Vitamin B12 calculator
An essential B vitamin given by injection for deficiency. Not a peptide; well established for treating true deficiency.
Also known as: Cobalamin, Cyanocobalamin, Methylcobalamin
FDA status — not an approved drug Vitamin B12 is an essential nutrient. Injectable B12 is an FDA-approved prescription treatment for deficiency; oral forms are dietary supplements. It is not approved for general energy or weight-loss claims.
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What Vitamin B12 is
Vitamin B12 (cobalamin) is an essential nutrient required for red blood cell production, nerve function, and DNA synthesis. Injectable B12 is an FDA-approved prescription treatment for documented deficiency. It is widely marketed for energy and weight loss, but there is no evidence for those uses in people who are not deficient.
Research depth: 5/5 Essential nutrient, well established for treating true deficiency; no evidence for energy or weight claims in non-deficient people. Human trials: Approved for deficiency. This measures how much has been studied — counting animal and laboratory work — not whether it works for you.
How Vitamin B12 works
B12 is a cofactor for enzymes involved in DNA synthesis, red blood cell formation, and the maintenance of the myelin sheath around nerves. Deficiency causes anemia and neurological damage. Correcting a true deficiency reverses these, but supplementing people who already have adequate levels has no established benefit.
Vitamin B12 side effects
Commonly reported
- Injection-site discomfort
- Generally very well tolerated
- Mild diarrhea or itching reported
Serious — seek medical care
- Very safe even at high doses — excess is excreted
- No established benefit in non-deficient people despite marketing
- Rare allergic reactions to injectable forms
This list is not exhaustive. Report anything unexpected to the clinician who prescribed it. If you have severe abdominal pain, trouble breathing, or signs of an allergic reaction, seek care the same day. See also our guide to peptide side effects by class.
A worked example
A 10 mg vial reconstituted with 10 mL of bacteriostatic water gives 1 mg/mL. A 1000 mcg dose is then 1 mL — about 100 units on a 100-unit insulin syringe, giving roughly 10 doses per vial before accounting for residual volume left in the vial and syringe.
Prefer paper? Download the printable Vitamin B12 dosing chart (PDF) — every vial size and water volume in syringe units, with the same review byline as this page. All charts →
Commonly cited dose range
Figures circulating for Vitamin B12 run from 1000 mcg to 5000 mcg. Injectable B12 is dosed in micrograms (typically 1,000 mcg) on a schedule set by a clinician for documented deficiency. Figures shown are reference points in micrograms.
Read this as reference information, not instruction. These numbers describe what is commonly discussed, not what is right for any individual. Dose, frequency, and whether to use Vitamin B12 at all are decisions for a licensed clinician who knows your history.
Common questions
Is vitamin B12 a peptide?
No. Vitamin B12 (cobalamin) is a vitamin — a cobalt-containing nutrient — not a peptide. It appears on some supplier lists alongside injections but is chemically distinct.
Do B12 injections help with energy or weight loss?
For people with a true B12 deficiency, correcting it can restore energy. For people who are not deficient, there is no good evidence that B12 injections boost energy or cause weight loss, despite their popularity for those purposes.