Form Comparison

Adenosylcobalamin vs Methylcobalamin

How adenosylcobalamin and methylcobalamin differ in potency, absorption, tolerance, and cost.

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Quick verdict. These are the two active coenzymes: methylcobalamin works in the cytosol for methionine synthase, adenosylcobalamin in mitochondria for methylmalonyl-CoA mutase. Oral doses of either are stripped and rebuilt into both cofactors inside cells, so taking one does not starve the other pathway. Methylcobalamin has more human data; choose it alone or in a combination, but do not pay extra expecting adenosylcobalamin to fix something methylcobalamin cannot.

Side by Side

Adenosylcobalamin Methylcobalamin
Absorption Moderate High
How it is absorbed Same uptake pathways. Mitochondrial cofactor for methylmalonyl-CoA mutase. Same intrinsic factor and passive diffusion pathways as cyanocobalamin. Cofactor for methionine synthase in the cytosol.
Typical dose 500-1,000 mcg daily, often combined with methylcobalamin 500-1,000 mcg daily
Common uses combination B12 products general supplementation, neuropathy (limited evidence)
Side effects Very well tolerated. Very well tolerated.
Cost High Moderate
Also called dibencozide, cobamamide methyl B12, mecobalamin
Labels in index 115 848

When to Choose Adenosylcobalamin

Choose adenosylcobalamin when it is part of a combined methyl and adenosyl product you already want. Human data comparing it to other oral forms are sparse.

Adenosylcobalamin

Choose adenosylcobalamin when it is part of a combined methyl and adenosyl product you already want.

What to look for: Adenosylcobalamin named on the Supplement Facts panel, with the amount per serving stated.

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When to Choose Methylcobalamin

Choose methylcobalamin when you prefer a cyanide-free active form and accept a modest premium. Less stable to light. Cells strip the methyl group on uptake and rebuild both active cofactors, so the form taken matters less than the dose.

Methylcobalamin

Fine, but not superior. Cells rebuild the active cofactors regardless of the starting form.

What to look for: Light-protective packaging and the same microgram dose you would use for cyanocobalamin.

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Products on Titrate

In Titrate's index of NIH label data, 115 labels named as vitamin B12 products list adenosylcobalamin and 848 list methylcobalamin.

Open supplement search

Supplement Search loads one category at a time. Choose the B-Complex tab, then type a form such as "cyanocobalamin" under Must contain, or a form to avoid under Must not contain.

Related

References

NIH Office of Dietary Supplements. Vitamin B12: Fact Sheet for Health Professionals.

Berlin H, Berlin R, Brante G. Oral treatment of pernicious anemia with high doses of vitamin B12 without intrinsic factor. Acta Med Scand. 1968;184(4):247-258.

Stabler SP. Vitamin B12 deficiency. N Engl J Med. 2013;368(2):149-160.

Lam JR, et al. Proton pump inhibitor and histamine 2 receptor antagonist use and vitamin B12 deficiency. JAMA. 2013;310(22):2435-2442.

Aroda VR, et al. Long-term Metformin Use and Vitamin B12 Deficiency in the Diabetes Prevention Program Outcomes Study. J Clin Endocrinol Metab. 2016;101(4):1754-1761.

Wang H, et al. Oral vitamin B12 versus intramuscular vitamin B12 for vitamin B12 deficiency. Cochrane Database Syst Rev. 2018;3(3):CD004655.