So right. Cover Your A$$So I'm going to take it would be a reasonable assumption that your wife attend your doctor's appointment and have him acknowledge that it's possible or likely that her blood tests can fail due to the second hand exposure to the prescribed medication that her husband consumes.
There are always exceptions to the rules and burden of proof is always on the employer. In a safety sensitive position (physically) well they probably have some ground to stand on. If not it all the better for you.
The forst thing I would do is start documenting this. Because you never know when you will need it.
A simple email stating in regards to our conversation regarding your concern over possible drug use. Please accept this doctor's affidavit that that should/hopefully state due to medical requirements of her spouse it is a reasonable expectation that drug test may come back positive.
Send a read receipt with it.
Now you are starting to put some ground under your feet for future harassment, intimidation or human rights violations such as discrimination.
Usually once things start to end up in writing employers, senior authorities start to have that little light bulb turn from the usual dim to a smal flicker of brightness for a second and they realize they need to be careful of thier actions. The ones with poor E.C. (electrical conductivity) <----- se what I did there? Can be a lotto ticket or don't last once a superior catches on.
This is not advice... its strictly a hypothetical scenario that was babbled in the web of lies by a random plaid wearing, moose riding guy from that iceberg called Merica's hat