A person who possesses a prescription drug may legally possess a firearm provided federal law recognizes the drug as having a medicinal purpose.
I don't think that's all that is required...
18 USC 922
(g) It shall be unlawful for any person—
(3) who is an unlawful user of or addicted to any controlled substance (as defined in section 102 of the Controlled Substances Act (21 U.S.C. 802));
to ship or transport in interstate or foreign commerce, or possess in or affecting commerce
Using a drug outside of the instructions on the prescription is unlawful, as is "doctor shopping" to get multiple pain prescriptions, for example. Rush Limbaugh was addicted to a controlled substance with a recognized medical purpose, making it unlawful for him to possess guns (that affect interstate commerce, of course
At what point should we talk about the merits of that law, or the constitutional authority it is founded upon?