Scientists have divided the 16 consumers of caffeine in two groups. One group was maintained for three weeks with about 400 milligrams of caffeine per day (equivalent to two cups of strong coffee a day), and others spent three weeks taking a placebo. Then they changed groups. Passing either the placebo to the caffeine caused strong changes in blood flow to the brain, and those who switched to placebo had headaches, decreases energy and attention disorders.
It is important that there were no significant differences between the two periods. Whether the person consume caffeine or placebo constantly, most effects are physiological, and fatigue and alertness were identical. The only apparent benefit in consuming caffeine was that it prevented the withdrawal symptoms.
The lead author, Stacey Sigmon, a research professor of psychiatry at the University of Vermont, suggests that regular users of caffeine can be fooled. “the tolerance develops,” she said, “and you do not get any benefit.”
Dr. Sigmon is a coffee drinker, and has no plans to stop.