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Feeling sleepy? Don't have a high sugar, low caffeine drink -- it could make things worse

Research news from Human Psychopharmacology: Clinical and Experimental


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, nil carbohydrate drink.

This was the finding of research performed at the University of Loughborough and published in this month's Human Psychopharmacology: Clinical and Experimental.

Ten healthy adults had volunteered to restrict their sleep to 5 hours on the day before participating in the trial. An hour after eating a light lunch they were given either an energy drink (42g sugar + 30mg caffeine) or an identically tasting zero-sugar drink. They then performed a monotonous 90-minute test during the afternoon 'dip' that assessed their sleepiness and ability to concentrate.

For the first 30 minutes there was no difference in the reaction times or error rates, but 50 minutes after consuming the drinks, the performance of those who had had the energy drink started to slip, and they became significantly sleepier.

Other researched work shows that high energy drinks that contain caffeine will boost concentration.(1)

"A 'sugar rush' is not very effective in combating sleepiness - so avoid soft drinks that contain lots of sugar but little or no caffeine," explains Professor Jim Horne, who runs the Sleep Research Centre at the University of Loughborough. "A much better way to combat sleepiness is to have a drink that contains more useful amounts of caffeine and combine this with a short nap".


Notes to Editors

  • Physiology & Behavior, 2002, 75: 331-335.

  • Full citation: C. Anderson & J.A. Home. A high sugar content, low caffeine drink does not alleviate sleepiness but may worsen it. Hum Psychopharmacol Clin Exp 2006; 21: 1-5

  • Human Psychopharmacology: Clinical and Experimental provides a forum for the evaluation of clinical and experimental research on both new and established psychotropic medicines. Experimental studies of other centrally active drugs, including herbal products, in clinical, social and psychological contexts, as well as clinical/scientific papers on drugs of abuse and drug dependency are also be considered. While the primary purpose of the journal is to publish the results of clinical research, the results of animal studies relevant to human psychopharmacology are welcome. The journal's co-editors are Professor Stephen Curran of the University of Huddersfield, UK and Professor C. Lindsay DeVane of the Medical University of South Carolina, Charlestown, USA. Human Psychoparmacology can be accessed at:

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