Vitamin B12 (cobalamin)
Essential vitamin, also called cobalamin, used in DNA synthesis and cell metabolism; research centers on deficiency.
What it is
The body converts B12 into coenzyme forms needed to turn methylmalonate into succinate and to make methionine from homocysteine, a step that also needs folate. Through these reactions B12 supports DNA synthesis, methylation and mitochondrial metabolism.
What it is studied for
Research focuses on B12 deficiency, which can come from low intake, poor absorption or malabsorption and is most common in older adults. Trials have compared high-dose oral B12 with injections, and one trial tested extra B12 for fatigue in people with normal levels.
What the evidence says
Human trials, mainly in deficiency
A Cochrane review of 3 small trials found low-quality evidence that high-dose oral and injected B12 similarly normalize blood levels in deficiency. In 95 people with bowel disorders, fatigue and normal B12, daily B12 did not ease fatigue more than placebo. A 2026 survey found little justification for adding nutrients such as B12 to injectable tirzepatide or semaglutide.
How it was studied
Studied routes include injection into muscle, high-dose oral B12 and a prescription nasal spray. Capsules combining B12 with tirzepatide were not the form studied.
Regulatory status
Prescription B12 products have specific approved uses. Nascobal (cyanocobalamin nasal spray), for example, is FDA-approved to treat or prevent B12 deficiency in defined adult groups, including maintenance in pernicious anemia after injection therapy.
Where to find it
Tirzepatide / B12
- Capsules Tirzepatide 1 mg and B12 1 mg per capsule, 30 capsules
- Capsules Tirzepatide 2 mg and B12 1 mg per capsule, 30 capsules
Sold by USA Standard Research, the team behind PeptidesGenie, for research use only. Not for human or veterinary use.
Sources
- 1Green et al. (2017): Vitamin B12 deficiency Expert review
- 2Wang et al. (2018): Oral vitamin B12 versus intramuscular vitamin B12 for vitamin B12 deficiency Systematic review of randomized trials
- 3
- 4Nascobal prescribing information US prescription label
- 5Belcourt et al. (2026): Compounded Semaglutide and Tirzepatide Products Use Unique Formulations but Efficacy and Safety Largely Unknown Survey of compounded products (journal editorial)
Source-checked · 27 Oct 2026