"Ok, here is what is going to happen when vaping caffeine. Caffeine sublimes from solid to gas. It will deposit caffeine solid into your throat, nose and sinuses. Yes, it would work to get caffeine, BUT IT WOULD SUCK!! It would burn your nose a lot, possibly making it bleed, and I have no idea what caffeine in the lungs would do. It is not the same kind of stimulant as nicotine. Caffeine works by blocking cyclic AMP, forcing the body to start using up the ATP energy system. It mimics adenosine monophosphate (AMP) primarily, not like nicotine that stimulates the brain directly. Mucus membrane absorption is far less effective, because of its structure, than digestion in the gut. "
Definitely not a good idea!