One concrete data point for the thread. 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.

One thing that is still open after paige_pharma’s answer:

How much of the between-person variation is pharmacokinetic and how much is just adherence measured badly?

lisa_labSD said:

Worth knowing that the injection site changes very little.

There is a second half to this that has not been said yet. Steady state is the thing most people miss. The terminal half-life is about a week, so every dose step takes four to five weeks to fully express itself. Judging a step at day ten is judging the ascent, not the plateau, and it is the single commonest reason people escalate before they needed to.

Closing the loop on my own question.

Following this thread I went back and re-read the extension data properly. The point about trough rather than peak explains the pattern I was seeing on day six, which I had been blaming on the vial.

Dr.KarenChen said:

Steady state is the thing most people miss.

All true, with one condition: that curve is for people who reached the dose on schedule. Anyone who slowed the ladder for tolerability is on a different, flatter curve, and comparing yourself with the published mean will make you feel like a non-responder when you are not.