Since this sounds like an extremely careless-on-purpose-passive-aggressive behavior and unacceptable response in return I would get a BIG bottle of Bitter YUCK (yes that's a brand) and a roomba would be good too. I'd either toss in the garbage or spray bitter yuck on the wayward pill & maybe put it back in the bottle. Yes I've lived with PA people before.
It sucks being in that position.

That aside thought vicodin was pulled from the market, not that there aren't equally toxic to animals pills out there, doesn't matter what it is really, could be a vitamin. Another thing you have to worry about is any xylitol added to anything these days.

I'm a "fuck with my animals on purpose at your peril all bets are off after that" kind of person. Yes people make mistakes, me included, but belligerent is a choice. FTS.

Go to Target or the Dollar store and get a black plastic oil change pan or a plastic lunch tray and confine pills to that.

You could take the pill bottles away and dispense them when it's time to take them if they're willing to do that.
Stand there and make sure they swallow them too.