Researchers at Victoria University in New Zealand have found that being drunk is partly in the mind. A group of students were given water to drink in a pub-like environment; half were told it was vodka, and the other half were told the truth. The candidates were then shown slides of a crime and asked to assess a story full of misleading information. The students who thought they were drinking vodka had poorer memory and were more suggestible and less reliable as witnesses.
(Which shows that if you believe (from external evidence) that you should be drunk or perceptually impaired, your brain will go out of its way to induce this state, to the point of subconsciously degrading your perception appropriately. Which makes one wonder: what proportion of people's inabilities to achieve various things is the result of suggestion or conditioning, with no physical basis?)