Folate

Folic acid · Vitamin B9 · Folate supplementation · Folic acid supplementation · Pteroylglutamic acid

Snapshot

Indications	Contraindications
Neural tube defect prevention¹ Folate deficiency² Adjunct for depression²	Untreated vitamin B12 deficiency² Methotrexate for cancer² Antifolate antimalarial therapy³

Folate is a water-soluble B vitamin found in foods, added to fortified grains, and sold as supplements; folic acid is the form in fortified foods and most products². It works as a coenzyme in one-carbon transfers for nucleic acid synthesis and homocysteine metabolism². People take it to prevent neural tube defects (NTDs), to correct low intake, and for stroke prevention, homocysteine lowering, and depression adjunct use.² Women who could become pregnant are the typical patient².

Evidence is strongest for NTD prevention, where guidelines endorse supplementation starting before conception¹. B-vitamin supplementation including folic acid shows preventive benefit for stroke. In a 2025 pair of prospective cohorts spanning mandatory fortification, higher red cell folate tracked with more gestational diabetes; no trial has tested this. Many products list folate, as folic acid or methylated folate; see Form comparison.

The main caution is vitamin B12: large folate intakes correct megaloblastic anemia but not the neurological damage of B12 deficiency². Per the National Institutes of Health fact sheet, patients taking methotrexate for cancer are told to consult their oncologist before supplementing².

Last updated October 16, 2026. Read how we make monographs.

In the full monograph

81 sources, 69 studies

When to useThe situations practitioners use it for, each with the reason and the study behind it.
SafetyWho should avoid it, who needs extra care, and the side effects reported in studies.
InteractionsThe medicines and supplements it interacts with, the effect of each, and what labeling says to watch.
Protocol notesThe doses used in studies, how and when they were taken, and how the forms on the market compare.
How it worksWhat it is and how it works in the body, in plain terms.
Published studiesThe studies behind each use, popular claims checked against them, and trials still under way.
Word of mouthWhat patients and practitioners report online, kept separate from the clinical evidence.
Clinical perspectiveA closing read of where the evidence is solid, where it is thin, and what has not been studied.

Snapshot

In the full monograph

Sources