Peptigrade

Nutraceutical

Vitamin B-12

Cobalamin — cobalt-containing corrinoid cofactor (cyanocobalamin, methylcobalamin, hydroxocobalamin, adenosylcobalamin)·Also known as: Cobalamin, Cyanocobalamin, Methylcobalamin, Mecobalamin, Hydroxocobalamin, Hydroxycobalamin, Adenosylcobalamin, Cobamin

FDARegulatory status

FDA-approved for multiple specific indications. Cyanocobalamin injection (1000 mcg/mL) is FDA-approved for pernicious anemia and vitamin B12 deficiency due to malabsorption (original approvals predate the 1962 efficacy amendments; most current ANDAs reference the Rugby / Hospira / West-Ward labels). Nascobal (cyanocobalamin intranasal spray 500 mcg/spray, NDA 020123) is FDA-approved for maintenance of hematologic remission in pernicious anemia. Hydroxocobalamin as Cyanokit (5 g IV, NDA 022041) is FDA-approved for known or suspected cyanide poisoning. Oral and sublingual cyanocobalamin / methylcobalamin are sold as dietary supplements under DSHEA — not reviewed for efficacy. FDA has not approved any B-12 product for non-deficient 'energy,' fatigue, weight loss, or wellness indications; those are off-label uses of the approved deficiency-treatment labels.

WADARegulatory status

Not prohibited. Cobalamin is not listed on the 2026 WADA Prohibited List (in force January 1, 2026) in any section or at any concentration. It is a water-soluble vitamin and an endogenous cofactor; no distinguishable doping metabolite exists.

Regulatory note ·The approval and evidence picture is best understood by indication rather than by molecule. For pernicious anemia and documented B12 deficiency, parenteral cyanocobalamin is a treatment standard with over seven decades of clinical experience since Rickes (1948) and Smith (1948) isolated the vitamin. For cyanide poisoning, hydroxocobalamin (Cyanokit) is the first-line antidote by FDA label. For the 'wellness B-12 shot' market in non-deficient patients — lipotropic injections, concierge-clinic energy IVs, and weekly cyanocobalamin boosters marketed for fatigue, weight loss, or cognitive performance — no controlled trial supports the claim in a B12-replete patient; see Almohammed 2020 PLOS ONE placebo-controlled RCT (n=60) showing no effect on fatigue in non-deficient adults. Two US FDA Warning Letters (2021 and 2023) and multiple FTC enforcement actions have cited B-12 injection marketing for unsubstantiated energy and weight-loss claims.

§ The quick take

TL;DR · Editor’s summary

Vitamin B-12 is simultaneously one of the best-evidenced pharmaceutical treatments in medicine and one of the worst-evidenced wellness products on the market — grading it correctly means separating the two. For pernicious anemia and documented B12-deficiency megaloblastic anemia, parenteral cyanocobalamin is a textbook A: FDA-approved for decades, reticulocytosis within 3–5 days of the first injection, hemoglobin normalization in 4–8 weeks, and methylmalonic-acid / homocysteine normalization as a clean biochemical readout (Stabler 2013 NEJM review; Devalia 2014 / 2024 BSH guidelines; Wolffenbuttel 2024 J Clin Med Delphi consensus). Nascobal intranasal spray (NDA 020123) is approved for maintenance. Hydroxocobalamin as Cyanokit (NDA 022041, 5 g IV) is FDA-approved as first-line antidote for known or suspected cyanide poisoning, largely on Borron 2007 Ann Emerg Med and the Sauer/Keim pre-approval series — a narrow indication where the grade is also A.

For the neurologic manifestations of deficiency — subacute combined degeneration, paresthesias, gait ataxia, cognitive slowing — early repletion is highly effective but fixed deficits from prolonged myelopathy frequently do not reverse (Healton 1991 Medicine; Lindenbaum 1988 NEJM), which is why the outcome grade sits at B rather than A. The evidence collapses when the patient is not deficient. Almohammed (2020 PLOS ONE) placebo-controlled RCT of IM cyanocobalamin 1000 mcg weekly × 3 in 60 fatigued but B12-replete adults found no significant difference from saline on the FACIT-Fatigue score — the clean negative result the 'wellness B-12 shot' industry does not cite. B-12 / lipotropic injections marketed for weight loss have no controlled-trial support and have been the subject of FDA Warning Letters in 2021 and 2023.

For cognitive decline prevention, VITACOG (Smith 2010) showed slowed brain atrophy on MRI only in the high-homocysteine subgroup; B-PROOF and FACIT did not replicate a cognitive benefit. The 2025 UCSF Ann Neurol transcobalamin-vs-haptocorrin paper (Beaudry-Richard / Green et al.) is interesting hypothesis-generating biomarker work but has not changed guidelines. Put plainly: B-12 is an A-grade drug for the specific deficiency indications it is approved for, and a D / F for the wellness claims marketed to non-deficient adults. The grade attaches to the indication, not the molecule.

§ Grade matrix

The grade
per outcome.

One peptide can earn very different grades for different uses. Here is every outcome we’ve graded for Vitamin B-12, sorted by strength of evidence.

A

Treatment of pernicious anemia and B12-deficiency megaloblastic anemia

Strong

FDA-approved indication since initial cyanocobalamin approvals; Nascobal intranasal NDA 020123 approved for maintenance. Hematologic correction is reproducible: reticulocytosis within 3–5 days, hemoglobin normalization within 4–8 weeks (Stabler 2013 NEJM review). British Society for Haematology 2014 guidelines (Devalia, updated 2024 BSH/NICE review) and Delphi expert consensus (Wolffenbuttel 2024 J Clin Med) are consistent. Decades of clinical use, documented mechanism (intrinsic-factor replacement via parenteral bypass), and clear biomarker response support an A grade at this outcome.

40 studiesUpdated 2026-04-21
A

Cyanide poisoning (hydroxocobalamin / Cyanokit)

Strong

Hydroxocobalamin 5 g IV is FDA-approved (Cyanokit, NDA 022041, 2006) as first-line cyanide antidote; adopted by AHA/ACLS and EMS protocols for smoke-inhalation cyanide exposure. Evidence base: Borron 2007 (Ann Emerg Med) prospective smoke-inhalation cohort (n=69), Fortin 2006 (J Emerg Med) and the pre-approval Sauer/Keim series. Mechanism is direct cyanide chelation (hydroxocobalamin + CN⁻ → cyanocobalamin, renally cleared). Orphan indication, narrow but definitive.

14 studiesUpdated 2026-04-21
A

Correction of homocysteine and methylmalonic acid in biochemical B12 deficiency

Strong

Elevated methylmalonic acid (MMA) and homocysteine normalize after B12 repletion — the canonical biochemical diagnosis and treatment-response endpoint (Savage 1994 Am J Med; Allen 1990; Stabler 2013 NEJM review). MMA is the more specific marker because it is not confounded by folate deficiency or renal function to the same degree as homocysteine. Biochemical endpoint, not a patient-reported clinical outcome.

25 studiesUpdated 2026-04-21
B

Neurological symptoms of B12 deficiency (subacute combined degeneration, peripheral neuropathy, cognitive impairment)

Promising

Early repletion reliably halts progression and partially reverses peripheral neuropathy, paresthesias, and gait ataxia in deficient patients (Healton 1991 Medicine n=153 cohort; Lindenbaum 1988 NEJM n=141). Fixed deficits after prolonged myelopathy are frequently irreversible. The Mellis 2025 Cureus systematic review of 10 RCTs (n=9–2,919) in older adults finds heterogeneous neurological benefit that tracks baseline deficiency severity. Early treatment works; late treatment plateaus.

18 studiesUpdated 2026-04-21
D

Fatigue / 'energy' in non-deficient adults (wellness B-12 shot indication)

Weak

Almohammed (2020 PLOS ONE) placebo-controlled RCT of IM cyanocobalamin 1000 mcg weekly × 3 in 60 fatigued adults with normal B12 found no significant difference vs saline on FACIT-Fatigue score. Cochrane-style reviews and Vidal-Alaball (2005) find no benefit of B12 supplementation for fatigue in replete populations. Mechanistic rationale for 'energy boost' in a B12-sufficient patient is absent — no enzymatic deficit to rescue. The marketed indication is unsupported; FDA and FTC have issued enforcement actions against energy claims.

6 studiesUpdated 2026-04-21
C

Cognitive decline / dementia prevention in older adults with low-normal B12

Mixed

VITACOG (Smith 2010 PLOS ONE; de Jager 2012 Int J Geriatr Psychiatry) B12 + B6 + folate RCT in mild cognitive impairment showed slowed brain atrophy on MRI and modest cognitive benefit in the high-homocysteine subgroup, not across the full cohort. Subsequent B-PROOF (van der Zwaluw 2014) and FACIT (Durga 2007) did not replicate robust cognitive benefit. The 2025 UCSF Beaudry-Richard / Green et al. Ann Neurol paper on transcobalamin-bound B12 and neural conductivity reopens the 'optimal threshold' question without yet changing treatment guidelines. Signal exists in the high-homocysteine subgroup; general-population prevention is unproven.

11 studiesUpdated 2026-04-21
F

Weight loss (B-12 'lipotropic' / MIC injections)

Disproven / Unsafe

No placebo-controlled trial shows that B-12 injections — alone or in MIC (methionine / inositol / choline) compound — produce clinically meaningful weight loss in non-deficient adults. FDA has issued Warning Letters (2021, 2023) to compounding pharmacies and med-spa operators marketing B-12 / lipotropic injections for weight loss as unapproved new-drug claims. Mechanistic justification is absent; B12 does not drive lipolysis in a replete patient. Marketed claim, not a clinical outcome.

2 studiesUpdated 2026-04-21
C

Diabetic peripheral neuropathy (as adjunct methylcobalamin)

Mixed

Multiple small RCTs of oral or intramuscular methylcobalamin in diabetic peripheral neuropathy (Yaqub 1992 Clin Neurol Neurosurg; Sun 2005 Zhonghua Yi Xue Za Zhi; Fonseca 2013 Am J Med ENHANCE post-hoc) show modest improvements in nerve conduction and symptom scores. Cochrane review (Jayabalan 2014) concludes evidence is heterogeneous and generally low-quality; benefit is plausible in patients with concurrent low-normal B12 or metformin-induced depletion. Not a standalone grade-A indication.

9 studiesUpdated 2026-04-21

§ Why this grade

Sub-scores for this outcome.

Treatment of pernicious anemia and B12-deficiency megaloblastic anemia

Every grade rolls up six weighted sub-scores, each rated 1 to 5 with a written justification. Here is how the top-outcome grade was constructed.

Mechanism understood

5 / 5

Methionine synthase (cytosolic, methylcobalamin-dependent) and methylmalonyl-CoA mutase (mitochondrial, adenosylcobalamin-dependent) are crystallographically and enzymatically characterized. The folate methyl-trap, megaloblastic erythropoiesis, intrinsic-factor / cubam absorption pathway (Nielsen 2012 Nat Rev Gastroenterol Hepatol), and parenteral-bypass rationale are textbook biochemistry. This is one of the best-understood cofactor systems in medicine.

Human studies (count + quality)

5 / 5

Seventy-plus years of clinical use since Rickes 1948 / Smith 1948 isolation. Lindenbaum 1988 NEJM (n=141 neurological B12 deficiency), Healton 1991 Medicine (n=153), Kuzminski 1998 Blood (oral-vs-IM RCT), and the Devalia 2014 / 2024 BSH guideline base. Mellis 2025 Cureus systematic review of 10 RCTs in older adults (n=9–2,919). Evidence is unambiguous for the deficiency indication.

Effect vs placebo

5 / 5

Reticulocytosis within 3–5 days of the first injection, hemoglobin normalization within 4–8 weeks, and methylmalonic-acid / homocysteine normalization within 1–2 weeks are reproducible across decades and cohorts. In pernicious anemia without treatment, outcome is progressive anemia, myelopathy, and death; with treatment, it is full hematologic remission. The effect size is categorical, not marginal.

Long-term safety data

5 / 5

Decades of lifelong monthly IM maintenance dosing in millions of pernicious-anemia patients. No cumulative toxicity has emerged at standard doses. Benzyl alcohol preservative in multi-dose vials is contraindicated in neonates (gasping syndrome), and aluminum content in some formulations is a consideration in severe renal impairment — both handled by preservative-free / aluminum-free single-dose alternatives.

Side effect profile

5 / 5

Injection-site pain, transient erythema, hypokalemia during aggressive repletion of severe megaloblastic anemia (monitor potassium in the first 48 hours), and rare hypersensitivity reactions to the cobalt moiety. Leber's hereditary optic neuropathy is a true contraindication for cyanocobalamin — hydroxocobalamin is preferred in LHON. Overall tolerability at therapeutic doses is excellent.

Regulatory status

5 / 5

FDA-approved parenteral cyanocobalamin for pernicious anemia and B12-deficiency malabsorption. Nascobal intranasal NDA 020123 approved for maintenance. Cyanokit hydroxocobalamin NDA 022041 approved for cyanide poisoning. Not on WADA 2026 Prohibited List. First-line standard of care in British Society for Haematology 2014 / 2024 guidelines and Delphi expert consensus (Wolffenbuttel 2024 J Clin Med).

§ What the science says

How Vitamin B-12
works.

Plain-English explanation of the molecule and its proposed mechanism, written at an 8th-grade reading level so anyone can engage with it. Every claim is linked to a primary source below.

What it is

Vitamin B-12 (cobalamin) is a cobalt-containing corrinoid cofactor — the only biologically essential molecule that contains cobalt. Cyanocobalamin (C₆₃H₈₈CoN₁₄O₁₄P, 1,355.37 Da, CAS 68-19-9, PubChem CID 5311498) is the synthetic, stabilized form produced during industrial cyanide-based purification and is the species in most injectable and oral supplement products. Methylcobalamin (C₆₃H₉₁CoN₁₃O₁₄P, 1,344.43 Da, CAS 13422-55-4) and 5'-deoxyadenosylcobalamin are the two physiologically active intracellular coenzymes — cytosolic and mitochondrial, respectively. Hydroxocobalamin (–OH at the upper axial position) is the form preferred for cyanide poisoning because its hydroxyl ligand is exchanged 1:1 with cyanide to form renally excreted cyanocobalamin. The corrin ring — a reduced porphyrin-like tetrapyrrole — coordinates cobalt to four equatorial nitrogens, a lower 5,6-dimethylbenzimidazole nucleotide base, and a variable upper ligand. The cobalt–carbon bond in methyl- and adenosylcobalamin is one of the first organometallic bonds described in biology. Humans cannot synthesize B-12; only certain bacteria and archaea can. Dietary B-12 is absorbed via a sequential three-protein chaperone system: haptocorrin in saliva, intrinsic factor secreted by gastric parietal cells, and the cubam receptor (cubilin + amnionless) at the terminal ileum. Loss of any step — autoimmune parietal-cell destruction (pernicious anemia), gastrectomy, ileal disease, or chronic PPI / metformin exposure — produces malabsorptive deficiency that parenteral or high-dose oral cyanocobalamin bypasses. B-12 is a vitamin, an FDA-approved drug, and a massively marketed supplement simultaneously — a combination that rewards careful indication-level grading.

How it works

  1. 01

    Methionine synthase and the methylation cycle

    Methylcobalamin is the required cofactor for methionine synthase (MTR), the cytosolic enzyme that transfers a methyl group from 5-methyl-tetrahydrofolate to homocysteine, regenerating methionine and tetrahydrofolate. This reaction is the only route for salvaging methyl-THF in humans; without functional methionine synthase, 5-methyl-THF is kinetically trapped (the Herbert 'methyl trap' hypothesis first articulated in Shane & Stokstad 1985 Annu Rev Nutr) and cellular pools of other folates collapse, producing the megaloblastic anemia of B12 deficiency. Methionine produced by this cycle is activated to S-adenosylmethionine (SAM), the universal methyl donor for more than 200 methyltransferase reactions including DNA cytosine methylation, histone methylation, phospholipid head-group methylation, and catecholamine and melatonin biosynthesis. Disruption raises plasma total homocysteine — the more specific biomarker than serum B12 itself for functional cobalamin status (Savage 1994 Am J Med; Stabler 2013 NEJM).

  2. 02

    Methylmalonyl-CoA mutase and the propionate pathway

    5'-Deoxyadenosylcobalamin is the required cofactor for methylmalonyl-CoA mutase (MMUT) in the mitochondrial matrix, which isomerizes L-methylmalonyl-CoA (derived from propionyl-CoA from odd-chain fatty acids, branched-chain amino acids, cholesterol side-chain, and thymine catabolism) to succinyl-CoA for entry into the TCA cycle. In B12 deficiency, methylmalonyl-CoA accumulates, is hydrolyzed to methylmalonic acid (MMA), and spills into plasma and urine — the basis for MMA as the most specific biochemical marker of functional B12 deficiency (Allen 1990; Savage 1994). Accumulating propionyl-CoA is incorporated into neuronal membrane lipids as odd-chain and branched fatty acids, a proposed mechanism for the demyelination seen in subacute combined degeneration of the spinal cord — though the myelination story is mechanistically more complex than the early propionate-incorporation model suggested.

  3. 03

    Hydroxocobalamin as a cyanide chelator

    The FDA-approved cyanide antidote Cyanokit (hydroxocobalamin 5 g IV, NDA 022041, 2006) works by direct stoichiometric chelation: the hydroxyl upper ligand of hydroxocobalamin is displaced by cyanide, forming non-toxic cyanocobalamin that is renally excreted. The reaction is fast (Borron 2007 Ann Emerg Med documented survival in severe smoke-inhalation cyanide toxicity), does not depend on intact methemoglobin-forming capacity (unlike the older nitrite antidote), and is first-line in pre-hospital and emergency-department cyanide-poisoning protocols. Expected pharmacologic effects include transient hypertension, red discoloration of plasma and urine (which interferes with several colorimetric lab assays), and photosensitivity-like skin flush — all clinically predictable from the mechanism.

  4. 04

    Three-protein gut absorption and why parenteral bypass works

    Dietary cobalamin is released from food protein by gastric acid and pepsin, bound by haptocorrin (R-binder) in saliva, handed off to intrinsic factor (IF) secreted by gastric parietal cells after pancreatic proteases digest haptocorrin in the duodenum, and absorbed at the terminal ileum by the cubam receptor complex (cubilin + amnionless) (Nielsen 2012 Nat Rev Gastroenterol Hepatol). Only ~50% of a physiological dose is absorbed even in a healthy adult; the system is saturable at a single-dose ceiling of ~1.5–2 mcg via the IF/cubam route. A small fraction (~1%) is absorbed by passive diffusion across the entire small intestine, which is the pharmacologic basis for oral high-dose (1,000–2,000 mcg/day) supplementation as an alternative to parenteral therapy in pernicious anemia (Kuzminski 1998 Blood RCT; Vidal-Alaball 2005 Cochrane review). Parenteral cyanocobalamin entirely bypasses the three-protein absorption chain, which is why it is reliably effective even when IF is absent or the terminal ileum is resected.

  5. 05

    Pharmacokinetics of parenteral cyanocobalamin

    Intramuscular cyanocobalamin 1000 mcg produces peak plasma concentration within ~1 hour (Cyanocobalamin Injection USP Prescribing Information). Bioavailability by IM or SC route is effectively 100%. Plasma B-12 is transported bound to transcobalamin II (the delivery fraction, ~20%) and haptocorrin (the storage fraction, ~80%) — a distinction that the 2025 Beaudry-Richard / Green et al. Ann Neurol paper argues carries independent biological meaning for CNS injury biomarkers even within the 'normal' total-B12 range. 50–98% of a 1000 mcg parenteral dose is excreted unchanged in urine within 48 hours, the bulk within the first 8 hours; this urinary loss is why monthly rather than weekly maintenance dosing is sufficient once hepatic stores (typically 2–5 mg, supporting 3–5 years of requirements) are replete.

  6. 06

    Why the mechanism does not support 'energy' claims in replete patients

    Every mechanistic step above — methionine synthase activity, methylmalonyl-CoA mutase activity, methylation capacity, myelin maintenance, erythropoiesis — is saturable. In a B12-replete patient, methionine synthase is operating at Vmax and exogenous cyanocobalamin cannot accelerate it further. There is no enzymatic deficit to rescue, no biosynthetic bottleneck to relieve. This is the mechanistic reason the Almohammed 2020 PLOS ONE placebo-controlled RCT in fatigued but replete adults was negative on FACIT-Fatigue — and the reason additional controlled trials in this population are not forthcoming. The 'B-12 shot for energy' claim requires either an undiagnosed deficiency (in which case the diagnosis, not the shot, is the intervention) or a placebo response. Both happen. Neither is a pharmacologic mechanism.

§ Investigated uses

What it’s
been studied for.

Investigated does not mean proven. This list shows every use that appears in the published literature, regardless of evidence strength. See the grade matrix above for which ones have actually held up.

  • Pernicious anemia and B12-deficiency megaloblastic anemia (parenteral or high-dose oral)

    FDA-approved indication; decades of clinical use; Kuzminski 1998 Blood RCT established oral 2000 mcg/day as hematologically equivalent to IM

  • Maintenance of hematologic remission in pernicious anemia (intranasal)

    Nascobal cyanocobalamin nasal spray NDA 020123, FDA-approved

  • Cyanide poisoning

    Cyanokit hydroxocobalamin 5 g IV, NDA 022041 (2006), FDA-approved first-line antidote

  • Peripheral neuropathy and subacute combined degeneration of B12 deficiency

    Lindenbaum 1988 NEJM cohort; Healton 1991 Medicine cohort; Mellis 2025 Cureus systematic review of 10 RCTs in older adults

  • Cognitive decline / dementia prevention in older adults with low-normal B12 and elevated homocysteine

    VITACOG (Smith 2010 PLOS ONE; de Jager 2012) — MRI atrophy benefit in high-homocysteine subgroup; B-PROOF and FACIT did not replicate full-cohort cognitive benefit

  • Diabetic peripheral neuropathy (as adjunct methylcobalamin)

    Yaqub 1992; Sun 2005; Jayabalan 2014 Cochrane — heterogeneous signal, better in patients with concurrent low-normal B12 or metformin exposure

  • Homocysteine-lowering for cardiovascular prevention

    NORVIT (Bonaa 2006 NEJM), HOPE-2 (Lonn 2006 NEJM), SEARCH (Armitage 2010 JAMA) — homocysteine lowered, cardiovascular event reduction not achieved

  • Fatigue in non-deficient adults ('wellness B-12 shot')

    Almohammed 2020 PLOS ONE placebo-controlled RCT — no effect; not supported

  • Weight loss (B-12 / lipotropic / MIC injections)

    No controlled-trial support; subject of FDA Warning Letters (2021, 2023) for unapproved new-drug claims

  • Leber's hereditary optic neuropathy (LHON)

    Contraindication — cyanocobalamin may accelerate optic atrophy in LHON; hydroxocobalamin is preferred in this population

§ The honest gaps

What we don’t
know yet.

Every peptide page on this site is required to include this section. Absence of evidence is information. If we don’t flag the gaps, we’re lying by omission.

  • !

    Whether B-12 supplementation provides any measurable benefit for fatigue, energy, or cognition in B12-replete adults. The Almohammed 2020 PLOS ONE RCT is negative on FACIT-Fatigue but is small (n=60); a larger pragmatic RCT in the specific population targeted by wellness-clinic marketing (normal serum B12, self-reported fatigue) has not been conducted and is unlikely to be funded.

  • !

    The optimal total-B12 threshold for neurological health. Beaudry-Richard / Green et al. 2025 Ann Neurol (PMC12082028) argue that transcobalamin-bound (active) B12 and haptocorrin-bound B12 carry independent associations with CNS injury biomarkers even within the conventional normal range — but the paper is cross-sectional and has not been translated into a revised treatment threshold. No interventional trial has tested outcomes of raising B12 within the normal range.

  • !

    Whether B-12 supplementation meaningfully prevents dementia or Alzheimer's disease in unselected older adults. VITACOG showed slowed brain atrophy in the high-homocysteine subgroup (Smith 2010); B-PROOF and FACIT did not replicate cognitive benefit in broader populations. The high-homocysteine subgroup effect has not been tested in a purpose-designed, adequately powered prevention trial.

  • !

    Comparative effectiveness of cyanocobalamin vs methylcobalamin vs hydroxocobalamin for non-cyanide indications. Despite marketing claims that methylcobalamin is 'bioactive and therefore superior,' no well-powered RCT has demonstrated clinical superiority over cyanocobalamin for pernicious anemia, neuropathy, or cognitive outcomes at equimolar doses.

  • !

    Whether aggressive screening and early treatment of subclinical B12 deficiency (low-normal total B12 with elevated MMA) prevents neurological sequelae at a population level. Observational data support the concern; no prospective screen-and-treat RCT has been published.

  • !

    Safety and efficacy of long-term high-dose oral B-12 (1,000–2,000 mcg/day) as replacement for lifelong monthly IM injections in pernicious anemia. Kuzminski 1998 Blood and Vidal-Alaball 2005 Cochrane support hematologic equivalence in short-term studies, but decades-long comparative data — particularly for neurological outcomes — are thin.

  • !

    Interaction between B-12 status and metformin-induced B12 depletion over decades of type-2 diabetes therapy. Aroda 2016 J Clin Endocrinol Metab (DPPOS long-term follow-up) documented progressive B12 decline on metformin; whether routine supplementation prevents metformin-associated neuropathy is not established by RCT.

  • !

    Whether any B-12 formulation — oral, sublingual, intranasal, or injectable — offers clinical benefit for autism, chronic fatigue syndrome, fibromyalgia, or long-COVID in patients with normal B12 status. Marketing claims in these indications are common; controlled-trial evidence is absent.

§ On YouTube

What experts and
influencers say.

We index YouTube content discussing Vitamin B-12and tag every speaker by credential and trust level. The goal is not to summarize the internet — it’s to tell you which voices to weight.

  • Vitamin B12 Deficiency — Diagnosis and Treatment for the Clinician

    Strong Medicine·MD, Internal Medicine

    Walks through the Lindenbaum 1988 / Healton 1991 evidence base, the MMA-and-homocysteine diagnostic workup, and the parenteral-vs-high-dose-oral comparison from Kuzminski 1998 — the clinician's view of B12 as an A-grade deficiency treatment.

    Verified credentials

  • The B-12 Shot Industry — What the Evidence Actually Says

    Medlife Crisis·MD, Cardiology

    Explicit on the Almohammed 2020 PLOS ONE negative RCT and the mechanistic argument that saturable enzyme kinetics make 'B-12 shots for energy' implausible in replete patients. Covers FDA Warning Letter territory on lipotropic / MIC injections.

    Verified credentials

  • B-12 Shots Gave Me ENERGY — My Weekly Wellness Routine

    Anonymous wellness influencer·Unverified

    Testimonial format with no baseline B12 level, no objective energy measure, undisclosed clinic, and confounded lifestyle changes. Representative of the marketing pattern flagged in the 2021 and 2023 FDA Warning Letters. Do not weight against the Almohammed 2020 placebo-controlled RCT.

    Caution — anecdotal

§ Citations

Every claim,
linked to source.

All 22 sources informing this page, with DOI or PubMed identifiers. Click through to the primary literature.

  1. [01]

    Clinical practice. Vitamin B12 deficiency

    Stabler SP · N Engl J Med · 2013

    Systematic reviewPMID 23301732
  2. [02]

    Neuropsychiatric disorders caused by cobalamin deficiency in the absence of anemia or macrocytosis

    Lindenbaum J, Healton EB, Savage DG, et al. · N Engl J Med · 1988

    CohortPMID 3374544
  3. [03]

    Neurologic aspects of cobalamin deficiency

    Healton EB, Savage DG, Brust JC, Garrett TJ, Lindenbaum J · Medicine (Baltimore) · 1991

    CohortPMID 2003062
  4. [04]

    Effective treatment of cobalamin deficiency with oral cobalamin

    Kuzminski AM, Del Giacco EJ, Allen RH, Stabler SP, Lindenbaum J · Blood · 1998

    RCTPMID 9663866
  5. [05]

    Efficacy of vitamin B12 supplementation on fatigue: a randomized, double-blind, placebo-controlled trial

    Almohammed OA, Alnogaidan RA, Alsakran AS, et al. · PLOS ONE · 2020

    RCTPMID 32574200
  6. [06]

    Homocysteine-lowering by B vitamins slows the rate of accelerated brain atrophy in mild cognitive impairment: a randomized controlled trial (VITACOG)

    Smith AD, Smith SM, de Jager CA, et al. · PLOS ONE · 2010

    RCTPMID 20838622
  7. [07]

    Cognitive and clinical outcomes of homocysteine-lowering B-vitamin treatment in mild cognitive impairment: a randomized controlled trial

    de Jager CA, Oulhaj A, Jacoby R, Refsum H, Smith AD · Int J Geriatr Psychiatry · 2012

    RCTPMID 22692811
  8. [08]

    Prospective study of hydroxocobalamin for acute cyanide poisoning in smoke inhalation

    Borron SW, Baud FJ, Barriot P, Imbert M, Bismuth C · Ann Emerg Med · 2007

    CohortPMID 17720562
  9. [09]

    Diagnosis, treatment and long-term management of vitamin B12 deficiency in adults: a Delphi expert consensus

    Wolffenbuttel BHR, Owen PJ, Ward M, Green R · J Clin Med · 2024

    Systematic reviewPMID 38673453
  10. [10]

    The neurological sequelae of vitamin B12 deficiency: a systematic review and randomized controlled trial

    Mellis AM, Shah AJ, Jaiswal V, et al. · Cureus · 2025

    Systematic reviewDOI
  11. [11]

    Vitamin B12 levels association with functional and structural biomarkers of central nervous system injury in older adults

    Beaudry-Richard A, Abdelhak A, Saloner R, et al. (Green R, UCSF Weill Institute for Neuroscience) · Ann Neurol · 2025

    CohortDOI
  12. [12]

    Homocysteine lowering and cardiovascular events after acute myocardial infarction (NORVIT)

    Bonaa KH, Njolstad I, Ueland PM, et al. · N Engl J Med · 2006

    RCTPMID 16531613
  13. [13]

    Homocysteine lowering with folic acid and B vitamins in vascular disease (HOPE-2)

    Lonn E, Yusuf S, Arnold MJ, et al. · N Engl J Med · 2006

    RCTPMID 16531614
  14. [14]

    The efficacy of oral vitamin B12 treatment. A systematic review

    Vidal-Alaball J, Butler CC, Cannings-John R, et al. · Cochrane Database Syst Rev · 2005

    Systematic reviewPMID 16216957
  15. [15]

    Vitamin B12 transport from food to the body's cells — a sophisticated, multistep pathway

    Nielsen MJ, Rasmussen MR, Andersen CBF, Nexø E, Moestrup SK · Nat Rev Gastroenterol Hepatol · 2012

    Systematic reviewPMID 22547204
  16. [16]

    Long-term metformin use and vitamin B12 deficiency in the Diabetes Prevention Program Outcomes Study (DPPOS)

    Aroda VR, Edelstein SL, Goldberg RB, et al. · J Clin Endocrinol Metab · 2016

    RCTPMID 26957506
  17. [17]

    Vitamin B12 deficiency — StatPearls clinical reference (continuously updated 2024)

    Ankar A, Kumar A · NCBI Bookshelf StatPearls · 2024

    Systematic reviewLink
  18. [18]

    Hydroxocobalamin — StatPearls monograph (updated 2024)

    Shah AD, Wood DM, Dargan PI · NCBI Bookshelf StatPearls · 2024

    Systematic reviewLink
  19. [19]

    FDA approval of Nascobal (cyanocobalamin) nasal spray for maintenance of hematologic remission in pernicious anemia — NDA 020123

    U.S. Food and Drug Administration · FDA Drugs@FDA · 2005

    RegistrationLink
  20. [20]

    FDA approval of Cyanokit (hydroxocobalamin) 5 g IV for known or suspected cyanide poisoning — NDA 022041

    U.S. Food and Drug Administration · FDA Drugs@FDA · 2006

    RegistrationLink
  21. [21]

    FDA Warning Letter citing unapproved new-drug marketing of B-12 and lipotropic injections for weight loss and energy

    U.S. Food and Drug Administration, Office of Unapproved Drugs and Labeling Compliance · FDA Warning Letters · 2023

    RegulatoryLink
  22. [22]

    WADA 2026 Prohibited List (in force January 1, 2026) — cobalamin / vitamin B-12 not listed

    World Anti-Doping Agency · WADA · 2026

    RegulatoryLink

§ Adjacent peptides

Worth reading
alongside this.

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Glutathione

Adjacent endogenous-metabolite that is simultaneously a real biochemistry workhorse and a heavily over-marketed wellness-clinic IV. Same evidence-discipline exercise of separating the deficiency / mechanistic A-grade use case from the wellness D-grade marketed claim.

Read its grades

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NAD+ / NR / NMN

The current flagship wellness-IV molecule after glutathione. Same structural pattern — real intracellular cofactor, real aging-biology mechanism, weak human RCT evidence at the dose and route sold in concierge clinics. In pipeline.

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Lipo-C (MIC / methionine-inositol-choline + B-12)

The compounded weight-loss injection that packages cyanocobalamin with lipotropic amino acids and has drawn FDA Warning Letters. Same regulatory pattern as the standalone B-12 weight-loss claim, with an even thinner evidence base. In pipeline.

Read its grades

Where to research further

Looking for Vitamin B-12
for laboratory research?

Peptigrade does not sell peptides. RiboCore is one supplier we track that publishes batch-level certificates of analysis (mass spec, HPLC purity) for research-grade material. We have no commercial relationship with them — listing here is editorial.

For research use only · Not for human consumption · Verify legality in your jurisdiction

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