From the biochemical point of view, the amount of the enzyme alcohol dehydrogenase in a person’s body determines how rapidly their body can process alcohol. People with more alcohol dehydrogenase can convert ethanol (which is what gets you drunk) to acetaldehyde faster. A person’s body size also is important, though. Bigger people have more mass to spread the alcohol around so their blood concentration of ethanol doesn’t rise as fast as that of smaller people.