Collecting this in one place because it comes up every few weeks and the answer is always assembled from scratch. It is about semaglutide, and it is deliberately narrow — everything I am not confident about is marked as such.
What is actually established
The dose-response is real but shallow at the top. Across STEP 1 and STEP 4 the gap between 1.7mg and 2.4mg is a couple of percentage points of body weight on average, and the average is carrying a wide spread — plenty of people at 1.7mg sit above the 2.4mg mean. If a dose is working and tolerable, "working" is the relevant variable, not "maximal".
The condition it depends on
"tolerable" needs defining. A dose you tolerate by eating almost nothing is not tolerated, it is being paid for somewhere else — usually in lean mass, sometimes in adherence three months later.
The practical version
Worth knowing that the injection site changes very little. Abdomen, thigh and upper arm are bioequivalent for semaglutide, so a site change is not a plausible explanation for a bad week.
What I am not sure about
What I am trying to establish is how much of the between-person variation is pharmacokinetic and how much is just adherence measured badly. Happy to be told the question itself is wrong.
— adam_van · corrections welcome and will be edited into this post with credit