The most common form of B-12 in vitamin supplements is cyanocobalamin and although this form includes a cyanide molecule, it is very safe. Why? Even at a very high dose, it would provide about a thousand times less cyanide than is toxic, and the cyanide is excreted in the urine. B-12 is also available in supplements as methylcobalamin. Supplements with both types of B-12 are included in the Product Review of B Vitamins.