Vitamin B9 (5-Methyltetrahydrofolate)

vitamin5-methyltetrahydrofolate

What is it

5-Methyltetrahydrofolate (5-MTHF), also called methylfolate or L-methylfolate, is the biologically active form of vitamin B9 that circulates in blood and crosses cell membranes. It does not require enzymatic conversion before use.

How it works

5-MTHF serves as a methyl donor in the conversion of homocysteine to methionine, supporting DNA synthesis, neurotransmitter production, and the body's methylation reactions overall. Other B9 forms (folate from food, folic acid from supplements) must be converted through several enzymatic steps — including via the MTHFR enzyme — to become 5-MTHF. People with common MTHFR genetic variants (C677T, A1298C) have reduced conversion capacity. For them, supplementing with the already-converted 5-MTHF form theoretically bypasses the bottleneck. Whether this translates to better clinical outcomes for most people is debated.

Evidence for 4 uses

AI-assisted evidence assessment — talk to your doctor before relying on any single supplement.

Folate status in MTHFR variants

Grade B

Good evidence

People with reduced MTHFR enzyme activity convert less folic acid to active 5-MTHF. Taking 5-MTHF directly bypasses this step and can raise blood folate more effectively in these individuals.

Lowering homocysteine

Grade B

Good evidence

5-MTHF, like folic acid, reduces homocysteine. Cardiovascular benefit has not been consistently shown.

Depression adjunct (with antidepressants)

Grade C

Moderate evidence

L-methylfolate (typically 7.5 to 15 mg/day) has shown modest benefit as an add-on to SSRIs in some trials, particularly in people with folate deficiency or MTHFR variants.

Pregnancy and neural tube defects

Grade C

Moderate evidence

5-MTHF likely provides similar protection as folic acid, but the bulk of trial evidence is for folic acid. Many prenatal vitamins now include methylfolate.

Dosage

Common supplement doses are 400 to 1,000 mcg of 5-MTHF, comparable to folic acid doses. Prescription L-methylfolate for depression adjunct therapy is typically 7.5 to 15 mg per day. The general upper limit for folate from supplements is 1,000 mcg per day, though prescription doses for specific conditions exceed this under medical supervision.

When and how to take it

5-MTHF can be taken any time of day with or without food. Consistent daily dosing matters more than timing. For pregnancy preparation, start at least a month before conception.

Safety

5-MTHF is well tolerated. Unlike folic acid, it does not cause accumulation of unmetabolized folic acid in the blood — a concern some researchers have raised, though the clinical significance is unclear. The same caution about masking B12 deficiency applies: high-dose folate of any form can correct B12-deficiency anemia while neurological damage progresses.

Who should be cautious

People with MTHFR variants who want to take a folate supplement may prefer 5-MTHF. Pregnant women using methylfolate for neural tube defect prevention can do so, though most clinical trials and guidelines use folic acid. People taking methotrexate should follow specific prescriber instructions. Older adults should still confirm B12 status before high-dose use.

Interactions

Same as other B9 forms. Methotrexate, anticonvulsants, sulfasalazine, and trimethoprim affect folate metabolism. 5-MTHF interacts with some psychiatric medications when used at high prescription doses — coordinate with prescribers.

Frequently asked questions

Should I take methylfolate instead of folic acid?⌄

If you have a known MTHFR variant or prefer to avoid unmetabolized folic acid, methylfolate is a reasonable choice. For most people without those concerns, folic acid works fine and is cheaper.

Is methylfolate better for pregnancy?⌄

It likely provides similar protection against neural tube defects, but folic acid has the longest track record and is what most guidelines specifically recommend.

Can methylfolate help depression?⌄

Prescription L-methylfolate at higher doses (7.5 to 15 mg) has shown modest benefit as an antidepressant adjunct in some trials, especially for people with folate deficiency or MTHFR variants.

How much methylfolate should I take?⌄

For general supplementation, 400 to 1,000 mcg per day. Higher prescription doses are used for specific medical indications under physician guidance.

Do I need to take methylfolate if I have MTHFR variants?⌄

Many providers recommend it, but the clinical importance of common MTHFR variants in otherwise healthy people is debated. It is a reasonable choice but not strictly necessary for everyone.

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Disclaimer: These statements have not been evaluated by the FDA. This page is educational, not a substitute for personalized medical advice. Evidence grades are AI-assisted assessments — talk to your doctor before starting any new supplement, especially if you're pregnant, breastfeeding, on medications, or managing a chronic condition.