Is Folic Acid Safe with phenytoin?
Free · No account · based on published sources including NIH ODS, FDA drug labels, and peer-reviewed literature
Consult your doctor before taking folic acid supplements while on phenytoin. Monitor phenytoin serum levels if folic acid is added or withdrawn from your regimen.
Why this interaction occurs
Folic acid is listed as an agent that may decrease phenytoin serum levels. Addition or withdrawal of folic acid in patients on phenytoin therapy may require a dose adjustment of phenytoin to achieve optimal clinical outcome.
Evidence
Evidence level: strong.
Data source
FDA Drug Label
Reported safety data
The FDA’s adverse event reporting system (FAERS) has received 25,235 reports mentioning phenytoin. This reflects reported cases involving the medication in general — not confirmed causation, and not specific to the phenytoin + supplement combination on this page.
FAERS reports are voluntary and cannot prove that a drug caused an event. Do not use report counts to assess the safety of this specific drug-supplement pair.
Frequently asked questions
Related interactions
All Folic Acid interactions → · All phenytoin interactions →
Already checked this one — check your whole list
Educational only — not medical advice.
Always confirm with your doctor or pharmacist.