Most of the B12 on the shelves at your grocery store is cyanocobalamin, which is not natural.
From the blogs.psychcentral.com
Hydroxycobalamin reacts with cyanide to form cyanocobalamin, which can be eliminated by the kidneys.
From the en.wikipedia.org
Cyanocobalamin is the form used, and unfortunately, the body can form harmful cyanide byproducts when it breaks this chemical down.
From the healthland.time.com
Vegans can obtain B12 by taking a supplement or by eating fortified foods, such as fortified soy milk or cereal, where it may be listed as cobalamin or cyanocobalamin.