Vitamin B12
Also called Cyanocobalamin; methylcobalamin; hydroxocobalamin
An essential vitamin for red blood cells and nerves. Injections are FDA approved for B12 deficiency and are popular as energy shots, though extra B12 has not been shown to help people with normal levels.
Overview
What it is
A vitamin, not a peptide. Cyanocobalamin injection is the FDA-approved form; methylcobalamin is a natural form that is usually compounded. B12 is also added to many weight-loss and lipotropic injections.
How it works
B12 is a cofactor for two enzymes: one needed to make DNA in new blood cells and one that keeps homocysteine low and nerves myelinated. Deficiency causes a large-cell anemia, fatigue, numbness and memory problems. Injections bypass the gut, which matters for people who cannot absorb B12.
What the research shows
Injections reliably correct deficiency, including pernicious anemia. Studies have found high-dose oral B12 can work as well for many people. Deficiency is more common in older adults, vegans and vegetarians, after gastric bypass, and with long-term metformin or acid-reducing drugs. Trials have not shown that extra B12 boosts energy, mood or weight loss in people whose levels are already normal.
Studied for
- B12 deficiency and pernicious anemiaFDA approved
- Low B12 from metformin, acid reducers or bariatric surgery
- Energy and fatigueno benefit shown without deficiency
Safety and regulatory status
Safety and side effects
Very safe. Injection-site pain and, rarely, allergic reactions, including to cobalt. Cyanocobalamin should not be used in Leber hereditary optic neuropathy. Starting treatment for severe anemia can lower potassium, so providers monitor it.
Regulatory status
Cyanocobalamin injection is an FDA approved prescription medicine. Oral B12 is sold as a dietary supplement. Methylcobalamin injections are compounded.
Common questions
Will a B12 shot give me energy?
If you are low in B12, often yes. If your level is normal, studies have not shown an energy benefit.
Shot or pill?
For most people high-dose pills work. Shots are best when absorption is the problem, such as pernicious anemia or after bariatric surgery.