Ok, I got interested enough that I reached out to my friend who does spacesuit engineering for NASA. She says she’s not aware* of any drugs they take for that purpose while in space. They focus on exercise instead. She speculates this could be an interesting clinical trial.

*Although she adds that what meds the astronauts take wouldn’t really be her area so it’s possible they do and she doesn’t know about it. A different friend in that chat who works in healthcare points out that a lot of anti-osteoporotic meds can cause kidney stones, which would be really bad in space.