Drug interactions
Fluoxetine + Morphine
Severity: Moderate
Fluoxetine and Morphine: 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
Fluoxetine may rarely contribute to serotonin toxicity with opioids. It inhibits CYP2D6, but morphine is mainly glucuronidated, so the pharmacokinetic effect is small and clinically minor.
What this interaction means in plain words
Fluoxetine and Morphine 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.
Fluoxetine belongs to Central Nervous System; Morphine belongs to Musculoskeletal.
Why it happens
Possible additive serotonergic effects; CYP2D6 inhibition has little relevance since morphine is cleared mainly by glucuronidation.
What to do
Usually acceptable; monitor for serotonin toxicity and for changes in analgesia. Stop and treat supportively if serotonin syndrome develops.
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?
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Other interactions of Morphine
- Alvimopan + Morphine Contraindicated
- Isocarboxazid + Morphine Contraindicated
- Morphine + Olanzapine / samidorphan Contraindicated
- Morphine + Phenelzine Contraindicated
- Morphine + Tranylcypromine Contraindicated
- Alfentanil + Morphine Major
Other interactions of Fluoxetine
- Fluoxetine + Isocarboxazid Contraindicated
- Fluoxetine + Mavacamten Contraindicated
- Fluoxetine + Methylene blue Contraindicated
- Fluoxetine + Phenelzine Contraindicated
- Fluoxetine + Pimozide Contraindicated
- Fluoxetine + Rasagiline Contraindicated
Frequently asked questions
Can I take Fluoxetine with Morphine?
MediHelp rates the interaction as moderate. Fluoxetine and Morphine 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. Fluoxetine may rarely contribute to serotonin toxicity with opioids. It inhibits CYP2D6, but morphine is mainly glucuronidated, so the pharmacokinetic effect is small and clinically minor.
How serious is the interaction between Fluoxetine and Morphine?
MediHelp rates it moderate, on a four-level scale (minor, moderate, major, contraindicated) based on published labels and references. What to do, in brief: Usually acceptable; monitor for serotonin toxicity and for changes in analgesia. Stop and treat supportively if serotonin syndrome develops.
What other medicines interact with Morphine?
MediHelp also lists interactions of Morphine with, for example, Alvimopan, Isocarboxazid, Olanzapine / samidorphan. The full list is on the Morphine page.
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