[Swizec]

The coolest thing about caffeine is that it does actually help with mental agility and various cognitive tasks. But surprisingly few cognitive tasks. It actually only increases your working memory and positively influences your ability to concentrate on a task. That's it.

More interestingly still, it doesn't have any cognitive effects at all unless you're sleep deprived. It also doesn't have any cognitive effects in the morning. So that coffee people drink in the morning to wake up, that's just a placebo (unless they slept less than 6 hours, then it helps a bit).

But it does have a bunch of physical effects. Like increased blood flow to the brain, which helps with various things regardless of the fact that blocking adenosine receptors is doing jack shit. It also increases your stamina and physical strength. Which can be useful. Also why a lot of sports bars and most flu medicine contain a bunch of caffeine.

I write about this a lot in my book about Why programmers work at night: https://leanpub.com/nightowls (shameless plug :))

[cma]

Flu medicine has caffeine because often people unknowing go through caffeine withdrawal unknowingly while they have the flu. Excedrin has it because people with headaches often just hadn't had their fix recently enough. Headaches are one of the major things a day or two after stopping.

[unmei]

Caffeine also potentiates the effects of OTC painkillers

http://www.ncbi.nlm.nih.gov/pubmed/2012456

[nbouscal]

You're underselling working memory. Working memory is essential for almost everything productive that you do.

[reneherse]

And a few of the drawbacks of caffeine:

• It causes peristalsis of the intestines, resulting in what might be called "premature" defecation. I have a hunch this reduces nutrient absorption in the small intestine.

• The "pick me up" you receive when drinking your morning joe is actually just the elimination of your body's withdrawal symptoms through reintroduction of the stimulant. It raises you back to "normal".

• Depending on whether your body metabolizes caffeine quickly or slowly, even a small/moderate dose early in the day may disrupt your sleep cycle, perpetuating insomnia.