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B12 (cobalamin) is an essential cofactor for DNA synthesis, myelin formation, red blood cell production, and neurological function. Injectable B12 bypasses gastrointestinal absorption entirely, achieving serum levels 100–1000x higher than oral supplementation — critical for patients with absorption deficits, MTHFR variants, or neurological symptoms.
Commercial B12 injections are available only in cyanocobalamin (the least bioavailable form). Compounding provides methylcobalamin and hydroxocobalamin — the biologically active forms preferred for neurological conditions — along with custom concentrations, multi-B vitamin combinations, and preservative-free formulations for sensitive patients.
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Vitamin B12 (cobalamin) is an essential water-soluble vitamin required for neurological function, DNA synthesis, red blood cell formation, and homocysteine metabolism. Deficiency causes megaloblastic anemia, peripheral neuropathy, cognitive decline, fatigue, and in severe cases, irreversible neurological damage.
Injectable B12 provides dramatically superior bioavailability compared to oral supplementation — bypassing the gastric intrinsic factor-dependent absorption pathway that fails in pernicious anemia, atrophic gastritis, and many GI conditions.
Compounding is valuable because commercial injectables only provide cyanocobalamin, while methylcobalamin and hydroxocobalamin — the active, preferred forms for neurological conditions and patients with MTHFR gene variants — are only available through compounding pharmacies.
Methylcobalamin
The neurologically active form of B12; serves as a cofactor for methionine synthase (converting homocysteine to methionine) and supports myelin synthesis. Preferred for neuropathy and patients with MTHFR variants who have impaired methylation.
Hydroxocobalamin
A depot form that converts to both methylcobalamin and adenosylcobalamin in the body. Longer-lasting than cyanocobalamin, preferred for pernicious anemia and cyanide detoxification.
Cyanocobalamin
The most stable but least biologically active form — must be converted to active forms. Contains a small cyanide molecule released during metabolism (negligible for most patients, but avoided in smokers and renal impairment).
Deficiency States: Pernicious anemia, dietary deficiency (vegan/vegetarian), metformin-induced depletion, PPI-induced depletion, post-bariatric surgery
Neurological: Peripheral neuropathy, cognitive decline, multiple sclerosis support
Energy & Metabolism: Fatigue, MTHFR-related methylation support, athletic performance
Mood: Depression associated with elevated homocysteine or B12 deficiency
Deficiency treatment: 1000mcg IM daily for 7 days, then weekly for 4 weeks, then monthly
Maintenance / optimization: 1000mcg IM or SubQ weekly to monthly depending on indication
Methylcobalamin (neurological): 1000–5000mcg IM 1–3x per week
Dosing frequency varies widely by indication and provider protocol. Self-injection SubQ is common for maintenance.
Common (mild):
Rare:
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