Even if the meds are something like Pepcid or Norco, if those abruptly stop working, that's going to be a Thing. There will be tests, and attempts with new meds, or the doctor will just stop prescribing them.

Also, depending on what kind of meds they are, the doctor might be giving regular drug tests. And while they do look for other drugs, the main goal of those tests is to look for the prescribed drug, and thus to be sure the patient is taking them (and not selling them). Whoever the person prescribed the meds is, they could have faced real consequences.

I admit my perspective is skewed (finding out a "friend" was knowingly causing me pain is more than I could stand.