Well, unfortunately, drug-testing is common in such a situation. And there's actually a good reason for it. A person might be self-medicating with other pills (or, when it comes to things like bipolar and schizophrenia, a certain illicit powdery substance), and this could affect the medications that the person is being - or might be - prescribed. Alternatively, consider someone who is receiving meds at a discount because either their insurance or the taxpayers are buying them. Some of these people will get their prescriptions filled and then turn around and sell the meds instead of consuming them.
The above are general things, of course, and I am certainly NOT implying that your wife falls into either category.
IF your wife is refusing ALL prescription meds from her doctors, then they have no real reason to ask for a drug test.
The unfortunate thing isn't that people who receive medicines such as antipsychotics, opiates, et cetera are subject to drug-testing - it's that cannabis, when the markers indicating recent(+/-) use are present, is treated as an illicit substance. I know that it can affect the effects of certain medications, but so can a huge list of perfectly legal (everywhere) substances. It's not a bad thing, lol, it's just a thing. So is chocolate. Or caffeine from coffee, or nicotine from cigarettes (and these two can also affect one's meds, so...).
BtW, has your wife ever been prescribed Geodon? A friend of mine (schizophrenia, bipolar, and other issues) was on that for a while. And it helped... for a while. When it was helping, the only real side-effect seemed to be a tendency to sleep a lot more than normal.
