Methyl Folate ((6S)-5-methyltetrahydrofolic acid or (6S)-5-MTHF) is the most biologically active form of folic acid. Quatrefolic is the 4th generation development in folate delivery. With certain inherited errors in metabolism and under a variety of physiologic stresses, the transformation of folic acid into the active form of folate either does not properly take place or is inadequate. Unlike folic acid, 5-MTHF can cross the blood-brain barrier. HEALTH CLAIM: Healthful diets with adequate folic acid may reduce a woman’s risk of having a child with certain brain or spinal cord defects.