Hangover impairs judgment

The effects of intoxication last long after the alcohol is out of the blood, not only leaving a nasty hangover but also slowing reaction times and the ability to concentrate the next morning.

Previous research shows that symptoms of a hangover (headache, nausea, sleepiness) usually lift within a few hours of waking. To look at the effects of heavy drinking on young adults, researchers studied 95 Americans between the ages of 21 and 33. The participants spent two nights at the Boston test facility. One night they were given alcohol (either vodka or bourbon mixed in cola) and the other night they were given a placebo. The researchers determined their blood alcohol levels, sleep patterns and ability to think quickly and over a long period of time. Vodka and bourbon appear on each extreme of alcohol purity: vodka has the least impurities while bourbon 37 times more impurities or congeners (byproducts of the fermenting process) - all other alcohols are somewhere in between.

To approximate the effects of drinking on an empty stomach, researchers gave the participants a standardised meal three hours before the test liquids were given until subjects reached a minimum blood alcohol level of 0.09 grams percent (just above the level considered to be legally drunk).  Hangover correlated with poorer performance on tests requiring both sustained attention and speed. Alcohol decreased sleep efficiency and rapid eye movement sleep, and increased wake time and next-day sleepiness. Alcohol effects on sleep correlated with hangover but did not mediate the effects on performance. No effect of beverage congeners was found except on hangover severity, with people feeling worse after bourbon.

While drinking lots of bourbon causes a worse hangover than drinking lots of vodka, impairment in people's next-day task performance is about the same for both drinks. Therefore, after a night of heavy drinking it is better to avoid driving even the next morning.