Hydroxycobalamin is a precursor form of vitamin B₁₂ converted in the body to both methylcobalamin and adenosylcobalamin. It is similar to cyanocobalamin without the cyanide moiety. Adenosylcobalamin is an activated form similar to methylcobalamin, which is found in the cytosol of cells and predominates in blood and other fluids.

Adenosylcobalamin is the major form of vitamin B₁₂ stored in the mitochondria of cellular tissues and is a key cofactor in carbohydrate metabolism for the enzyme methylmalonyl-CoA mutase used to produce succinyl-CoA. Optimal levels also support healthy synthesis of neuronal myelin.*