Vitamin B12
Vitamin B12 (Cobalamin)
Helps if you're a vegan, elderly, or have pernicious anemia. Otherwise no AGA benefit.
How Vitamin B12 works — and how well we know it
Required for DNA synthesis and red blood cell formation. Severe deficiency causes megaloblastic anemia, which can be associated with hair changes through anemia-driven follicle stress.
oral, intramuscular (for deficiency)
2.4 mcg/day (RDA). Supplement marketing often uses 100–5,000 mcg/day; absorption is saturable so most of the high doses are excreted.
Available as a dietary supplement and prescription (for pernicious anemia). RDA 2.4 mcg/day. Common deficiency in vegans, the elderly, and patients with pernicious anemia.
Vegans, elderly patients, and pernicious anemia patients with documented deficiency.
Evidence distribution across 1 claims
Why the grade is D. Deficiency-only correction. Relevant population (vegans, elderly, pernicious anemia patients) is well-defined; supplementing fed omnivores has no AGA benefit.
Every claim, traced back to its source
We took every major claim made about Vitamin B12 and matched it to the specific experimental model behind it. Click a claim to see the model, the finding, and our assessment of how much weight it deserves.
1 claims · evidence-by-evidence breakdown
1Open-LabelWeight: ModerateSevere B12 deficiency anemia can affect hair, but supplementation in non-deficient adults has no evidenceUseful for documented deficiency; no AGA benefit in fed adults.
Clinical literature on B12 deficiency-related anemia and associated hair changes.
Severe deficiency-driven megaloblastic anemia is associated with hair changes. Correction with B12 reverses the underlying anemia. No AGA RCT supports supplementation in non-deficient adults.
Real for the specific deficient populations (vegans, elderly, pernicious anemia). Useless as a generic hair supplement ingredient.
What's still missing from the science
- RCT of B12 supplementation for AGA in non-deficient adults.
Our verdict on Vitamin B12
Not in our formulary yet
We don't carry this ingredient. We only formulate around actives where the evidence — and the safety profile — is strong enough to recommend with confidence. As the data matures, we may revisit.
Related treatments
How does Vitamin B12 stack up against its closest peers?
A genuine cause of reversible hair shedding in iron-deficient patients — but useless and potentially harmful if your iron stores are normal.
Read the breakdown →A botanical 5-alpha reductase inhibitor whose only high-quality trials (in BPH) showed no benefit over placebo; the positive AGA data are small and low-quality.
Read the breakdown →One small Malaysian RCT showed a hair-count increase. Never replicated. Used by Nutrafol to justify its tocotrienol content.
Read the breakdown →