Using coffee for a pick-me-up may be pointless if you drink it all the time, researchers believe.
Experts say they have discovered that people who drink a lot of caffeine develop a tolerance to its stimulatory effects.
While caffeine can give people a buzz, raising alertness, the effect only works in those unused to the drink, they tell Neuropsychpharmacology journal. They base their assumptions on the results of an experiment that they carried out on 379 volunteers.Cold turkey
To put coffee to the test, the scientists from the UK and Germany asked all of the trial participants to abstain from the beverage for 16 hours.
Half of these were medium to heavy coffee drinkers who consumed at least one and up to six cups a day, and half were non or low drinkers. Next, they gave half of the participants a 100mg espresso-sized dose of caffeine, and the other half a placebo shot containing no caffeine.
The medium/high caffeine consumers who received placebo reported a decrease in alertness and an increase in headache, neither of which were reported by those who received caffeine. However, their post-caffeine levels of alertness were no higher than the non/low consumers who received a placebo.