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Companion supplement

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Vitamin (cyanocobalamin)

B12 (Cyanocobalamin)

Also known as: Cyanocobalamin, Vitamin B12 — cyanocobalamin form, Crystalline B12, B12 IM

Standard injectable B12 — Tier 1 for B12 deficiency. The cyanocobalamin form is the cheapest and most-shelf-stable; methylcobalamin is preferred by community users for theoretical reasons that do not have strong human-outcome evidence behind them.

Reviewed 2026-05-05

What it does

Cyanocobalamin is the synthetic, crystallized form of vitamin B12 most commonly used in injectable preparations and prescription IM B12 in primary care. It is included in this 'peptide companion' library because B12 — particularly injectable B12 — is widely stacked with peptide regimens (especially GLP-1 / metabolic peptides where appetite suppression risks low B12 intake) and because users routinely ask which B12 form to choose. The companion entry [B12 (Methylcobalamin)](/peptides/b12-methylcobalamin) covers the methylated form preferred in self-injection community practice. The clinical evidence is unambiguous for B12 deficiency itself; the form-preference question (cyano vs methyl) is a real but smaller-stakes editorial conversation rather than a clinical one in most cases.

Used for

Dose

Dose
1,000 mcg · weekly for 4 weeks then monthly
When
MorningActivating; morning timing avoids interference with sleep. Either form absorbs without food, but pair with breakfast for routine adherence.
Site
intramuscular (treatment of established deficiency)

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⚠ Caution

  • Leber's hereditary optic neuropathy (LHON) — cyanocobalamin is contraindicated; can accelerate vision loss. Methylcobalamin or hydroxocobalamin is preferred. This is the single hard form-specific contraindication.
  • Cobalt or cobalamin hypersensitivity
  • Active treatment for cyanide poisoning (cyanocobalamin contains a cyanide group; acute cyanide exposure should use hydroxocobalamin instead)
  • Pregnancy (oral or IM B12 is generally safe in pregnancy at standard doses; cyanocobalamin is the most-studied form)

Your stack

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Use this peptide

Reconstitution & storage

Most prescription cyanocobalamin (1000 mcg/mL) ships as a pre-mixed liquid, no reconstitution needed. Compounded high-concentration formulations may be lyophilized; reconstitute per pharmacy instructions. SubQ injection volumes are typically 0.5–1 mL.

Storage. Pre-mixed liquid: refrigerate per label. Some formulations are stable at room temperature. Protect from light — B12 is photosensitive.

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Monitoring & questions

Reported side effects
  • Injection-site pain, redness, mild swelling (IM more than SubQ)
  • Headache
  • Skin rash, pruritus (rare)
  • Diarrhea, mild GI upset
  • Hypokalemia during rapid correction of severe megaloblastic anemia (clinical-trial-relevant; check potassium during treatment)
  • Anaphylaxis (extremely rare; usually attributed to preservatives in injectable formulations)

Reference

How it works

Cyanocobalamin is converted in vivo to the two metabolically active cobalamin forms — methylcobalamin (cytosolic, methionine synthase cofactor) and adenosylcobalamin (mitochondrial, methylmalonyl-CoA mutase cofactor). The 'cyano' group is replaced during the conversion. The conversion is generally efficient in healthy individuals; rare metabolic errors (cblC, cblG) or severe nitric oxide exposure can impair it.

EvidenceTier 1 — Human RCT

Tiers are per indication. The same molecule can be Tier 1 for one use and Tier 4 for another — the tier reflects published literature, not community framing.

B12 deficiency (pernicious anemia, dietary deficiency, ileal malabsorption, post-bariatric)

Tier 1high confidence

Standard of care for >70 years. Multiple decades of clinical evidence; IM cyanocobalamin reliably reverses biochemical and hematologic markers of B12 deficiency. The pediatric, ileal-resection, and pernicious-anemia populations are clear indications.

Andrès E et al. 2004

Prevention of B12 deficiency in vegan / vegetarian diets

Tier 1high confidence

Plant-based diets are essentially B12-free; supplementation (oral or injectable) is non-negotiable for sustained vegan diets. Standard nutritional recommendation.

No primary citations are anchored to this indication — the tier reflects the absence of usable literature, not a missing reference.

Adjunct in GLP-1 / GIP-GLP-1 peptide stacks (metabolic peptide users)

Tier 3high confidence

Appetite suppression on tirzepatide / semaglutide can reduce B12 intake substantially; metabolic clinics increasingly check B12 status and supplement. The indication is preventive maintenance of normal B12 levels — Tier 1 evidence for that, but 'because of metabolic peptides' is not its own RCT-supported indication.

No primary citations are anchored to this indication — the tier reflects the absence of usable literature, not a missing reference.

Energy / fatigue in B12-replete adults

Tier 4high confidence

IV-clinic and 'B12 shot' marketing positions B12 injections as a general energy boost. There is no RCT showing benefit of B12 in adults with normal B12 levels. The energy effect is a placebo / clinic-context phenomenon for most users.

No primary citations are anchored to this indication — the tier reflects the absence of usable literature, not a missing reference.

Citations (1)
  1. [1]
    Vitamin B12 (cobalamin) deficiency in elderly patients
    Andrès E, Loukili NH, Noel E, et al. · Canadian Medical Association Journal · 2004 · PMID 15289284
    Comprehensive clinical review of B12 deficiency in older adults — anchor for the Tier 1 deficiency indication.
    View source