I never used to chew gum, but caffeine doesn't work for me with any consistency anymore. Sometimes it works, but other times I can drink enough to make myself jittery and yet fall asleep in those dreadful post-lunch, midafternoon doldrums. I have never yet fallen asleep while my jaw's moving though, whether during meetings, talks, or coding at my desk.
The only major downside I've found so far is that if I chew for too long, my gums start to feel itchy, like I need to chew something harder.
This is probably the most useful thing that I will ever post here.
Incidentally, if you do this, please try to chew with your mouth closed. I hate, hate, hate the sound of human beings chewing with their mouths open, and I would not want to inflict it on anyone.