That really has little to do with what I mention. You cannot prevent someone from drinking as we all know the body requires fluid to function. Whilst drinks loaded with caffeine won't have the same effect water does it is still fluid intake.
If someone was off to the coffee machine every 10mins to get a caffeine hit then yes I would expect someone to say something to them as their addiction is affecting there work output.
Yeah, and if they had a device that allowed them to drink coffee at their desk instead of taking any breaks at all, would you advocate it?