Methylcobalamin, an active coenzyme form of vitamin B-12, is essential for cell growth and replication. It is more concentrated than other forms of B-12 in the cerebral spinal fluid where it can be used by the central nervous system. It donates methyl groups to the myelin sheath that insulates certain nerve fibers. It may also play a role in maintaining a healthy sleep-wake cycle, as well as normal nerve function.