13, 14 VPA—though a cytochrome P450 enzyme inhibitor, in conjunction with other cytochrome P450 enzyme-inducing AEDs such as CBZ and PHN, has high potential to cause folate deficiency and raised homocysteine levels.15, 16 VPA inhibits methionine synthase while other AEDs target methylterahydrofolate reductase inhibiting re-methylation of homocysteine (Figure 1). This evidence concerns the gene MTR and folate deficiency.