This is the version of the explanation I wish somebody had given me, written down before I forget what confused me. 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
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.
The practical version
For anyone assembling their own picture: Tmax is one to three days, terminal half-life about 165 to 170 hours, steady state at four to five weeks, and subcutaneous bioavailability near 89%. Those four numbers explain most of the questions people ask about timing.
What I am not sure about
What I am after is how much of the between-person variation is pharmacokinetic and how much is just adherence measured badly. Not looking for reassurance. Looking for the part I have got wrong.
chris_chi24 said:The dose-response is real but shallow at the top.
That holds for the injectable. The oral formulation has different absorption behaviour and the dose numbers are not interchangeable, which is worth saying out loud because people quote them as if they were.
chris_chi24 said:The dose-response is real but shallow at the top.
This is where I part company with the consensus forming above. The trial means are being read too generously in this thread. STEP populations were selected, supported, and titrated by protocol, and the real-world curves are consistently a few points worse. That difference is not noise, it is what happens when you remove the study infrastructure.
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View ResultsThis one has a reasonably settled answer, so here it is. 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.
sarah.morrison said:The oral formulation has different absorption behaviour and the dose numbers are not interchangeable, which is worth saying out loud because people…
Agreed, though "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.