Perhaps in the form of a nicotine gum. He already has an insanely severe problem with habit forming substances and with getting/keeping employment. He doesn't need to add actual tobacco into the mix. There are also a lot of fat smokers out there. I agree that some meth may be just what the doctor ordered.
methamphetamine does exist as part of a few still-existing Rx drugs. see
Desoxyn, intended for ADD/ADHD cases (Bushie probably could meet the diagnostic criteria, with his genetically inherited clock-checking and whatnot)