There are restrictions for certain locations, based on what I see in Wikipedia https://en.wikipedia.org/wiki/Regulation_of_electronic_cigarettes. You may need to find the laws in your location and see what's required in your location.
As for a standard text or other popup, if your country doesn't require it, you may not need to have a popup (or you may need to determine the user's location based on their IP address and have it popup for certain users only). For standard text, I would look at some of your competitors to see if what they are doing--and consult your attorney or lawyer to make sure your business is compliant (they may provide you with the text to use).