Association of the Anxiogenic and Alerting Effects of Caffeine with ADORA2A and ADORA1 Polymorphisms and Habitual Level of Caffeine Consumption
investigates the effects of coffee consumption among certain groups. They were looking at what coffee does to improve alertness or cause anxiety. The study investigates various phenomena, primarily how certain genes influence coffee’s effects. However, the truly interesting results come when they look at coffee’s effects on those who regularly do / do not use caffeine. From the abstract:
Placebo administration in participants decreased alertness and increased headache. Caffeine did not increase alertness in [none/low caffeine user] participants. With frequent consumption, substantial tolerance develops to the anxiogenic effect of caffeine, even in genetically susceptible individuals, but no net benefit for alertness is gained, as caffeine abstinence reduces alertness and consumption merely returns it to baseline.
That’s right: this study found that caffeine has no value as a performance-enhancing drug. If you are not a regular user of caffeine, caffeine will not make you more alert; in fact it will simply make you anxious. If you are a regular user of caffeine, you’re simply an addict: caffeine will return your alertness to a normal level, but no higher, and only because your alertness decreases when you haven’t used caffeine in a while. On the plus side, regular caffeine users have a high tolerance for the anxiousness-inducing side-effect.
Bottom line: if you think that tea or coffee will make you think sharper, this study disagrees.