The MEOS (microsomal ethanol oxidizing system) is an accessory pathway in the liver which increases in activity on chronic alcohol induction. The MEOS utilizes a cytochrome P450 which has since been deciphered to be CYP2E1, an ethanol-inducible form of P450. CYP2E1 also increases acetaldehyde formation and free radicals which can initiate lipid peroxidation. CYP2E1 can also activate many over-the-counter medicines and solvents to toxic metabolites and deplete retinoids resulting in their depletion and deletrious effects. This is because, being a cytochrome P450 and using NADPH and oxygen, it has the ability to biotransform drugs when it has been induced by ethanol.