
Create an account and start a Pro+ trial to unlock the full management advice for Fluoxetine and Venlafaxine, 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.
References
Other interactions of Fluoxetine
- Fluoxetine + Isocarboxazid Contraindicated
- Fluoxetine + Mavacamten Contraindicated
- Fluoxetine + Methylene blue Contraindicated
- Fluoxetine + Phenelzine Contraindicated
- Fluoxetine + Pimozide Contraindicated
- Fluoxetine + Rasagiline Contraindicated
Other interactions of Venlafaxine
- Isocarboxazid + Venlafaxine Contraindicated
- Methylene blue + Venlafaxine Contraindicated
- Phenelzine + Venlafaxine Contraindicated
- Procarbazine + Venlafaxine Contraindicated
- Rasagiline + Venlafaxine Contraindicated
- Safinamide + Venlafaxine Contraindicated
Frequently asked questions
Can I take Fluoxetine with Venlafaxine?
MediHelp rates the interaction as major. Fluoxetine and Venlafaxine can interact in a way that may be serious. Using them together is sometimes necessary, but it needs a deliberate decision by the prescriber, a plan for monitoring, and clear advice on the warning signs to watch for. Both drugs raise serotonin levels, so combined use raises the risk of serotonin syndrome. Fluoxetine inhibits CYP2D6, which converts venlafaxine to its active metabolite, shifting the balance of effects and potentially increasing blood pressure and cardiac risk.
How serious is the interaction between Fluoxetine and Venlafaxine?
MediHelp rates it major, on a four-level scale (minor, moderate, major, contraindicated) based on published labels and references. What to do, in brief: Avoid the combination where possible; if necessary use low doses and monitor blood pressure and for serotonin toxicity. Cross-taper carefully when switching, allowing for fluoxetine's long half-life.
What other medicines interact with Fluoxetine?
MediHelp also lists interactions of Fluoxetine with, for example, Isocarboxazid, Mavacamten, Methylene blue. The full list is on the Fluoxetine 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.
