How long alcohol stays in your system depends on how much you drank, your metabolism, your overall health, and whether you take certain medications. In general, alcohol can take up to about 25 hours to be completely eliminated from the body.
Alcohol is processed mainly by the liver, but this happens at a limited, steady rate. As the body breaks down alcohol, it also produces byproducts that are responsible for hangover symptoms, and these also need time to be cleared from the body.