Overview
Methylcobalamin is one of the two coenzymatically active forms of vitamin B12 (the other being adenosylcobalamin). It is included in this library because injectable B12 — methylcobalamin or cyanocobalamin — is the single most commonly stacked companion compound with peptides, and because methyl-B12 supports methylation pathways that intersect with most peptide protocols. Tier diverges sharply by indication: replacing a documented B12 deficiency or treating pernicious anemia is straightforward Tier 1 nutritional medicine. Using B12 injections as a generic 'energy boost' in non-deficient adults — the wellness-clinic market — has no controlled-trial support. Editorially this entry must hold the line on the indication split.
Mechanism
B12 is the cofactor for two essential enzymes: methionine synthase (uses methylcobalamin to remethylate homocysteine to methionine, supporting SAMe-dependent methylation of DNA, RNA, neurotransmitters, and phospholipids) and L-methylmalonyl-CoA mutase (uses adenosylcobalamin in mitochondrial fatty acid metabolism). The methyl form is preferred by some practitioners for users with MTHFR variants, though the practical clinical relevance of MTHFR genotype to B12 form choice is contested.
Evidence by indication
We classify each indication separately. The same peptide can be Tier 1 for one use and Tier 4 for another. Tiers reflect the published literature, not the strength of community framing.
Vitamin B12 deficiency / pernicious anemia
Standard nutritional medicine since the 1940s. IM/SubQ replacement reverses megaloblastic anemia and neurological deficits. WHO and national guidelines recommend parenteral B12 for symptomatic deficiency and for malabsorption (intrinsic factor deficiency, post-bariatric, ileal disease).
B12 deficiency on metformin / PPI / vegan diet
Documented increased risk of B12 deficiency on chronic metformin (Aroda et al., DPPOS) and PPI use, and in long-term vegans. Replacement is well established; the Tier 1 evidence is for replacement specifically when deficiency is documented or strongly suspected by lab markers (B12, MMA, homocysteine).
Subacute combined degeneration of the spinal cord
Established neurological complication of severe B12 deficiency; parenteral repletion is the treatment of record.
Generic 'energy boost' in non-deficient adults (wellness-clinic IM)
There is no published RCT showing that B12 injections in non-deficient adults improve energy, cognition, or fatigue. The IM/IV B12 market in wellness clinics rests almost entirely on placebo and the experience of being injected. Hold this Tier 3 firmly, despite massive consumer-clinic volume.
No primary citations are anchored to this indication — the tier reflects the absence of usable literature, not a missing reference.
Cognitive function / dementia prevention in normal-B12 elderly
B12 supplementation in adults without documented deficiency has not been shown to prevent cognitive decline in well-designed RCTs (e.g., VITACOG and others). Replacement IS warranted when deficiency is found; supplementation as a general cognitive intervention is not supported.
No primary citations are anchored to this indication — the tier reflects the absence of usable literature, not a missing reference.
Diabetic peripheral neuropathy (high-dose methylcobalamin)
Multiple Asian RCTs of high-dose oral or parenteral methylcobalamin in diabetic neuropathy show modest symptom improvement. Studies are heterogeneous and effect sizes modest. Tier 2 with appropriate caveats.
Studied dose ranges
The ranges below come from published trial protocols where available, and from documented self-experimenter consensus where the literature does not include human dose-finding work. The notes flag which is which.
Standard pernicious anemia / B12 deficiency replacement is 1000 mcg IM weekly for 4–8 weeks, then monthly maintenance. Many wellness clinics use 1000 mcg weekly indefinitely; this is a dosing convention, not a deficiency requirement.
Oral 1000–2000 mcg daily can correct deficiency in many cases by mass action, even when intrinsic factor is impaired (passive diffusion absorbs ~1%).
Contraindications
- Known hypersensitivity to cobalt or formulation excipients (rare)
- Leber's hereditary optic neuropathy (cyanocobalamin specifically; methylcobalamin is safer in this rare condition)
- Polycythemia vera (theoretical caution; correcting megaloblastic anemia can unmask increased red-cell mass)
Reported side effects
- Generally extremely well tolerated
- Injection-site discomfort, transient erythema
- Rare: anaphylactoid reaction (more historically associated with cyanocobalamin formulations containing aluminum)
- Rare: acneiform eruption with high-dose injection in some users
- Hypokalemia possible during rapid correction of severe megaloblastic anemia (treat-the-cause warning, not a routine concern)
Reconstitution & storage
Methylcobalamin for IM/SubQ injection is typically supplied as a sterile pre-mixed solution (commonly 1 mg/mL or 5 mg/mL) — no patient reconstitution required for standard pharmacy product. Compounded formulations vary; a 1 mg/mL solution makes a standard 1000 mcg dose = 1 mL = 100 units on a U-100 syringe. Methylcobalamin is light-sensitive (reddish-pink color from the cobalt); store amber vial or away from light.
Storage. Refrigerate 2–8 °C, protect from light. Compounded multi-dose vials: use within label expiration. Some methylcobalamin formulations are stable at room temperature short-term but the methyl form degrades faster than cyanocobalamin under light/heat.
Open the peptide calculator → to compute exact draw volumes for your specific vial and BAC water choice.
Editorial note
DRAFT — pending Wayne's review. B12 is in the library because it's the most common companion injection stacked with peptides and because the wellness-clinic 'energy shot' market needs a Tier 3 framing. The class field literally says 'Vitamin (cobalamin) — NOT a peptide' so the badge does the editorial work. Tier 1 for actual deficiency and pernicious anemia; Tier 3 for the energy-shot market. Don't let the deficiency tier propagate to non-deficient users.
Citations
- [1]Guidelines for the diagnosis and treatment of cobalamin and folate disordersDevalia V, Hamilton MS, Molloy AM · British Journal of Haematology · 2014 · PMID 24942828Anchor guideline reference for Tier 1 deficiency / pernicious anemia indication.View source
- [2]Long-term Metformin Use and Vitamin B12 Deficiency in the Diabetes Prevention Program Outcomes StudyAroda VR, Edelstein SL, Goldberg RB, et al. · Journal of Clinical Endocrinology & Metabolism · 2016 · PMID 26900641Tier 1 anchor for the metformin-related B12 deficiency indication; large prospective dataset (DPPOS).View source
- [3]Cobalamin supplementation in the treatment of painful diabetic neuropathy: a systematic review and meta-analysisJayabalan B, Low LL. · Singapore Medical Journal · 2016 · PMID 27293795Anchor for the Tier 2 diabetic peripheral neuropathy indication; mixed evidence with modest effect sizes.View source