We live in strange times when if someone doesn't drink, we think they are an alcoholic.
Seriously, just say "no, thanks." If they push it, look them straight in the eyes and repeat, "no."
I spent far too much time in the previous sober periods trying to come up with good excuses, usually linked to so medical condition/test or upcoming surgery along with a health goal I had set and a temporary break. It all got too complicated. Straightforward and unapologetic is the best bet.