What Is Folic Acid Used For? 5 Proven Medical and Nutritional Uses

Folic acid is used mainly to prevent neural tube defects (NTDs) in pregnancy, to treat anemia caused by folate deficiency, to reduce side effects of low-dose methotrexate, and to fortify enriched grain foods.¹²³⁴ It is also the form of vitamin B9 found in most multivitamins and prenatal vitamins.⁵

This page covers each use, who it applies to, how strong the evidence is, and which popular uses are not supported. Doses differ by use, so they are kept separate here.

Folic acid uses at a glance

These are separate indications. A prenatal dose, an anemia treatment dose, and folate support during methotrexate should not be combined into one generic "folic acid dosage."²³⁷

1. Preventing neural tube defects

This is the strongest and most actionable use of folic acid.¹⁶ NTDs happen when the embryo's neural tube fails to close correctly. They include spina bifida, anencephaly, and encephalocele, and USPSTF estimates they affect about 3,000 U.S. pregnancies a year.⁶

Average risk

CDC recommends 400 mcg of folic acid daily for all women who could become pregnant, from supplements, fortified foods, or both, in addition to a varied diet.⁸¹ USPSTF gives an A recommendation to a daily supplement of 400 to 800 mcg, starting at least one month before conception and continuing through the first two to three months of pregnancy.⁶⁹

The neural tube normally closes about 26 to 28 days after fertilization, often before pregnancy is recognized, which is why the advice starts before conception.⁹¹⁰ CDC states that folic acid is the only form of folate shown in studies to help prevent NTDs.¹¹ Our guide to folic acid for pregnancy covers timing and choosing a prenatal.

Higher risk

After a previous NTD-affected pregnancy, CDC recommends 4,000 mcg (4 mg) daily, starting one month before conception and continuing through the first three months. This is a medical dose above the normal upper limit and should be coordinated with a clinician.¹¹¹

2. Treating folate-deficiency anemia

Folic acid treats megaloblastic anemia caused by folate deficiency.² When folate is short, DNA formation is disrupted and the body makes large, immature red blood cells, which can cause fatigue, weakness, headache, palpitations, and shortness of breath.⁵

Treatment has two parts: giving folic acid and fixing the cause, such as a poor diet, alcohol use, malabsorption, or a medicine that interferes with folate.²¹³ Causes and risk groups include low intake, alcohol use disorder, celiac disease, inflammatory bowel disease, bariatric surgery, and increased needs in pregnancy.⁶⁵

Read more about symptoms and causes in our guide to folic acid deficiency.

3. Reducing methotrexate side effects

Methotrexate works against folate pathways. In low-dose treatment for inflammatory conditions such as rheumatoid arthritis or psoriasis, prescribed folic acid can reduce stomach, mouth, liver-enzyme, and other side effects without meaningfully weakening the treatment in standard regimens.¹⁴³

A common U.K. regimen is 5 mg of folic acid once a week, on a different day from methotrexate, sometimes adjusted by the prescriber.³ Regimens vary by country, condition, methotrexate dose, kidney function, and specialist protocol, so follow your exact prescription rather than a schedule found online.³

High-dose methotrexate used for cancer or other indications follows different rules. Oncology "rescue" uses folinic acid (leucovorin) on precise schedules, and folic acid is not a substitute for it.⁷¹⁵ Do not add an over-the-counter folic acid product to prescribed folate without checking with your prescriber.¹⁶⁷ See methotrexate and folic acid for more.

4. Fortifying the food supply

Since 1998, the U.S. has required folic acid to be added to specified enriched cereal grain products at 140 mcg per 100 g, including many enriched breads, flours, cereals, rice, pasta, and cornmeal products.⁴⁵ FDA also permits voluntary fortification of corn masa flour.⁴

CDC estimates fortification prevented about 1,300 NTD-affected births per year, with NTD prevalence falling about 35%.¹⁷¹⁸ Fortification complements the supplement recommendation for people who could become pregnant; it does not replace it.¹⁷¹⁸

5. Meeting everyday folate needs

Folic acid is included in multivitamins, B-complex products, and prenatal vitamins to help people meet their daily folate needs. Common adult amounts are 400 to 800 mcg of folic acid.⁵ The adult RDA is 400 mcg DFE per day, rising to 600 mcg DFE in pregnancy and 500 mcg DFE while breastfeeding.⁵

On U.S. labels, the Daily Value for folate is 400 mcg DFE for adults and children aged 4 and older, and a product with 20% or more of the Daily Value per serving counts as a high source.⁵ A balanced diet can meet the adult RDA, especially with fortified foods.¹⁵ For people who do not eat enough folate-rich or fortified foods, a supplement is one way to close the gap.⁸

How folic acid is usually taken

For routine use, folic acid is simple. There is no established clinical advantage to taking it in the morning or at night; taking it consistently matters more.³⁵ It can generally be taken with or without food, and taking it with food can be easier if it causes nausea.¹⁹⁵

Side effects are uncommon at usual doses. Minor effects can include nausea, reduced appetite, gas, or bloating, while severe allergic symptoms, trouble breathing, or swelling need urgent care.¹⁹ CDC states that 400 mcg a day has not been shown to cause harm.²⁰

The adult upper limit is 1,000 mcg a day of folic acid from supplements and fortified foods, and taking more than recommended is not known to improve NTD protection for average-risk people.⁵²¹

Uses that are not supported by evidence

Many claims online go further than the research. Here is how the evidence grades out.⁵²⁰

For a fuller look at each outcome, see folic acid benefits. For how folate works inside cells, see what folic acid does.

Who should check with a clinician first

Some people should not start or change folic acid without individual advice.⁶⁵

• People taking methotrexate, antiseizure medicines (phenytoin, carbamazepine, valproate), sulfasalazine, trimethoprim, or cancer therapy.³⁵²²
• Anyone with a previous NTD-affected pregnancy or a family history of NTDs.⁶¹
• People with unexplained anemia or suspected B12 deficiency.²³¹³
• Anyone planning to take more than 1,000 mcg a day outside an established clinical plan.⁵

Always tell your clinician and pharmacist about vitamins and supplements you take, since "it is only a vitamin" is not a safe interaction rule.²⁴

This article is for general education and is not medical advice. Doses and needs differ from person to person, so talk with your clinician or pharmacist about your situation. Read our editorial policy and medical disclaimer.