Is Folic Acid (High-dose) Safe with Tamoxifen?
Free · No account · based on published sources including NIH ODS, FDA drug labels, and peer-reviewed literature
Avoid high-dose folic acid supplements (>800 mcg/day) during tamoxifen therapy unless prescribed. Inform your oncologist about all supplements including multivitamins containing folic acid.
Why this interaction occurs
High folic acid intake may promote proliferation of folate-sensitive cancer cell lines. Some breast cancer subtypes demonstrate folate receptor overexpression, and excessive supplementation could theoretically stimulate residual tumor cell growth, counteracting tamoxifen's antiproliferative effect.
Evidence
Evidence level: limited.
Reported safety data
The FDA’s adverse event reporting system (FAERS) has received 22,724 reports mentioning Tamoxifen. This reflects reported cases involving the medication in general — not confirmed causation, and not specific to the Tamoxifen + 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 (High-dose) interactions → · All Tamoxifen interactions →
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Educational only — not medical advice.
Always confirm with your doctor or pharmacist.