Vitamin B12 Injection Dosage: 1mg Protocol

The documented vitamin B12 protocol is 1000 mcg (1 mg) injected SubQ or IM on a loading schedule — alternate days to three times weekly for roughly four weeks — then stepped down to weekly or monthly maintenance. On the common 10 mg research vial with 2 mL of bacteriostatic water, each 1 mg dose draws as 20 units on an insulin syringe.

Research-context information only. Vitamin B12 (cobalamin) is the active ingredient in FDA-approved injectable products for vitamin B12 deficiency, including pernicious anemia; research vials and compounded forms are not FDA-approved and are sold for research purposes only. Protocols, doses, and reactions reported below come from clinical trials and community sources. This article reports what has been documented, not what should be done. Consult a licensed physician for personal medical decisions.

Vitamin B12 is an essential water-soluble vitamin required for red-blood-cell formation, DNA synthesis, and neurological function. This guide covers the documented injection schedules, the oral-versus-injection evidence, and the syringe math per vial size.

Quick Reference: Documented Protocol

Documented protocol: 1 mg three times weekly for 4 weeks, then 1 mg weekly to monthly. The clinical trial schedule this simplifies from (Kuzminski 1998) dosed 1 mg on days 1, 3, 7, 10, 14, 21, 30, 60 and 90.

Cycling Details

B12 is not cycled the way research peptides are. Documented protocols run a front-loaded repletion phase until levels recover, then hold a maintenance frequency — weekly in community protocols, monthly in the classical clinical pattern. Where the underlying cause is an absorption disorder (pernicious anemia, post-GI-surgery), published guidance describes maintenance as ongoing rather than time-boxed (Stabler, 2013).

There is no documented off-phase requirement: B12 is water-soluble, and clinical reviews report no established upper limit, with excess excreted renally.

Routes of Administration

Intramuscular (IM). The classical clinical route in trials and approved-product labeling. Deltoid or ventrogluteal in published practice.

Subcutaneous (SubQ). Widely used in community protocols and described as comparable for cobalamin absorption. Smaller needle, abdominal or thigh sites in self-reported use.

High-dose oral / sublingual (1-2 mg daily). Backed by randomized-trial evidence — see "Where These Numbers Come From." The documented route where injections are not warranted.

Reconstitution Quick Reference

Research vendors ship B12 either as a ready-made solution (no mixing) or as a lyophilized vial. For lyophilized vials, the common math:

10 mg vial + 2 mL BAC = 5 mg/mL. 1 mg = 0.2 mL = 20 units. The dilution above reflects how community reconstitution protocols describe the math, not a set of instructions to follow.

Swirl gently — do not shake. Refrigerate at 2-8°C, protect from light (cobalamin is photosensitive), and use within 28 days.

Ready to buy? Compare verified vendors on our best B12 sources page, or browse all coupon codes for up to 50% off.

Affiliate disclosure: vendor links in this article are affiliate links — The Peptide Catalog may earn a commission if you buy through them, at no additional cost to you.

Where These Numbers Come From

The 1 mg unit is not arbitrary — it is the dose used across the deficiency-correction literature. The randomized trial by Kuzminski et al., 1998 assigned newly diagnosed cobalamin-deficient patients to 1 mg IM on days 1, 3, 7, 10, 14, 21, 30, 60 and 90, against 2 mg oral daily. Both arms corrected hematologic and neurologic abnormalities; the oral arm finished with higher serum B12 at four months (1,005 vs 325 pg/mL).

That oral finding replicated at scale: the pragmatic OB12 trial in primary care reported oral B12 non-inferior to intramuscular dosing for deficiency treatment (Sanz-Cuesta et al., 2012 — Project OB12). Roughly 1% of an oral dose absorbs passively, independent of intrinsic factor — which is why 1-2 mg oral can match injections even in pernicious anemia.

The clinical review anchoring modern practice (Stabler, 2013, NEJM) describes the loading-then-maintenance shape used above and the populations where injection remains first-line: severe neurologic involvement, absorption disorders, and post-surgical states.

Form matters less than the mcg amount. Cyanocobalamin is the form in most approved products and trials; methylcobalamin — the active coenzyme form most research vendors sell — is dosed identically, and the body converts cyanocobalamin readily.

Stacking Protocols

B12 appears in community wellness stacks alongside other injectable cofactors:

These are reported combinations, not documented synergies — no trial has tested the stacks.

Side Effects & Safety

• Injection-site soreness or redness — the most commonly reported reaction
• Mild acne flare, reported at high frequencies of dosing
• Very low systemic toxicity; no tolerable upper intake level established in clinical reviews
• Hypokalemia has been reported during rapid correction of severe megaloblastic anemia — a clinical-monitoring context
• Cobalt sensitivity (rare) — cobalamin contains a cobalt core
• Documented caution: B12 supplementation can mask folate-deficiency anemia on bloodwork

mg to Units Conversion

On a standard U-100 insulin syringe, each unit is 0.01 mL. The conversions below reflect the dilutions documented in community reconstitution protocols — they report how the math is described, not a dosing schedule.

Reconstitution A: 10 mg vial + 2 mL BAC water (5 mg/mL) — the standard dilution from the Quick Reference above.

Reconstitution B: 10 mg vial + 1 mL BAC water (10 mg/mL) — less volume per draw from the same vial.

These conversions reflect the dilutions documented in community reconstitution protocols. They report how the math is described, not a recommended dosing schedule.