Caffeine addiction is such a downer that
regular coffee drinkers may get no real pick-me-up from their morning
cup, according to a study by British scientists.

Bristol University
researchers found that drinkers develop a tolerance to both the
anxiety-producing and the stimulating effects of caffeine, meaning that
it only brings them back to baseline levels of alertness, not above

"Although frequent consumers feel
alerted by caffeine, especially by their morning tea, coffee, or other
caffeine-containing drink, evidence suggests that this is actually
merely the reversal of the fatiguing effects of acute caffeine
withdrawal," wrote the scientists, led by Peter Rogers of Bristol's
department of experimental psychology.

team asked 379 adults — half of them non/low caffeine consumers and the
other half medium/high caffeine consumers — to give up caffeine for 16
hours, and then gave them either caffeine or a dummy pill known as a

Participants rated their levels
of anxiety, alertness and headache. The medium/high caffeine consumers
who got the placebo reported a decrease in alertness and increased
headache, neither of which were reported by those who received caffeine.

measurements showed that their post-caffeine levels of alertness were
actually no higher than the non/low consumers who received a placebo,
suggesting caffeine only brings coffee drinkers back up to "normal."

The researchers also found that people who have a genetic predisposition to anxiety do not tend to avoid coffee.

In fact, people in the study
with a gene variant associated with anxiety tended to consume slightly
larger amounts of coffee than those without it, Rogers wrote in a study
in the Neuropsychopharmacology journal, published by Nature.

This suggests that a mild increase in anxiety "may be a part of the pleasant buzz caused by caffeine," he said.