HBG2 and methemoglobinemia: Normally, methemoglobin reductase enzymes reduce methemoglobin back to functional hemoglobin.[5] However, in some individuals, either due to genetic deficiencies in methemoglobin reductase enzymes or drug interactions inhibiting these enzymes, there is an imbalance between methemoglobin formation and reduction, leading to methemoglobinemia.[6]