Drug interactions
Cimetidine + Phenobarbital
Severity: Minor
Cimetidine and Phenobarbital: minor 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
Phenobarbital may induce enzymes that clear cimetidine and slightly reduce its effect. Cimetidine may raise phenobarbital levels. The overall impact is usually small.
What this interaction means in plain words
Cimetidine and Phenobarbital have a small, usually unimportant interaction. Most people can take both; the pharmacist may still mention it so that any unexpected effect is recognised.
Why it happens
Phenobarbital induces hepatic CYP enzymes; cimetidine inhibits CYP metabolism of phenobarbital.
What to do
No routine adjustment is needed; monitor for sedation and for phenobarbital levels if clinical changes occur.
What to ask your pharmacist
- Is there anything I should notice while taking both?
- Do I need to tell my doctor at the next visit?
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Other interactions of Cimetidine
- Cimetidine + Dofetilide Contraindicated
- Cimetidine + Fezolinetant Contraindicated
- Alfentanil + Cimetidine Major
- Atazanavir + Cimetidine Major
- Carmustine + Cimetidine Major
- Cimetidine + Citalopram Major
Frequently asked questions
Can I take Cimetidine with Phenobarbital?
MediHelp rates the interaction as minor. Cimetidine and Phenobarbital have a small, usually unimportant interaction. Most people can take both; the pharmacist may still mention it so that any unexpected effect is recognised. Phenobarbital may induce enzymes that clear cimetidine and slightly reduce its effect. Cimetidine may raise phenobarbital levels. The overall impact is usually small.
How serious is the interaction between Cimetidine and Phenobarbital?
MediHelp rates it minor, on a four-level scale (minor, moderate, major, contraindicated) based on published labels and references. What to do, in brief: No routine adjustment is needed; monitor for sedation and for phenobarbital levels if clinical changes occur.
What other medicines interact with Cimetidine?
MediHelp also lists interactions of Cimetidine with, for example, Dofetilide, Fezolinetant, Alfentanil. The full list is on the Cimetidine page.
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