Alcohol dehydrogenase is a zinc-containing enzyme that catalyzes the reversible conversion of acetaldehyde and ethanol using NADH / NAD⁺. See below.

Alcoholic fermentation depends on the enzyme to produce ethanol under anaerobic conditions. Production of acetaldehyde by reversal of the reaction by the liver enzyme may be responsible for the "hangover" felt after drinking too much alcohol.

Acetaldehyde + NADH + H⁺ <=> Ethanol + NAD⁺