I'm not pregnant (in fact we've completed our family), but I am on strong painkillers and cannot drink, and it made me think of those early weeks in pregnancy when I wished I had a good excuse for not drinking as a didn't want to share my pregnancy news until I was past the 12 weeks.
Anyway, I though this info may be of use to someone. The medicine is naproxen. It's prescribed. It's a strong painkiller/anti-inflammatory/NSAID. You could look up what it's prescribed for and pick something believeable (it can be prescribed for period pain).
Hope this is of some use to someone.