Alcohol is all very well, but there is another substance which can cause a great deal of trouble for pilots when drunk to excess before flying.
I think that we are overdue for some official studies and HSE guidelines on its use as well, since it can to my certain knowledge lead to extreme pilot discomfort and to increasing pressure (literally so in fact) to make rushed decisions, particularly with regard to landing.
I am referring of course to that enemy of the long-distance pilot: coffee.