RESEARCH MONOGRAPH · KDC-MN-186

L-Methylfolate (5-MTHF)

May 9, 2026 Kodiac biolabs Research Revised May 30, 2026 2 min read

Our opinion on this compound

80/100

The active folate that actually bypasses MTHFR variants, and the supplement market has finally caught up

L-methylfolate (also called 5-methyltetrahydrofolate or 5-MTHF) is the bioactive form of folate that's actually used in one-carbon metabolism for the methylation cycle. The dietary folates and synthetic folic acid all have to be converted through several enzymatic steps, with methylenetetrahydrofolate reductase (MTHFR) being the rate-limiting and genetically variable enzyme, to produce 5-MTHF, which is then the substrate that donates methyl groups for the conversion of homocysteine back to methionine via methionine synthase.

The MTHFR polymorphism story is the reason this matters. The C677T variant (and to a lesser extent A1298C) reduces MTHFR activity by anywhere from 30-70% in homozygotes, which means folic acid supplementation in those individuals doesnt efficiently produce 5-MTHF. The remaining folate sits as unmetabolized folic acid (UMFA), which has its own pharmacology (some immune-modulatory concerns at high chronic exposure) and doesnt do what you wanted it to do.

Supplementing 5-MTHF directly bypasses MTHFR entirely. So for the maybe 15-20% of the population with significant MTHFR variants (much higher in certain ethnicities), 5-MTHF supplementation is the form that actually corresponds to functional folate status. This is one of the cleanest examples of pharmacogenomics in nutritional supplementation.

Clinical signal for 5-MTHF specifically is real. There's a small but meaningful literature on 5-MTHF as an adjunct to SSRIs in depression (especially in MTHFR variants), peri-conceptional supplementation in women with MTHFR variants for neural tube defect prevention, and homocysteine reduction in cardiovascular populations. The 2012 Papakostas trial in SSRI-resistant depression used 15mg L-methylfolate daily and saw real adjunctive effects.

Sourcing matters because of stereochemistry. The biologically active form is specifically (6S)-5-methyltetrahydrofolate, with the (6R) isomer being inactive. Quatrefolic (the patented glucosamine salt of (6S)-5-MTHF, Gnosis) and Metafolin (calcium salt of (6S)-5-MTHF, Merck) are the validated isomerically-pure forms used in most clinical work. Generic 5-MTHF can sometimes be racemic, which dilutes the active dose.

Safety is generally fine. Watch for masking B12 deficiency the same way folic acid does, which is a real clinical concern.

What we like: the right form of the molecule for a meaningful chunk of the population, and the pharmacogenomic story is genuinely clear. What we dont like: a lot of generic 5-MTHF products dont specify isomeric purity, which matters.

Evidence: 75
Mechanism: 90
Reliability: 80
Safety: 85
Sourcing: 75
Value: 75
Signal: 75
Staying power: 82

Plain-language summary Intrigue 60 / 100

L-methylfolate (5-MTHF) is the active form of folate, bypassing the MTHFR enzyme that some patients have polymorphisms in. Used for depression augmentation (especially in MTHFR variants) and for pregnancy. Not stocked by Kodiac. This monograph is provided for research and educational reference.

Intrigue 0–100 blends mechanism novelty, evidence strength, and translational potential. Kodiac editorial, not peer-reviewed.

Active folate / 5-methyltetrahydrofolate

The active form of folate (5-methyltetrahydrofolate) used clinically for major depression adjunct and for individuals with MTHFR polymorphisms.

Abstract

L-Methylfolate (5-methyltetrahydrofolate, 5-MTHF; CAS 31690-09-2) is the active form of folate (vitamin B9), bypassing the methylenetetrahydrofolate reductase (MTHFR) step that is impaired in individuals with C677T or A1298C MTHFR polymorphisms. The compound is FDA-approved as Deplin (medical food) for major depressive disorder, particularly in patients with low folate status or MTHFR polymorphisms. Mechanism is provision of methyl groups for SAM-e synthesis and downstream methylation, including monoamine neurotransmitter synthesis. Reported research dose ranges in the literature are described in the source publications. clinical use for depression is at the high end (7.5 to 15 mg).

Mechanism of action

Active folate form; bypasses MTHFR step. Methyl group provision for SAM-e and neurotransmitter synthesis.

Reported research dose ranges

Reported research dose ranges in the literature.

References

Papakostas GI, et al. L-methylfolate as adjunctive therapy for SSRI-resistant major depression. Am J Psychiatry 2012.

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KDC-MN-186

The full reference document is provided strictly for research use only. It reports research dose ranges from the published literature, not instructions for use in humans or animals.

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FOR RESEARCH USE ONLY. Not for medical, diagnostic, or therapeutic purposes. Not for human consumption. All information is provided for research and educational purposes only.

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L-Methylfolate (5-MTHF)

Abstract

Mechanism of action

Reported research dose ranges

References

Read the full monograph

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Abstract

Mechanism of action

Reported research dose ranges

References

Read the full monograph

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