Are heavy coffee drinkers immune to caffeine?

Scientists from Britain and Germany tested the impact of caffeine versus a placebo on subjects who had abstained from caffeinated beverages for at least 16 hours.

When the researchers gave heavy coffee drinkers the amount of caffeine in a cup of espresso, the subjects were just as alert as non coffee drinkers who received a placebo. The scientists say that shows that heavy coffee drinkers have developed a need for caffeine just to maintain normal levels of alertness.

In addition, the heavy coffee drinkers who received a placebo reported a decrease in alertness, accompanied by headaches.

"Although frequent consumers feel alerted by caffeine, especially after their morning tea, coffee or other caffeine-containing drinks, evidence suggests that this is actually merely the reversal of the fatiguing effects of acute caffeine withdrawal," said Professor Peter Rogers of Bristol University.

This report came from the Neuropsychopharmacology journal.

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