Energy drinks that contain sugar and caffeine are a popular remedy for drowsiness, but new research shows that some such drinks may actually make a tired person feel worse. An hour after consuming a high sugar, low caffeine drink you will tend to have slower reactions and experience more lapses in concentration than if you had simply drunk a decaffeinated, zero-carbohydrate drink says a study performed at the University of Loughborough in Leicestershire, England, and published in the journal Human Psychopharmacology: Clinical and Experimental.

In the study, 10 healthy adults volunteered to sleep only 5 hours on the night before the trial. An hour after eating a light lunch they consumed either an energy drink containing 42 grams or sugar and 30 milligrams of caffeine, or a sugar-free drink. They were then tested with the Psychomotor Vigilance Test, a monotonous 90-minute test that can assess one’s ability to concentrate and degree of sleepiness.

There was no difference in reaction times or error rates between those who had the energy drink and those who had the sugar-free drink for the first 30 minutes of the trial. However, 50 minutes after consuming the drinks, the performance of those who had had the energy drink began to decline and they became much sleepier.

"A ‘sugar rush’ is not very effective in combating sleepiness," said Jim A. Home, one of the authors of the study. Instead Home recommends a short nap and a high-caffeine beverage to combat drowsiness.