Pharma companies would already have a caffeine equivalent that would be only slightly different in structure so it would circumvent the law. It would then be sold at exorbitant prices and people would still pay even with the side effect of sometimes you eat someone's face. Of course they would then sell you something else to stop the side effects. You would also have the caffeine purists who would start their own speak easies and organized crime. People "abiding by the law" would start calling the purist, plants, since that is where caffeine is coming from, while the synthetic caffeine users would be called zombies for the obvious face eating reasons. This whole thing would cause even greater divides between already split countries leading to all out war. WWIII plants vs zombies.