The US military has been doing studies on caffeine for ages. There's a huge body of research confirming effects like this -- as a rule of thumb, caffeine can im

The US military has been doing studies on caffeine for ages. There's a huge body of research confirming effects like this -- as a rule of thumb, caffeine can improve many simple motor functions under sleep deprivation and can't do much for most higher cognitive functions. Other factors (e.g., typical dosage or how recently you slept) impact the details substantially.