Drug interactions
Phentermine + Promethazine
Severity: Moderate
Phentermine and Promethazine: 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 stimulant, while promethazine is a sedating phenothiazine. Their central effects may offset each other, and both may contribute to tachycardia or rhythm disturbances in predisposed patients.
What this interaction means in plain words
Phentermine and Promethazine 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; Promethazine belongs to Respiratory.
Why it happens
Opposing CNS effects and possible additive cardiac effects; mechanism not firmly established.
What to do
Monitor heart rate, blood pressure and ECG in patients with cardiac risk factors. Reassess the need for promethazine if palpitations or arrhythmias occur.
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 Promethazine
- Ibutilide + Promethazine Contraindicated
- Pimozide + Promethazine Contraindicated
- Promethazine + Thioridazine Contraindicated
- Alfentanil + Promethazine Major
- Amiodarone + Promethazine Major
- Amisulpride + Promethazine Major
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 Promethazine?
MediHelp rates the interaction as moderate. Phentermine and Promethazine 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 stimulant, while promethazine is a sedating phenothiazine. Their central effects may offset each other, and both may contribute to tachycardia or rhythm disturbances in predisposed patients.
How serious is the interaction between Phentermine and Promethazine?
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 heart rate, blood pressure and ECG in patients with cardiac risk factors. Reassess the need for promethazine if palpitations or arrhythmias occur.
What other medicines interact with Promethazine?
MediHelp also lists interactions of Promethazine with, for example, Ibutilide, Pimozide, Thioridazine. The full list is on the Promethazine page.
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