Methyl B12 (methylcobalamin), a co-enzyme form of vitamin B12, is the principal circulating form of B12 in the body and the form that is active in the central nervous system. Cyanocobalamin, the form of vitamin B12 most often used in supplements, must be converted to methylcobalamin in a lengthy and sometimes inefficient process. Using high dose (1000 mcg or more) methyl B12 supplements spares the body's resources and ensures that adequate amounts of this active form are available to support nerve function, red blood cell formation, energy production, brain function and homocysteine metabolism.