Dr. Donald Hensrud, the director of the Mayo Clinic’s Healthy Living Program describes them as ‘next in line on the spectrum’ after ‘your five-Hour Energy drinks’, indicating caffeine vaping is more of a substitute for energy drinks than it is for smoking. The vaporisers do work exactly like an e-cigarette though; they use heat to convert the ingredients into vapour, which is then inhaled through the lungs. Caffeine vapers release 2 milligrams of caffeine per inhalation, which is less than your average cup of Americano, but all those inhalations add up to a considerable caffeine hit.