OK, thanks all for the answers. Red Bull helps with my wife's cluster headaches, strong tea or coffee does hot, hence the question. The exact mechanism of how is not well understood, so let's not turn this into a thread on whether it works or not :-)
We'll try and hunt some down at T5 air side.
ThatT1Feeling - no offence taken but can't really refuse to sit next to my wife, can I :-) I don't drink the stuff (or any caffeine) so will be asleep!