# Vitamin B12 (Methylcobalamin)

> Methylcobalamin (INN mecobalamin) is one of the two coenzyme forms of vitamin B12: a cobalt(III) corrinoid with a methyl group bonded directly to cobalt. Its formula is C63H91CoN13O14P (1344.4 g/mol). It serves as the cofactor for B12-dependent methyltransferases such as methionine synthase and has been studied in randomized trials in peripheral neuropathy and ALS.

Canonical: https://peptideproperties.com/compounds/methylcobalamin/

## Identity

- **Class:** Vitamins, Cofactors & Amino-Acid Derivatives
- **Molecular formula:** C63H91CoN13O14P
- **Molecular weight:** 1344.4 g/mol
- **Monoisotopic mass:** 1343.5878 Da
- **CAS number:** 13422-55-4
- **PubChem CID:** 10898559
- **InChIKey:** ZFLASALABLFSNM-WYVZQNDMSA-L

## Key facts

- Class: organometallic cobalt corrinoid; a coenzyme form of vitamin B12; INN mecobalamin
- Structure: methyl group bonded to cobalt(III) as the upper axial ligand of the corrin ring
- Formula C63H91CoN13O14P; molecular weight 1344.4 g/mol; CAS 13422-55-4
- Cofactor for B12-dependent methyltransferases, including methionine synthase
- Light-sensitive: the cobalt-carbon bond is cleaved by light
- Studied in randomized trials in diabetic neuropathy, ALS and chemotherapy-induced hand-foot syndrome
- Regulatory status: not an FDA-approved drug in the US; mecobalamin is a prescription drug in Japan

## What Is Methylcobalamin?

Methylcobalamin is one of the two coenzyme forms of vitamin B12, the other being adenosylcobalamin. Cobalamin from food becomes bioavailable through release from dietary protein, intrinsic factor-mediated absorption, transport by haptocorrin or transcobalamin, cellular uptake, and enzymatic conversion into these two cofactor forms[1].Methylcobalamin, also known by the INN mecobalamin, acts as a cofactor for B12-dependent methyltransferases[2]. It is also one of four vitamin B12 forms used commercially, alongside cyanocobalamin, hydroxocobalamin and 5'-deoxyadenosylcobalamin[3].Since its discovery, mecobalamin has been applied mainly to hyperhomocysteinemia and peripheral neuropathy[2]. More recent research includes randomized trials in amyotrophic lateral sclerosis (ALS) and in chemotherapy-associated hand-foot syndrome[4][5].

## Chemical Structure and Molecular Identity

Methylcobalamin is a cobalt(III) corrinoid in which a methyl group is bonded directly to the cobalt atom, making it a naturally occurring organometallic compound. PubChem (CID 10898559) lists the molecular formula C63H91CoN13O14P and a molecular weight of 1344.4 g/mol. The CAS number is 13422-55-4.The core is the same as in every cobalamin: a corrin macrocycle coordinating cobalt through four nitrogen atoms, with a 5,6-dimethylbenzimidazole nucleotide as the lower axial ligand. The forms differ only in the upper ligand. Methylcobalamin carries a methyl group where cyanocobalamin carries cyanide[3].
### Stability and analytical identification
The cobalt-carbon bond is the molecule's weak point. Light cleaves it, and in the presence of oxygen methylcobalamin is converted to hydroxocobalamin. A 2022 review compared the reactivity of the four commercial B12 forms under temperature, pH and light, and in the presence of oxidants, reductants and other water-soluble vitamins, and evaluated stabilization approaches[3].For identity and purity, laboratories typically use reversed-phase HPLC with visible-UV detection, often confirmed by mass spectrometry, and handle samples under light protection. Hydroxocobalamin and cyanocobalamin are the main related substances to separate and quantify.

## Research History and Development

Methylcobalamin research moved from cofactor biochemistry to clinical studies in homocysteine disorders and neuropathy, and later to randomized trials in ALS. A 2008 review covered its mechanism, pharmacokinetics and metabolism, and its clinical use as monotherapy or combined therapy in hyperhomocysteinemia and peripheral neuropathy[2].A 1998 monograph argued that methylcobalamin had a theoretical advantage over cyanocobalamin and some metabolic applications not shared by other B12 forms, and listed proposed areas of interest ranging from diabetic neuropathy to sleep disorders[6]. Such claims were largely untested by large controlled trials at the time.In ALS, a long-term phase II/III randomized controlled study tested ultra-high-dose methylcobalamin against placebo[4]. The ALSUntangled group reviewed the evidence on methylcobalamin in 2015[7], and a later multicenter phase 3 trial in Japan focused specifically on patients enrolled within one year of symptom onset[8].

## Mechanisms Studied in Research

The established biochemical role of methylcobalamin is as the methyl-carrying cofactor of B12-dependent methyltransferases; additional neural mechanisms have been proposed from experimental studies. In humans, cobalamin is converted via methionine synthase and methylmalonyl-CoA mutase into its two cofactor forms[1].Proposed neural mechanisms include:
- Nerve regeneration and neuroprotection: promoting regeneration of injured nerves and antagonizing glutamate-induced neurotoxicity[9].
- Reduced ectopic firing: inhibiting spontaneous ectopic discharges of injured primary sensory neurons[9].
- Ion channel modulation: decreasing excitability in medium-sized dorsal root ganglion neurons and the expression of TRPA1, TRPM8, TRPV1, TRPV4, phosphorylated p38 MAPK and axonal voltage-gated sodium channels[10].
- Immune modulation: effects on T lymphocytes, natural killer cells and cytokines such as TNF-alpha, IL-6 and IL-1beta[10].A 2020 systematic review summarized the proposed basis for B12 in neuropathic pain as promoting myelination, increasing nerve regeneration and decreasing ectopic nerve firing[11]. A 2013 review added that methylcobalamin alleviated pain behaviors in experimental and clinical studies of diabetic neuropathy, low back pain and neuralgia, and improved nerve conduction[9]. Most of these mechanisms come from animal and cell studies.

## Key Findings From Published Studies

Randomized trials of methylcobalamin have produced positive results in some neuropathy and supportive-care settings and mixed results in ALS.
### Neuropathy
In a 1-year double-blind trial in 90 adults with type 2 diabetes on long-term metformin, diabetic neuropathy and B12 levels below 400 pmol/L, oral methylcobalamin raised B12 levels and improved vibration perception threshold, sural nerve conduction, pain scores and quality of life compared with placebo, while several measures worsened in the placebo group[12]. A 2008 review reported that mecobalamin monotherapy and combined therapy both lowered plasma or serum homocysteine and improved neuropathic symptoms, with combinations with other B vitamins appearing more effective[2]. A 2025 meta-analysis of seven randomized trials of dapagliflozin combined with methylcobalamin in diabetic peripheral neuropathy reported improved overall effective rate and nerve conduction velocities[13]. A 2020 systematic review of 24 studies found some evidence for B12 in post-herpetic neuralgia (level II) and painful peripheral neuropathy (level III)[11].
### Amyotrophic lateral sclerosis
In the phase II/III study of 373 patients, which compared two methylcobalamin dose levels with placebo, neither primary endpoint (time to death or full ventilation support, and change in ALSFRS-R score) differed significantly. Post-hoc analyses of patients enrolled within 12 months of onset showed a longer time to primary events and smaller ALSFRS-R decline, and treatment-related adverse events were similar and low across groups[4].The follow-up phase 3 trial enrolled patients diagnosed within one year of onset and, after a 12-week observation period, randomized 130 of them to methylcobalamin or placebo for 16 weeks, with change in ALSFRS-R total score as the primary endpoint[8].
### Hand-foot syndrome
In a 2025 phase 3 trial in 234 women receiving adjuvant capecitabine for HER2-negative early breast cancer, grade 2 or higher hand-foot syndrome occurred in 14.5% of the oral methylcobalamin group and 29.1% of the placebo group, with no methylcobalamin-specific adverse events[5]. Reduction or discontinuation of capecitabine because of hand-foot syndrome occurred in 7.7% versus 13.7%, a difference whose confidence interval included zero[5].Because methylcobalamin's cobalt-carbon bond is light-sensitive, researchers typically confirm identity and purity, including hydroxocobalamin content, with HPLC and mass spectrometry certificates of analysis.Because methylcobalamin's cobalt-carbon bond is light-sensitive, researchers typically confirm identity and purity, including hydroxocobalamin content, with HPLC and mass spectrometry certificates of analysis.

## Regulatory and Research Status

Methylcobalamin is not an FDA-approved drug in the United States, although mecobalamin is approved as a prescription drug in Japan. Cyanocobalamin, not methylcobalamin, is the B12 form used in US-approved prescription products.Reviewers continue to call for better evidence. The 2008 mecobalamin review concluded that more precise double-blind randomized trials were needed to confirm effects on hyperhomocysteinemia, peripheral neuropathy and cardiovascular, neurological and osteoporotic outcomes[2]. Diagnostic questions also complicate research: serum B12 remains the most common test, but holotranscobalamin, methylmalonic acid and homocysteine are increasingly used, and test limitations can lead to inappropriate treatment decisions[1].For researchers, open questions include which patient subgroups benefit in ALS and neuropathy, and how stability differences between B12 forms affect product quality[3].

## FAQ

**Is methylcobalamin the same as mecobalamin?**
Yes. Mecobalamin is the International Nonproprietary Name for methylcobalamin. Both refer to the vitamin B12 form in which a methyl group is bonded to the central cobalt atom, with the formula C63H91CoN13O14P and CAS number 13422-55-4. The name mecobalamin is common in clinical literature from Japan and China.

**What is the molecular weight of methylcobalamin?**
Methylcobalamin has a molecular weight of 1344.4 g/mol according to PubChem (CID 10898559). Its molecular formula is C63H91CoN13O14P. It is slightly lighter than cyanocobalamin (1355.4 g/mol) because a methyl group replaces the cyanide ligand on cobalt, removing one nitrogen and adding three hydrogens.

**How is methylcobalamin different from cyanocobalamin?**
Methylcobalamin is an active coenzyme form of vitamin B12 that serves methyltransferases such as methionine synthase directly. Cyanocobalamin carries a cyanide ligand instead and must be converted in cells before use. Cyanocobalamin is more stable, while methylcobalamin's cobalt-carbon bond is broken by light, which requires light-protected handling.

**Is methylcobalamin FDA approved?**
No. Methylcobalamin is not an FDA-approved drug in the United States. Under the name mecobalamin it is approved as a prescription drug in Japan. US prescription vitamin B12 products use cyanocobalamin. Clinical trials of methylcobalamin, including phase 3 trials in ALS and hand-foot syndrome, have been conducted in Japan and China.

**What does the research on methylcobalamin show?**
Randomized trials report improvements in nerve function and pain measures in diabetic neuropathy and a lower rate of capecitabine-associated hand-foot syndrome versus placebo. In a large phase II/III ALS study, the primary endpoints were not met overall, though post-hoc analyses suggested benefit in patients enrolled early after symptom onset.

**Why is methylcobalamin sensitive to light?**
Methylcobalamin contains a direct bond between cobalt and a methyl carbon. Light energy breaks this cobalt-carbon bond, and in the presence of oxygen the molecule converts to hydroxocobalamin. This photolability is why methylcobalamin is stored and analyzed under light protection, and why stability is a major topic in B12 product research.

## References

1. Sobczyńska-Malefora A, Delvin E, McCaddon A, et al. Vitamin B12 status in health and disease: a critical review. Diagnosis of deficiency and insufficiency - clinical and laboratory pitfalls. Critical reviews in clinical laboratory sciences 2021. PMID: 33881359
2. Zhang YF, Ning G. Mecobalamin. Expert opinion on investigational drugs 2008. PMID: 18491996
3. Temova Rakuša Ž, Roškar R, Hickey N, et al. Vitamin B12 in Foods, Food Supplements, and Medicines-A Review of Its Role and Properties with a Focus on Its Stability. Molecules (Basel, Switzerland) 2022. PMID: 36615431
4. Kaji R, Imai T, Iwasaki Y, et al. Ultra-high-dose methylcobalamin in amyotrophic lateral sclerosis: a long-term phase II/III randomised controlled study. Journal of neurology, neurosurgery, and psychiatry 2019. PMID: 30636701
5. Xia Y, Zhu Y, Ling L, et al. Effect of methylcobalamin on capecitabine induced hand-foot syndrome in patients with HER2 negative early breast cancer: multicentre, double blind, randomised, placebo controlled, phase 3 trial. BMJ (Clinical research ed.) 2025. PMID: 40935571
6.  Methylcobalamin. Alternative medicine review : a journal of clinical therapeutic 1998. PMID: 9855571
7.  ALSUntangled No. 30: methylcobalamin. Amyotrophic lateral sclerosis & frontotemporal degeneration 2015. PMID: 26203660
8. Oki R, Izumi Y, Fujita K, et al. Efficacy and Safety of Ultrahigh-Dose Methylcobalamin in Early-Stage Amyotrophic Lateral Sclerosis: A Randomized Clinical Trial. JAMA neurology 2022. PMID: 35532908
9. Zhang M, Han W, Hu S, et al. Methylcobalamin: a potential vitamin of pain killer. Neural plasticity 2013. PMID: 24455309
10. Ramadhani A, Astuti I, Widiastuti MG, et al. Methylcobalamin as a candidate for chronic peripheral neuropathic pain therapy: review of molecular pharmacology actiona. The Korean journal of pain 2024. PMID: 39344358
11. Julian T, Syeed R, Glascow N, et al. B12 as a Treatment for Peripheral Neuropathic Pain: A Systematic Review. Nutrients 2020. PMID: 32722436
12. Didangelos T, Karlafti E, Kotzakioulafi E, et al. Vitamin B12 Supplementation in Diabetic Neuropathy: A 1-Year, Randomized, Double-Blind, Placebo-Controlled Trial. Nutrients 2021. PMID: 33513879
13. Deng XL, Wu R, Lin XX, et al. Dapagliflozin combined with methylcobalamin in the treatment of type 2 diabetes mellitus with peripheral neuropathy: a systematic review and meta-analysis. Frontiers in endocrinology 2025. PMID: 40612436