L-Methylfolate is the centrally active derivative of the vitamin folate and is used for both neurotransmitter synthesis, and vital methylation reactions in all cells. It regulates BH4 (or tetrahydrobiopterin) a critical enzyme cofactor required for serotonin, dopamine and norepinephrine synthesis. Some forms of depression resistant to antidepressant treatment may respond to folate or l-methylfolate. Synthesis of the monoamine neurotransmitters serotonin, dopamine, and norepinephrine is regulated by L-methylfolate, a derivate of the vitamin folate. Copyright 2008 Physicians Postgraduate Press, Inc.