Methylxanthine

Caffeine is the world's most widely used psychoactive compound, a methylxanthine that works by blocking adenosine receptors. At low to moderate doses it reliably improves alertness, vigilance, attention and reaction time, with weaker and less consistent effects on memory and higher-order judgment. It is the reference point every other stimulant on this wiki gets compared to.

Paraxanthine (1,7-dimethylxanthine) is what most caffeine turns into in the body: about 80% of a caffeine dose is converted to it. Like caffeine it blocks adenosine receptors, and at 4 mg/kg it raised diastolic blood pressure and adrenaline in people about as much as the same dose of caffeine. It is now sold on its own as a supplement. Small crossover trials funded by the ingredient's sponsor report better scores on some attention, memory and reaction-time tests after 50 to 200 mg, though their main statistical tests were not significant.