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 physiologic stresses, the transformation of folic acid into the active form of folate 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&rsquos risk of having a child with certain brain or spinal cord defects.