Drug interactions
Phentermine + Venlafaxine
Severity: Moderate
Phentermine and Venlafaxine: 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 releases catecholamines and has some serotonergic activity, and combined use with venlafaxine may raise the risk of serotonin syndrome and increase blood pressure and heart rate. Case-level evidence is limited.
What this interaction means in plain words
Phentermine and Venlafaxine 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 belongs to Central Nervous System; Venlafaxine belongs to Central Nervous System.
Why it happens
Additive monoaminergic and serotonergic effects; the exact mechanism is not firmly established.
What to do
Monitor blood pressure, heart rate and signs of serotonin toxicity, particularly after starting or changing doses. Consider another weight-loss option if cardiovascular or neuropsychiatric symptoms develop.
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 Venlafaxine
- Isocarboxazid + Venlafaxine Contraindicated
- Methylene blue + Venlafaxine Contraindicated
- Phenelzine + Venlafaxine Contraindicated
- Procarbazine + Venlafaxine Contraindicated
- Rasagiline + Venlafaxine Contraindicated
- Safinamide + Venlafaxine 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 Phentermine with Venlafaxine?
MediHelp rates the interaction as moderate. Phentermine and Venlafaxine 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 releases catecholamines and has some serotonergic activity, and combined use with venlafaxine may raise the risk of serotonin syndrome and increase blood pressure and heart rate. Case-level evidence is limited.
How serious is the interaction between Phentermine and Venlafaxine?
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 blood pressure, heart rate and signs of serotonin toxicity, particularly after starting or changing doses. Consider another weight-loss option if cardiovascular or neuropsychiatric symptoms develop.
What other medicines interact with Venlafaxine?
MediHelp also lists interactions of Venlafaxine with, for example, Isocarboxazid, Methylene blue, Phenelzine. The full list is on the Venlafaxine page.
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