From
http://espn.go.com/special/s/drugsandsports/alcohol.html
What effect does alcohol have on performance?
Alcohol is generally not considered to be a performance-enhancing substance, and it has numerous deleterious effects associated with its use. According to Wadler, "Its effects depend upon a number of factors, including how much and how fast one drinks, the individual's size and how much food is in the stomach." The effects of alcohol are directly related to the concentration (percentage) of alcohol in the blood; however, the effects vary among individuals and even in the same individual at different times. Additionally, an acute tolerance may develop whereby increasing amounts are necessary to produce the same effect.
The detrimental effects of alcohol on performance are extremely well documented and include impairment of the following:
Balance and steadiness
Reaction time
Fine and complex motor skills
Information processing
Boisterousness, unsteadiness, slurred speech
Nausea, vomiting, marked unsteadiness, drowsiness
"Additionally, alcohol may impair temperature regulation during prolonged exercise in the cold, and in the heat, its diuretic effect may lead to dehydration," says Wadler. "Poorly appreciated is the fact that athletes who socially consume excessive alcohol the evening after a practice or a game may subsequently have an impairment of athletic skills for as long as 14 hours." Hangovers, the residual or "day-after" effect of alcoholic consumption, can result in symptoms of headaches, nausea, diarrhea, fatigue, dehydration, and body aches that can diminish athletic performance.
I was mistaken about the IOC, they do not consider Alcohol to be a peformance enhancer because of the detrimental effects , despite of its high energy, low fat, protein etc content