While both light caffeine drinkers and heavier caffeine drinkers reported feeling more alert after being given caffeine, there were marked differences in their responses to the placebo.
Those who normally drank few caffeinated beverages didn't notice much of a difference in their level of alertness when given a placebo versus caffeine. Heavier caffeine drinkers given the placebo, however, reported a sharp drop-off in feelings of alertness.
In addition, heavier caffeine consumers given placebo were also much more likely to report having a headache.
"What this study does is provide very strong evidence for the idea that we don't gain a benefit in alertness from consuming caffeine," Rogers said. "Although we feel alert, that's just caffeine bringing us back to our normal state of alertness."
Furthermore, abstaining from caffeine when you're used to having it can cause a "caffeine hangover," Rogers said.
"The nice thing about a caffeine hangover is you can get rid of it quickly by drinking coffee," Rogers noted.
Researchers also looked at caffeine-induced anxiety, a common side effect that's more pronounced in people with a specific variant of the ADORA2A gene, previous research has shown.
In this study, about 20 percent of participants had the ADORA2A variant, Rogers said; other research has put the number of people with the variant as high as one-third.
Researchers found people with the anxiety-producing variant were no less likely to consume coffee than those without the variant and in fact, tended to drink a bit more coffee suggesting that the "anxiety buzz" caused by caffeine isn't necessarily unpleasant, Rogers said.
"They don't seem to particularly mind it, in fact, they might like that anxiety buzz," Roge
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