Yes, of course it is! And so what?
Am now on my third cup and this is my second post responding to you in as many minutes (need I say more?)...... personally, I believe the third cup of coffee is like the third martini.... it should be consumed with extreme caution.
I blame my own addiction on my parents; my father, whom I've spoken of at length would wake me up two hours before dawn to go flying.... on the way to the airport he would buy me two cups of coffee (this is from about the age of FIVE), one to wake me up, I think, so I would be able to focus on the fact that I held his life in my feet, as it were, and could stand on the brakes of his CHamp while I held the stick back..... and he pulled the prop through.... nuts, yes, and sometimes I shudder to think he did that.... but, whatever... the second cup was just because I was, HELLO, addicted.... of course, we had very short legs to our trips due to excessive bathroom breaks.
... and then my mother, who was so tired of me oversleeping for school, put a coffee pot and a radio on a timer next to my bed when I was 14, so I woke up to coffee and rock n roll at whatever ungodly hour she deemed my wake up time.
It's vicious, but better than a shot of Jack Daniels for wakeup call.... so it could be worse.
There's nothing more beautiful than flying into the dawn.