What specific provision in US federal law, if any, prohibits the possession of an uncontrolled prescription drug without a prescription? I've had a lot of trouble finding the answer to this question, since most of the information available relates to controlled substances. I assume this would be found in the Federal Food, Drug, and Cosmetic Act, but have not been able to find it within the U.S. Code section (I haven't read the entire text, but have tried searching extensively). I am completely sure that I am asking about a substance not listed in any schedule of the Controlled Substances Act, e.g. propranolol.
I am also aware that there are provisions about importing these, but I am not asking about that. I am asking about the situation once such a drug is simply found in the possession of someone without a valid prescription for it, with no record of how they obtained it.