I've found that too. Increased alertness without the anxiety and jitters that equal amounts of coffee might bring. Also, one reason tea is said to be so popular with Buddhist monks is that it helps them concentrate and stay focused during long sessions of study and meditation.

These properties are often attributed to tea supplying theanine without too much caffeine. Theanine is also said to reduce the response to stress in which the body's sympathetic nervous system goes into overdrive.

Yes, green tea boosts your metabolism, but just a little. It makes you hungry quicker, and can cause nausea if you drink several cups on an empty stomach without eating anything.

But in this respect, the raw puer tea is much better - definitely not recommend to drink it without eating something before.

It can also make you more aware and vigilant - for me, when I was preparing for my accounting and finance qualification exams, long study sessions were supported by puer tea.