Drug interactions
Fluoxetine + Phentermine
Severity: Moderate
Fluoxetine and Phentermine: 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
Phentermine is a sympathomimetic with weak monoamine-releasing activity, and combining it with an SSRI has been associated with serotonin syndrome in case reports. The risk appears low but is potentially serious.
What this interaction means in plain words
Fluoxetine and Phentermine 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; Phentermine belongs to Central Nervous System.
Why it happens
Possible additive serotonergic and monoaminergic effects; mechanism not firmly established.
What to do
Counsel patients to report agitation, tremor, sweating, or palpitations. Monitor blood pressure and heart rate, and stop phentermine if serotonin toxicity is suspected.
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 Fluoxetine
- Fluoxetine + Isocarboxazid Contraindicated
- Fluoxetine + Mavacamten Contraindicated
- Fluoxetine + Methylene blue Contraindicated
- Fluoxetine + Phenelzine Contraindicated
- Fluoxetine + Pimozide Contraindicated
- Fluoxetine + Rasagiline Contraindicated
Other interactions of Phentermine
- Isocarboxazid + Phentermine Contraindicated
- Linezolid + Phentermine Contraindicated
- Phenelzine + Phentermine Contraindicated
- Phentermine + Procarbazine Contraindicated
- Phentermine + Rasagiline Contraindicated
- Phentermine + Selegiline Contraindicated
Frequently asked questions
Can I take Fluoxetine with Phentermine?
MediHelp rates the interaction as moderate. Fluoxetine and Phentermine 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. Phentermine is a sympathomimetic with weak monoamine-releasing activity, and combining it with an SSRI has been associated with serotonin syndrome in case reports. The risk appears low but is potentially serious.
How serious is the interaction between Fluoxetine and Phentermine?
MediHelp rates it moderate, on a four-level scale (minor, moderate, major, contraindicated) based on published labels and references. What to do, in brief: Counsel patients to report agitation, tremor, sweating, or palpitations. Monitor blood pressure and heart rate, and stop phentermine if serotonin toxicity is suspected.
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.
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