Cyanocobalamin (B12)

Cyanocobalamin is an especially common vitamer of the vitamin B₁₂ family. It is the most famous vitamer of the family, because it is chemically the most air-stable, and it is the easiest to crystallize and therefore easiest to purify after it is produced by bacterial fermentation. The cyanide is added to the molecule by activated charcoal columns in purification. Thus, the use of this form of B₁₂ is the most wide-spread.

This fact has caused some people (usually from reading labels on packages and vitamin supplements, in which vitamin B₁₂ is almost always listed last, since ingredients by law are listed in order of weight percentage), to infer that the correct chemical name of vitamin B₁₂ actually is cyanocobalamin. In fact, vitamin B₁₂ is the name for a whole class of chemicals with B₁₂ activity, and cyanocobalamin is only one of these. Cyanocobalamin usually does not even occur in nature, and is not one of the forms of the vitamin which is directly used in the human body (or that of any other animal). However, animals and humans can convert it to active (cofactor) forms of the vitamin, such as methylcobalamin.