Vitamin

Vitamin B12 (Injectable)

Also known as Cyanocobalamin, Methylcobalamin, Hydroxocobalamin, B12 shot, Methyl B12

Injectable vitamin B12 delivers the vitamin straight into muscle or fat, skipping the gut absorption step that limits pills. It's the standard fix for B12 deficiency and a popular weekly add-on in weight-loss protocols for energy and metabolism support.

How one dose clears

modeled over ~6 half-lives

Half-life: 6.0 days
Time to peak (Tmax): 1.0 h
Typical dose: 1000 mcg

Injectable vitamin B12 (usually cyanocobalamin or methylcobalamin), given intramuscularly or deep subcutaneously. Approved for B12 deficiency and pernicious anemia; also widely used in weight-loss and wellness clinics, often weekly.

Mechanism of action

Cofactor for methionine synthase and methylmalonyl-CoA mutase — essential for red blood cell formation, DNA synthesis, myelin maintenance, and energy metabolism. Injection bypasses the intrinsic-factor absorption pathway that limits oral B12.

Water-soluble with low toxicity; excess is excreted in urine within about 48 hours, so much of a large dose isn't retained. The ~6-day half-life models circulating B12 — liver stores last months to years, so blood levels understate how long you stay replete. Rare hypersensitivity reactions reported; hydroxocobalamin is retained longer than cyanocobalamin.

References

DailyMed (cyanocobalamin injection) NIH Office of Dietary Supplements — Vitamin B12

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