Genetic Testing in Psychiatry · Section D · Chapter 8 · What not to act on
Should an MTHFR Result Change Treatment?
Patients arrive with an MTHFR result — from a pharmacogenomic panel, a direct-to-consumer kit, or a functional-medicine workup — and a question: does it change my treatment? This chapter keeps two questions strictly apart and names the source for each. First: does an MTHFR genotype (C677T, A1298C) change psychiatric treatment? Second, and independently: is L-methylfolate (or folic acid) an evidence-based treatment, for whom and how strong is the evidence? A finding on one question never answers the other, and no body’s statement is presented as another’s.
The 30-second version
- Keep the two questions apart. (a) Does the MTHFR genotype change treatment? (b) Is folate worth using as a treatment? Different sources answer each. A genotype result does not establish that folate will help, and folate’s evidence does not make the genotype actionable.
- The genotype does not change psychiatric treatment. No FDA psychotropic drug label names MTHFR; it is absent from the FDA Table of Pharmacogenetic Associations and appears in the FDA Biomarkers table only once, for betaine in homocystinuria — a rare inborn error, not the common C677T/A1298C variants [11]. CPIC has no MTHFR guideline; MTHFR appears only as provisional gene–drug pairs (carboplatin, l-methylfolate, methotrexate) with no recommendation [12]. DPWG does cover MTHFR, but only for folic acid (“no action required”) and methotrexate (“not a gene–drug interaction”) — neither a psychotropic [13].
- A genotype is not a measured deficiency. C677T/A1298C predicts modestly reduced enzyme activity, not a folate or B12 deficiency and not an elevated homocysteine in any given patient [19]. The variants are common — more people in the U.S. carry C677T than do not — and at the same folic-acid intake a TT genotype gives blood folate only about 16% lower than CC [18]. Where there is a clinical reason, measure the biochemical state and act on that.
- Folate as a treatment is decided on clinical grounds, and L-methylfolate is not folic acid. For adjunctive L-methylfolate in SSRI-resistant major depression (partial or no response to an SSRI), Papakostas ran two sequential parallel-comparison trials: the first (7.5 mg/day, one arm stepping to 15 mg in the second period) was negative and the second (15 mg/day throughout) positive, NNT about 6 [2]; one review calls the methylfolate evidence “primarily positive” and supportive of adjunctive use [3], while the most recent review puts the effect as small/modest (RR 1.25) [4], and guideline bodies grade it a weak or second-line adjunct [5][6]. Folic acid is weaker still — nonsignificant in meta-analysis and negative in a dedicated trial [3][8]. L-methylfolate is marketed as a medical food; FDA says medical foods are not drugs [10].
- Say what the evidence does not show. No trial has compared genotype-guided folate treatment with the same treatment chosen without the genotype; the one genotype-selected RCT enrolled only MTHFR-positive patients, tested a reduced-B-vitamin combination rather than L-methylfolate alone, and had no genotype-negative arm [9]. For SLC6A4/HTR2A/ANK3 see Chapter 9; for reading a vendor report, Chapter 3; for whether to order a panel at all, Chapter 1.
At the visit: a patient with an MTHFR result
About 2 min to read · the detailed sections follow below
Do now
- Decide which question the patient is really asking: does the genotype change the plan, or should we use folate? Answer them separately.
- For the genotype: explain that no FDA psychotropic label, CPIC guideline or DPWG action makes an MTHFR genotype a basis for choosing or dosing a psychiatric drug [11][12][13].
- If there is a clinical reason to suspect deficiency, order serum B12 and/or folate by indication (MMA for an equivocal B12; homocysteine nonspecific) and act on the measurement, not the genotype.
- If considering folate as a treatment, weigh the actual trial evidence and the medical-food status, independent of the MTHFR result, and keep L-methylfolate and folic acid distinct [2][3][10].
- Document the discussion, what was and was not changed, and why.
Do not
- Change or add a psychiatric treatment on the basis of an MTHFR genotype alone.
- Treat an MTHFR genotype as if it were a measured folate, B12 or homocysteine abnormality.
- Let folate’s (modest) depression evidence stand in for the genotype being actionable, or the genotype stand in for a decision to use folate.
- Present a vendor report’s MTHFR interpretation, or a product label’s MTHFR wording, as an FDA, CPIC or DPWG recommendation [22].
- Repeat MTHFR genotyping — the germline result does not change, so re-testing adds nothing.
Does the genotype change treatment? — No
- No FDA/CPIC/DPWG action ties an MTHFR genotype to a psychotropic. Read the result for context and change nothing on the genotype [11][12][13].
Is there a biochemical abnormality to treat?
- If clinically indicated, order serum B12 and/or folate by indication (MMA for an equivocal B12; homocysteine nonspecific); treat a confirmed deficiency on its own merits, not as a genotype action.
Is folate a reasonable treatment here?
Decide on the trial evidence and the clinical picture, not the MTHFR result; note L-methylfolate’s medical-food status and its modest, mixed evidence — and that folic acid is weaker still [2][4][8][10].
Prescriber-side triage for an MTHFR result. Our synthesis of the sources cited below, not a validated instrument.
Which question are you answering?
Tap a question for what the sources say and what to do.
Genotype
Measure
Folate
Does the genotype change treatment?
No change on the genotypeNo named body ties an MTHFR genotype to a psychiatric drug choice or dose.
What the sources say
- No FDA psychotropic label names MTHFR; absent from the FDA Pharmacogenetic Associations table; in the Biomarkers table only for betaine in homocystinuria [11]
- CPIC: no MTHFR guideline; only provisional pairs, no recommendation [12]
- DPWG: covers MTHFR for folic acid and methotrexate only — not a psychotropic [13]
- Psychiatry panels list MTHFR among genes lacking sufficient evidence [16]; a commercial panel nonetheless called it “actionable” [17]
What to do
- Read the result for context; change nothing on the genotype (Chapter 1, Chapter 3)
- Do not repeat MTHFR genotyping — a germline result does not change
- Do not change a regimen on a test not supported by evidence [14]
Is there a biochemical abnormality?
Measure, don’t genotypeA genotype predicts an enzyme; it does not establish a folate/B12 deficiency or an elevated homocysteine in this patient.
What the sources say
- Polymorphisms can mildly raise homocysteine; homozygotes may have mild/moderate hyperhomocysteinemia of uncertain significance [1][19]
- The variants are common; TT blood folate is only ~16% lower than CC at the same intake; A1298C alone: insufficient evidence [18]
What to do
- If clinical features suggest deficiency, order serum B12 and/or folate by clinical indication rather than a reflex MTHFR-driven panel — methylmalonic acid to clarify an equivocal B12, homocysteine where it helps (nonspecific, rising with either deficiency) — and act on the measurement
- ACMG separately allows a fasting homocysteine in a thermolabile (C677T) homozygote to inform counseling; no held source gives a treatment cutoff [1]
- Treat a measured deficiency on its own merits
Is folate a reasonable treatment?
A separate questionWhether to use L-methylfolate is a treatment decision based on trial evidence and the clinical picture — not on the MTHFR result. L-methylfolate is not folic acid.
What the sources say
- L-methylfolate, adjunctive in SSRI-resistant MDD: Papakostas trial 1 (7.5 mg) negative, trial 2 (15 mg) positive, NNT ~6 [2]; “primarily positive”/supports use [3]; small/modest effect, RR 1.25 [4]; weak / second-line in guidelines [5][6]
- Folic acid: nonsignificant in meta-analysis [3]; negative in a dedicated trial [8]
- Marketed as a medical food; FDA: medical foods are not drugs [10]; product labels vary on MTHFR [22]
What to do
- Decide on the evidence and the clinical picture; do not justify it by the MTHFR genotype
- Keep L-methylfolate and folic acid distinct
- Stay commercial-neutral — do not endorse a product or lab
The two questions, with the source for each
Every row names its source separately. Where no body ties an action to the MTHFR genotype, that is the answer — and one body’s statement is never read as another’s.
| Question / item | What the named source says | Source |
|---|---|---|
| MTHFR in the FDA tables and labels | MTHFR is absent from the FDA Table of Pharmacogenetic Associations (current 09/10/2026). It appears once in the FDA Table of Pharmacogenomic Biomarkers — the betaine row, for homocystinuria (MTHFR deficiency), a rare inborn error, not C677T/A1298C. A review of current FDA drug labels for the major psychotropic, antiepileptic and antifolate drugs (including SSRIs, SNRIs, antipsychotics, lithium, methotrexate and pemetrexed) found none naming MTHFR. | FDA tables; openFDA [11] |
| MTHFR in CPIC | CPIC has 29 published guidelines; none is for MTHFR. MTHFR appears only as three provisional gene–drug pairs (carboplatin, l-methylfolate, methotrexate), none scored for a recommendation. The CPIC SSRI guideline covers CYP2D6/2C19/2B6/SLC6A4/HTR2A — not MTHFR. | CPIC / ClinPGx API [12] |
| MTHFR in DPWG | DPWG does have an MTHFR guideline, but only for folic acid (“NO action is required… 677CT has no effect… 677TT either has no effect or a positive effect”) and methotrexate (“this is NOT a gene–drug interaction”). Neither concerns a psychotropic or L-methylfolate. | DPWG (van der Pol 2024); ClinPGx [13] |
| ACMG position (scope matters) | ACMG (2013, reaffirmed 2020 and reclassified a Clinical Practice Resource) addresses MTHFR testing for thrombophilia, recurrent pregnancy loss and at-risk relatives — not psychiatric treatment. It states “there is currently no evidence that specific treatments reduce risks associated with hyperhomocysteinemia or MTHFR genotype status.” RACGP similarly finds routine MTHFR testing unlikely to change management. | ACMG 2013/2020 [1]; RACGP [21] |
| Psychiatry-panel context | MTHFR is “commonly appearing on psychiatry test panels that lack sufficient evidence or expert developed guidelines” [16]; a commercial pharmacogenetic tool nonetheless treated MTHFR as one of several non-CYP genes it classified “actionable,” without a validated MTHFR-based prescribing recommendation [17]. AACAP (2020) advises clinicians avoid pharmacogenetic testing to select psychotropics in youth; CANMAT (2023) does not recommend routine PGx testing — neither statement names MTHFR. | Bousman 2022 [16]; Zeier 2018 [17]; AACAP [15]; CANMAT [5] |
| L-methylfolate as a treatment (status) | Marketed as a medical food. FDA: “Medical foods are not drugs…”; there is “no requirement for a prescription” and labeling “may not bear the symbol ‘Rx only.’” The FDA guidance says nothing about L-methylfolate, folate or MTHFR. Product labels disagree on MTHFR (one “indicated regardless of MTHFR C677T… genotype”, another “for patients with… MTHFR”, an older one warning against use with an MTHFR mutation). None of this is an FDA/CPIC/DPWG recommendation. | FDA Medical Foods FAQ; 21 CFR 101.9(j)(8) [10]; DailyMed labels [22] |
| L-methylfolate trial evidence (MDD) | Papakostas 2012 (SSRI partial/non-responders): two sequential parallel-comparison trials; trial 1 (n=148, 7.5 mg/day, one arm stepping to 15 mg in the second period) “no significant difference”; trial 2 (n=75, 15 mg/day throughout) “significantly greater efficacy… on both primary outcome measures”, NNT ≈6. Sarris 2016: methylfolate “primarily positive” and supports adjunctive use. Maruf 2022 (most recent review): “small effect” (RR 1.25, 95% CI 1.08–1.46), “modest efficacy”, “rarely included in major clinical practice guidelines”. WFSBP/CANMAT 2022: methylfolate “Weakly Recommended” (+). CANMAT 2023: a second-line adjunctive option for mild-to-moderate major depressive episodes, with “small effect sizes” (Table 3.7). No abstract mentions MTHFR. (Beyond depression, the WFSBP/CANMAT 2022 taskforce provisionally recommends methylfolate (++) for negative symptoms in schizophrenia — a separate treatment-evidence question, not an MTHFR-guided indication.) | Papakostas 2012 [2]; Sarris 2016 [3]; Maruf 2022 [4]; Sarris 2022 [6]; CANMAT 2023 [5] |
| Folic acid as a treatment (kept separate) | Folic acid is a different compound. Sarris 2016: “a meta-analysis of folic acid revealed a nonsignificant difference from placebo.” FolATED (folic acid 5 mg): “no evidence that folic acid was clinically effective…”. Cochrane (folic acid or 5-MTHF, 3 trials, 247 people): “limited available evidence”. | Sarris 2016 [3]; FolATED [8]; Cochrane CD003390 [7] |
The detail: genotype is not biochemistry, and what the evidence does and does not show
MTHFR C677T and A1298C are common polymorphisms — ACMG estimates >25% of Hispanics and 10–15% of North American Caucasians are homozygous for the “thermolabile” C677T variant [1], and CDC notes more people in the U.S. carry C677T than do not [18]. They can modestly reduce enzyme activity and mildly raise homocysteine, “usually to a mild or moderate degree of uncertain clinical significance” [1][19]. None of the held sources gives a residual enzyme-activity percentage or a homocysteine treatment cutoff, so this chapter states none. A1298C alone has “insufficient evidence” to say it significantly affects folate processing [18]. The actionable quantity, where there is any, is the measured biochemical state — not the genotype.
What the evidence does not show: no trial has compared folate treatment chosen because of an MTHFR genotype against the same treatment chosen without it. The one genotype-selected RCT (Mech & Farah 2016, n=330) enrolled only patients positive for C677T or A1298C, tested a reduced-B-vitamin combination as monotherapy (not L-methylfolate alone), and had no genotype-negative comparison arm; its registry entry was submitted after the stated completion date and is titled a “post hoc analysis” [9]. So the claim is not “no genotype trial exists” but “the one that exists cannot test whether the genotype should guide treatment.”
A note for the prescriber on antifolate drugs (not psychotropics): bodies disagree and must be cited separately. ACMG (2013) advised telling a physician of MTHFR status before folate-dependent chemotherapy such as methotrexate [1]; DPWG (2022/2024) concluded MTHFR–methotrexate is “NOT a gene–drug interaction” [13]. Neither is a psychiatric drug, and no FDA methotrexate or pemetrexed label names MTHFR [11].
Does this apply to my patient?
Answer the genotype question and the treatment question separately; act on a measured abnormality, not on the genotype.
| Patient | What changes | Source |
|---|---|---|
| Brings an MTHFR report and asks to change or add treatment | No change on the genotype; explain why, read the result for context, do not re-test, and document [11][12][13] | FDA/CPIC/DPWG (no psychotropic action) [11][12][13] |
| Clinical features suggesting folate or B12 deficiency | Order serum B12 and/or folate by indication (MMA for an equivocal B12; homocysteine nonspecific); treat a confirmed deficiency on its own merits | General clinical practice |
| SSRI-resistant depression, considering adjunctive folate | Weigh the L-methylfolate evidence and medical-food status; decide on clinical grounds, not the genotype; L-methylfolate is not folic acid [2][4][10] | Papakostas; Maruf; FDA [2][4][10] |
| Could become pregnant; asks whether MTHFR changes folic acid | No. USPSTF: 0.4–0.8 mg folic acid daily for anyone who could become pregnant [20]; CDC: the same applies with an MTHFR variant, and the “avoid folic acid, take 5-MTHF” claim is not true [18]; ACMG: MTHFR status does not change the folic-acid recommendation [1] | USPSTF [20]; CDC [18]; ACMG [1] |
| Stable, effective, tolerated regimen | Do not change it on the basis of an MTHFR genotype | Chapter 1 |
Clinical pearls
- Two questions, two sources.“Does the genotype change treatment?” and “should I use folate?” are answered by different evidence — never let one answer the other.
- A genotype is not a lab value.MTHFR C677T/A1298C predicts an enzyme, not a measured folate, B12 or homocysteine result [19].
- No named body makes it a psychotropic action.No FDA psychotropic label, CPIC guideline or DPWG action ties MTHFR to a psychiatric drug; DPWG covers only folic acid and methotrexate [11][12][13].
- Cite each body for its own scope.ACMG speaks to thrombophilia and pregnancy loss, not psychiatry [1]; a product label’s MTHFR wording is not a guideline [22].
- L-methylfolate is not folic acid.Its (modest) adjunctive evidence stands on its own, graded weak/second-line; folic acid is weaker still [2][4][5][8].
- Measure when there is a reason.If deficiency is plausible, check the biochemical state and act on that.
- Stay commercial-neutral.Explain the result without endorsing a product or lab.
Patient script & EMR note
Counseling script: an MTHFR result that does not change treatment
“This result looks at a gene called MTHFR. It’s a very common variant — more people have it than don’t — and on its own it doesn’t tell me to change your medicine. The groups that set prescribing guidance don’t use it to pick a psychiatric drug.
What it is not is a measurement of your folate or B12. If there’s a reason to think those are low, I can check them with a blood test and treat what we actually find.
If you’re asking specifically about a folate supplement, that’s a separate question — I’d weigh it on the evidence for the supplement itself, not on this gene result. And if pregnancy is on the horizon, the folic-acid advice is the same with or without an MTHFR variant.”
EMR note: copy, paste and edit
MTHFR RESULT - REVIEW Source of result: [panel / DTC / functional-medicine / other] Reported MTHFR genotype: [C677T / A1298C / compound het / other] Question 1 - does the genotype change treatment? FDA psychotropic label naming MTHFR: [none] CPIC guideline: [none] DPWG (folic acid/MTX only): [n/a to psych] Decision: [no change on the genotype; not re-tested] Question 2 - biochemical state? Clinical reason to test: [Y/N] B12 / folate by indication (MMA for B12; homocysteine nonspecific): [ ] Action on measured result: [ ] Question 3 - folate as a treatment? L-methylfolate (not folic acid) considered on evidence, not genotype: [Y/N] Decision + reason: [ ] Discussed, commercial-neutral: [Y] Documented: [Y] Clinician: [ ] Date/time: [ ]
Case 1: a reported MTHFR variant — no change on the genotype
A patient on a working antidepressant brings a report flagging a homozygous or compound-heterozygous MTHFR variant and asks to add L-methylfolate or switch drugs “because of my MTHFR.”
Resolution
No FDA psychotropic label, CPIC guideline or DPWG action ties the MTHFR genotype to a drug change [11][12][13], and ACMG and RACGP find MTHFR testing does not change management in the contexts they address [1][21]. Read the result for context and make no change on the genotype. Because the germline result will not change, there is nothing to re-test. If a clinical reason exists, order serum B12 and/or folate by indication (MMA for an equivocal B12; homocysteine nonspecific) and act on the measurement. The folate-supplement request is a separate treatment decision, weighed on the L-methylfolate evidence (modest, weak/second-line) rather than on the genotype [2][4][5]. Stop relying on the genotype at the point you have either read it for context or obtained the biochemical measurement — it adds nothing beyond that.
Case 2: a measured biochemical abnormality — the real reason to act
A different patient has a clinical picture suggesting deficiency; testing shows a genuine folate or B12 deficiency, independent of any MTHFR genotype (an elevated homocysteine may or may not accompany it).
Resolution
Here a confirmed deficiency, not the genotype, is the reason to act. Evaluate and treat a confirmed folate or B12 deficiency on its own merits per general medical practice, keeping that decision separate from any MTHFR result. An isolated elevated homocysteine is nonspecific — it is multifactorial (renal, nutritional, medication and other causes) and does not by itself establish a vitamin deficiency or an indication to supplement; interpret it in context and direct treatment at the identified cause [1]. Recheck the measurement to confirm response — not the genotype, which does not change and did not drive the decision. A fasting homocysteine may be obtained in a thermolabile homozygote to inform counseling, but no held source provides a treatment threshold, so none is stated here [1].
Why it matters
MTHFR is one of the most frequently misread results in psychiatry: a common, modestly penetrant variant is treated as if it were a diagnosis or a prescribing instruction. Separating the genotype question from the treatment question — and naming the source for each, at its own scope — lets a prescriber give a clear, honest answer, avoid an unnecessary change or test, and still act on a real, measured abnormality when one is present.
References
- Hickey SE, Curry CJ, Toriello HV; Professional Practice and Guidelines Committee. ACMG Practice Guideline: lack of evidence for MTHFR polymorphism testing. Genet Med. 2013;15(2):153–156. doi:10.1038/gim.2012.165. Reaffirmed 27 April 2020 and reclassified a Clinical Practice Resource: Bashford MT, Hickey SE, Curry CJ, Toriello HV. Genet Med. 2020;22(12):2125. doi:10.1038/s41436-020-0843-0. (Scope: thrombophilia, recurrent pregnancy loss, at-risk relatives; not psychiatric use.)
- Papakostas GI, Shelton RC, Zajecka JM, et al. L-methylfolate as adjunctive therapy for SSRI-resistant major depression: results of two randomized, double-blind, parallel-sequential trials. Am J Psychiatry. 2012;169(12):1267–1274. doi:10.1176/appi.ajp.2012.11071114. (Abstract only held.)
- Sarris J, Murphy J, Mischoulon D, et al. Adjunctive nutraceuticals for depression: a systematic review and meta-analyses. Am J Psychiatry. 2016;173(6):575–587. doi:10.1176/appi.ajp.2016.15091228. (Abstract only held.)
- Maruf AA, Poweleit EA, Brown LC, Strawn JR, Bousman CA. Systematic review and meta-analysis of L-methylfolate augmentation in depressive disorders. Pharmacopsychiatry. 2022;55(3):139–147. doi:10.1055/a-1681-2047. (Abstract only held.)
- Lam RW, Kennedy SH, Adams C, et al. Canadian Network for Mood and Anxiety Treatments (CANMAT) 2023 update on clinical guidelines for management of major depressive disorder in adults. Can J Psychiatry. 2024;69(9):641–687. doi:10.1177/07067437241245384.
- Sarris J, Ravindran A, Yatham LN, et al. Clinician guidelines for the treatment of psychiatric disorders with nutraceuticals and phytoceuticals: WFSBP and CANMAT taskforce. World J Biol Psychiatry. 2022;23(6):424–455. doi:10.1080/15622975.2021.2013041. (Abstract only held.)
- Taylor MJ, Carney SM, Goodwin GM, Geddes JR. Folate for depressive disorders. Cochrane Database Syst Rev. 2003;(2):CD003390. doi:10.1002/14651858.CD003390. (Abstract + Cochrane summary held; folic acid or 5-methyltetrahydrofolate.)
- Bedson E, Bell D, Carr D, et al. Folate Augmentation of Treatment — Evaluation for Depression (FolATED): randomised trial and economic evaluation. Health Technol Assess. 2014;18(48). doi:10.3310/hta18480. (Folic acid 5 mg, not L-methylfolate; abstract held.)
- Mech AW, Farah A. Correlation of clinical response with homocysteine reduction during therapy with reduced B vitamins in patients with MDD who are positive for MTHFR C677T or A1298C polymorphism: a randomized, double-blind, placebo-controlled study. J Clin Psychiatry. 2016;77(5):668–671. doi:10.4088/JCP.15m10166. ClinicalTrials.gov NCT02709668 (“post hoc analysis”; no results posted). (Abstract + registry held; genotype-selected, no genotype-negative arm.)
- U.S. Food and Drug Administration. Guidance for Industry: Frequently Asked Questions About Medical Foods, Third Edition (March 2023). And 21 CFR 101.9(j)(8). (Medical foods are not drugs; no prescription requirement; no L-methylfolate/MTHFR text.)
- U.S. Food and Drug Administration. Table of Pharmacogenetic Associations (content current 09/10/2026; no MTHFR) and Table of Pharmacogenomic Biomarkers in Drug Labeling (content current 08/12/2026; MTHFR only in the betaine/homocystinuria row). An author-conducted review via openFDA (25 Oct 2026) of selected psychotropic, antiepileptic and antifolate drug labels identified no MTHFR labeling in the drugs examined.
- Clinical Pharmacogenetics Implementation Consortium (CPIC) public API and ClinPGx, queried 25 Oct 2026: 29 published guidelines, none for MTHFR; MTHFR present only as three provisional gene–drug pairs (carboplatin, l-methylfolate, methotrexate), none scored for a recommendation.
- van der Pol KH, Nijenhuis M, Soree B, et al. Dutch Pharmacogenetics Working Group (DPWG) guideline for the gene–drug interaction of ABCG2, HLA-B and allopurinol, and MTHFR, folic acid and methotrexate. Eur J Hum Genet. 2024;32(2):155–162. doi:10.1038/s41431-022-01180-0. With ClinPGx DPWG annotations. (MTHFR–folic acid: no action; MTHFR–methotrexate: not a gene–drug interaction; abstract + annotations held.)
- U.S. Food and Drug Administration. Safety Communication: the FDA warns against the use of many genetic tests with unapproved claims to predict patient response to specific medications (31 Oct 2018). (No MTHFR mention; general PGx-claim caution.)
- American Academy of Child and Adolescent Psychiatry. Clinical Use of Pharmacogenetic Tests in Prescribing Psychotropic Medications for Children and Adolescents (Policy Statement, approved by Council March 2020). (Advises avoiding PGx testing to select psychotropics in youth; does not name MTHFR.)
- Bousman CA, Mukerjee G, Men X, et al. Encountering pharmacogenetic test results in the psychiatric clinic. Can J Psychiatry. 2022;67(2):95–100. doi:10.1177/07067437211058847. (Lists MTHFR among panel genes lacking sufficient evidence or guidelines.)
- Zeier Z, Carpenter LL, Kalin NH, et al. Clinical implementation of pharmacogenetic decision support tools for antidepressant drug prescribing. Am J Psychiatry. 2018;175(9):873–886. (PMC6774046.) (Describes a commercial panel that deemed MTHFR “actionable”.)
- Centers for Disease Control and Prevention. MTHFR Gene Variant and Folic Acid Facts (page dated 16 July 2026).
- MedlinePlus Genetics (U.S. National Library of Medicine). MTHFR gene (last updated 1 October 2019).
- U.S. Preventive Services Task Force. Folic Acid Supplementation to Prevent Neural Tube Defects: Preventive Medication. Final Recommendation Statement, 1 August 2023 (Grade A). (Addresses folic acid, not L-methylfolate; MTHFR mentioned only as a research gap.)
- Royal Australian College of General Practitioners. Genomics in general practice: MTHFR gene testing (last revised 19 December 2023). (Non-US professional body; offered as a supplement to ACMG.)
- DailyMed / openFDA product labels for L-methylfolate medical foods (public records), cited only for status and the inconsistency of MTHFR wording across labels; no product is named or endorsed in this chapter.
Reviewed against held full-text sources through an OpenEvidence pass and two independent ChatGPT review rounds; all source citations verified. The highlighted conflict-of-interest disclosure is to be confirmed by Dr. Singh before publishing. Part of the Psychiatry Education Forum Academy, Genetic Testing in Psychiatry · Section D · Chapter 8.
Next: Chapter 9
Continuing Section D (What not to act on): SLC6A4, HTR2A and ANK3.
This chapter is educational material for licensed prescribers and prescribers in training. It is not a substitute for clinical judgment, local protocols, the current prescribing information, or the laboratory’s report. Psychiatry Education Forum Academy has no financial relationship with any pharmacogenomic or genetic testing company, nor with any maker of folate or L-methylfolate products. Psychiatry Education Forum Academy is not a CME provider and this chapter does not carry CME credit.
Responses