Drug interactions
Cyproheptadine + Promethazine
Severity: Moderate
Cyproheptadine 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
Both drugs are sedating first-generation antihistamines with anticholinergic activity. Taken together they can cause excessive drowsiness, impaired psychomotor performance and greater anticholinergic effects such as dry mouth, urinary retention and confusion, particularly in older adults.
What this interaction means in plain words
Cyproheptadine 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.
Cyproheptadine belongs to Respiratory; Promethazine belongs to Respiratory.
Why it happens
Additive central H1-receptor antagonism and muscarinic blockade.
What to do
Avoid combining two sedating antihistamines where possible; if both are needed, use the lowest doses and monitor for oversedation and anticholinergic toxicity. Warn patients against driving or operating machinery.
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
- Cabergoline + Promethazine Contraindicated
- Dopamine + Promethazine Contraindicated
- Ibutilide + Promethazine Contraindicated
- Pimozide + Promethazine Contraindicated
- Promethazine + Thioridazine Contraindicated
- Alfentanil + Promethazine Major
Other interactions of Cyproheptadine
- Cyproheptadine + Isocarboxazid Contraindicated
- Cyproheptadine + Phenelzine Contraindicated
- Cyproheptadine + Tranylcypromine Contraindicated
- Alfentanil + Cyproheptadine Major
- Belladonna and opium + Cyproheptadine Major
- Benzhydrocodone / acetaminophen + Cyproheptadine Major
Frequently asked questions
Can I take Cyproheptadine with Promethazine?
MediHelp rates the interaction as moderate. Cyproheptadine 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. Both drugs are sedating first-generation antihistamines with anticholinergic activity. Taken together they can cause excessive drowsiness, impaired psychomotor performance and greater anticholinergic effects such as dry mouth, urinary retention and confusion, particularly in older adults.
How serious is the interaction between Cyproheptadine 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: Avoid combining two sedating antihistamines where possible; if both are needed, use the lowest doses and monitor for oversedation and anticholinergic toxicity. Warn patients against driving or operating machinery.
What other medicines interact with Promethazine?
MediHelp also lists interactions of Promethazine with, for example, Cabergoline, Dopamine, Ibutilide. The full list is on the Promethazine page.
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