Drug interactions
Phentermine + Thioridazine
Severity: Moderate
Phentermine and Thioridazine: 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 that can increase heart rate and blood pressure, while thioridazine prolongs the QT interval. The combination may increase the risk of arrhythmia, particularly in patients with cardiac risk factors.
What this interaction means in plain words
Phentermine and Thioridazine 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; Thioridazine belongs to Central Nervous System.
Why it happens
Sympathomimetic cardiovascular stimulation combined with thioridazine-induced QT prolongation; the stimulant also opposes sedation.
What to do
Avoid in patients with heart disease or known QT prolongation. Monitor heart rate, blood pressure and ECG if used together.
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 Thioridazine
- Abiraterone + Thioridazine Contraindicated
- Adagrasib + Thioridazine Contraindicated
- Amiodarone + Thioridazine Contraindicated
- Amisulpride + Thioridazine Contraindicated
- Amitriptyline + Thioridazine Contraindicated
- Amoxapine + Thioridazine 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 Thioridazine?
MediHelp rates the interaction as moderate. Phentermine and Thioridazine 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 that can increase heart rate and blood pressure, while thioridazine prolongs the QT interval. The combination may increase the risk of arrhythmia, particularly in patients with cardiac risk factors.
How serious is the interaction between Phentermine and Thioridazine?
MediHelp rates it moderate, on a four-level scale (minor, moderate, major, contraindicated) based on published labels and references. What to do, in brief: Avoid in patients with heart disease or known QT prolongation. Monitor heart rate, blood pressure and ECG if used together.
What other medicines interact with Thioridazine?
MediHelp also lists interactions of Thioridazine with, for example, Abiraterone, Adagrasib, Amiodarone. The full list is on the Thioridazine page.
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