Greentext

The primary effect of caffeine is to block adenosine from getting to the adenosine receptors, and that hormone is generally associated with sleepiness. So it's kind of like caffeine creates an illusion that removes our awareness of sleepiness.

However this also has a cascade of secondary effects on the central nervous system that leead to things like blood pressure changes, improved lung function, increased cortisol and adrenaline levels, etc. Taken together, these things quite objectively generally result in greater feelings of alertness and energy. And anxiety.

As others have noted one case where it can have more of a calming effect is in people with adhd. It should also be noted that overconsumption of caffeine combined with other poor lifestyle choices quickly leads to chronic fatigue system, at which point no amount of additional caffeine is going to continue being helpful and it just becomes a slog of continuing to take it for no other reason than relief from withdrawal symptoms.

One dose a day is all that should be necessary - ideally taken as early as possible. It should also be noted that for most people in industrialized countries, coffee or tea might be their most significant and pretty much only reliable source of polyphenols.

And lastly don't forget the most important reason for drinking caffeinated beverages: the pooping!