Ohh my child is much younger and has only ever stayed at grandparents. Grandparents are part of a WhatsApp group which parents and grandparents write in EVERY time he has any type of medicine. . . I still feel that grandparents would call me if medication was needed for a "new reason".
If staying at a friend's house... mmm. I can't imagine him staying out to be honest - but I know if he did, it would need to be with someone I felt totally comfortable with and trusted. That person would need to know my child incredibly well.
And quite simply, if it were me looking after another child, I'd ring before administering any medication at all.
I can 100% see why there's a breakdown in trust here.
I'd be finding this hard too, playing devil's advocate for a minute, let's say this is someone who you've known a long time, trust explicitly and this person knows your child almost as well as their own child - she felt certain you'd be ok with all of this but has got it wrong, she still needed to tell you!
I'd be looking to make my thoughts known but in a non confrontational way whilst also teaching my child the line "my parents have asked that I always get in touch with them before taking medicines they don't know about."