Vitamin B12
Vitamin B12 (cobalamin)
What is Vitamin B12?
Vitamin B12: Cobalamin (cyanocobalamin, methylcobalamin, hydroxocobalamin), an essential water-soluble vitamin (not a peptide) needed for red blood cell formation, DNA synthesis, myelin and methionine/homocysteine metabolism. The sources cited here most often discuss it for: Treats B12 deficiency; Protects nerves in deficiency; Clearer thinking when deficient. Evidence label: Approved (specific use).
- Type
- Not a peptide
- Family
- Lipotropics & Nutrients
- Evidence label
- Approved (specific use) (5 of 5)
- Regulatory status
- Cyanocobalamin injection is a prescription drug whose US label covers vitamin B12 deficiency due to malabsorption, such as pernicious anemia; energy and weight-loss uses are not labeled indications.
- Goals discussed
- Energy & Endurance, Nerves & Pain, Focus & Cognition
- Also called
- cyanocobalamin, cobalamin, methylcobalamin, hydroxycobalamin, adenosylcobalamin, Vitamin B-12, B-12 shots, B12 injections
- Last reviewed
- 2026-10-11
- Cobalamin (cyanocobalamin, methylcobalamin, hydroxocobalamin), an essential water-soluble vitamin (not a peptide) needed for red blood cell formation, DNA synthesis, myelin and methionine/homocysteine metabolism; FDA-approved injectable/oral forms for B12 deficiency and pernicious anemia.1
Regulatory status Cyanocobalamin injection is a prescription drug whose US label covers vitamin B12 deficiency due to malabsorption, such as pernicious anemia; energy and weight-loss uses are not labeled indications. 2
And unless you have low vitamin B-12 levels in your body, vitamin B-12 shots aren't likely to give you more energy or improve your performance.
Mayo Clinic expert answer on B12 shots promoted for weight loss and energy.
What is Vitamin B12 researched for?
The three outcomes most discussed for Vitamin B12 in the sources below, as those sources report them. humanpeptides.fyi makes no claims of its own: a listed benefit can be unproven or can have failed in trials, and the label on each line says which.
Treats B12 deficiency
What do researchers and users say about Vitamin B12?
Vitamin B12 deficiency that is allowed to progress for longer than 3 months may produce permanent degenerative lesions of the spinal cord.
Precautions section of the US prescription label for cyanocobalamin injection.
Yes oh my god I feel exhausted after my injections. My body aches
Reply in a thread where several people with diagnosed deficiency describe fatigue and aches after injections.
What side effects of Vitamin B12 are reported?
- Very safe; no Tolerable Upper Intake Level set (NIH ODS)1
- Some users report headaches, palpitations or transient fatigue during loading dosesanecdotal10
- Anaphylactic shock and death have been reported after injected vitamin B12.FDA label2
- Low potassium (hypokalemia) and sudden death may occur when severe megaloblastic anemia is treated intensively.FDA label2
- People with early Leber's disease (hereditary optic nerve atrophy) treated with cyanocobalamin developed severe, rapid optic atrophy.FDA label2
- Some observational studies link high blood B12 levels or long-term high-dose supplements with higher cancer risk, though trial evidence has not confirmed this.observational, mixed evidence11
What do peptide guides say about Vitamin B12?
- NIH Office of Dietary Supplements NIH says B12 supplements do not appear to improve athletic performance or endurance in people whose B12 status is already adequate. 11
- NIH Office of Dietary Supplements NIH calls the B12 and cancer evidence mixed: some observational data link high blood B12 to cancer, while a meta-analysis of 18 trials found little or no effect on cancer incidence. 11
- NIH Office of Dietary Supplements A Cochrane review cited by NIH found high-dose oral B12 normalized blood levels about as well as injections, though the evidence was low quality. 11
- Mayo Clinic Mayo Clinic says there is no solid proof B12 shots help weight loss, and notes metformin can lower B12 levels. 9
- DailyMed (FDA label) The label warns that folic acid can correct the anemia of B12 deficiency while nerve damage keeps progressing, so folate cannot substitute for B12. 2
What does the research say, system by system?
Body & tissues1
Hormones & physiology1
- Cofactor converting homocysteine to methionine and methylmalonyl-CoA to succinyl-CoA; MMA is a sensitive deficiency marker; deficiency risk with metformin, PPIs, older age, vegan diet (NIH ODS)1
Cells & mitochondria1
- Required for mitochondrial methylmalonyl-CoA mutase (propionate/odd-chain fat metabolism) (NIH ODS/StatPearls)4
Brain, mood & sleep2
Weight & metabolism1
- No evidence B12 itself causes weight loss in non-deficient peopleno supporting trials found1
Also notable1
- Extra B12 did not reduce fatigue in IBS/IBD patientsRCT14
How strong is the evidence for Vitamin B12?
FDA-approved/strong evidence for deficiency; little to no benefit shown in non-deficient people
Approved by the FDA (or a major regulator) for at least one specific use. Approval covers that use only, not the other benefits listed. How tiers work
Questions about Vitamin B12
What is Vitamin B12?
Cobalamin (cyanocobalamin, methylcobalamin, hydroxocobalamin), an essential water-soluble vitamin (not a peptide) needed for red blood cell formation, DNA synthesis, myelin and methionine/homocysteine metabolism.
Is Vitamin B12 FDA-approved?
Cyanocobalamin injection is a prescription drug whose US label covers vitamin B12 deficiency due to malabsorption, such as pernicious anemia; energy and weight-loss uses are not labeled indications.
What is Vitamin B12 researched for?
The sources cited on this page most often discuss three outcomes: Treats B12 deficiency; Protects nerves in deficiency; Clearer thinking when deficient. Each line above shows what the source reports and how strong that evidence is.
What side effects of Vitamin B12 are reported?
Reported in the cited sources: Very safe; no Tolerable Upper Intake Level set (NIH ODS); Some users report headaches, palpitations or transient fatigue during loading doses; Anaphylactic shock and death have been reported after injected vitamin B12. The list is not complete, and few listed risks does not mean a compound is safe.
How strong is the evidence for Vitamin B12?
Evidence label: Approved (specific use). FDA-approved/strong evidence for deficiency; little to no benefit shown in non-deficient people.
What else is Vitamin B12 called?
Names used for it include cyanocobalamin, cobalamin, methylcobalamin, hydroxycobalamin, adenosylcobalamin, Vitamin B-12, B-12 shots, B12 injections.
Does humanpeptides.fyi recommend Vitamin B12?
No. humanpeptides.fyi makes no claims and no recommendations of its own. It summarizes and links to what others have published and posted. Nothing here is medical advice; talk to a licensed clinician.