Levomefolate magnesium is the magnesium salt of the metabolite of folic acid (Vitamin B9) and it is a predominant active form of folate found in foods and in the blood circulation, accounting for 98% of folates in human plasma. It is transported across the membranes including the blood-brain barrier into various tissues where it plays an essential role in the DNA synthesis, cysteine cycle and regulation of homocysteine, where it methylates homocysteine and forms methionine and tetrahydrofolate (THF). Levomefolate is approved as a food additive and is designated a GRAS (generally regarded as safe) compound. It is available commercially as a crystalline form of the calcium salt (Metafolin(R)), which has the stability required for use as a supplement. Supplementation of levomefolic acid is desired over folic acid due to reduced potential for masking vitamin B12 deficiency symptoms.