I'd perhaps prefer a world in which many drugs were legally sold, which might make this specific issue disappear but even then I'm happy that cigarettes and alcohol, and some other potentially dangerous items are age restricted.
From quickly looking at a few random Theraflu products - they don't seem to contain pseudo. Though asking a random store worker to know that would not be ideal, but a pharmacist should have definitely sold them this medicine without ID.
https://en.wikipedia.org/wiki/Pseudoephedrine#Manufacture_of...
I'd perhaps prefer a world in which many drugs were legally sold, which might make this specific issue disappear but even then I'm happy that cigarettes and alcohol, and some other potentially dangerous items are age restricted.