"Since the lungs have to work harder to get oxygen into the blood in high altitudes, alcohol is absorbed into the blood system quicker, speeding up the effect that a couple of drinks would normally have. The bottom line — two or three drinks in Denver will pack more of a wallop than at sea level."

Source: Denver Metro Convention & Visitors Bureau "DENVER TRULY IS A MILE HIGH – And High Altitude Can Play Some Interesting Tricks"