Other adverse reactions include: Central Nervous System: Drowsiness, mental clouding, lethargy, impairment of mental and physical performance, anxiety, fear, dysphoria, psychic dependence, mood changes. Tell your doctor immediately if any of these highly unlikely cheap hydrocodone usa but very serious side effects occur: impairment or loss of hearing especially with high doses for long periods. Hydrocodone exhibits complex pattern of metabolism including O- demethylation, N-demethylation and 6-keto reduction to the corresponding 6- and 6- hydroxymetabolites. Hydrocodone is narcotic pain reliever opiate-type that acts on certain centers in the brain to give you pain relief.