Methylcobalamin is the form of vitamin B12 active in the central nervous system. It is essential for cell growth and replication.96 In some people the liver may not convert cyanocobalamin, the common supplemental form of vitamin B12, into adequate amounts of methylcobalamin needed for proper neuronal functioning.92 Methylcobalamin may exert its neuroprotective effects through enhanced methylation, acceleration of nerve cell growth, or its ability to maintain already healthy homocysteine levels.97 For methylcobalamin to be available to the brain, it should be allowed to dissolve in the mouth.