It's a great point. Propylene glycol sensitivity is uncommon but real. If someone was having low-grade injection site reactions on Ozempic (which contains PG) and then switched to Wegovy (which doesn't), they might actually feel BETTER at the injection site despite the higher dose. Conversely, if someone has sensitivity to the higher NaCl concentration, Wegovy could sting more.
This is one of those areas where the "it's the same drug" oversimplification really fails patients. Biosimilars and reformulations are NOT always clinically interchangeable in terms of patient experience, even when bioequivalence is demonstrated at the population level.