Comparative pharmacokinetics: semaglutide vs tirzepatide vs retatrutide — need advice

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

Was that from a primary source or from a summary of one?

WendyG_ATL said:

The dose-response is real but shallow at the top.

Semaglutide structural biology relevant to the pharmacology: semaglutide is a 31-amino acid peptide with 94% homology to native GLP-1(7-36). Three key modifications enable its pharmacokinetic profile:

1. Aib8 substitution: DPP-4 resistance (prevents enzymatic degradation)
2. Arg34 substitution: improved chemical stability
3. C18 fatty diacid at Lys26: albumin binding → long half-life

These three modifications transform a peptide with a 2-minute half-life (native GLP-1) into one with a 168-hour half-life (semaglutide). A masterclass in peptide engineering.

WendyG_ATL said:

The dose-response is real but shallow at the top.

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.

WendyG_ATL said:

The dose-response is real but shallow at the top.

Saving this. It is the first explanation that did not require me to already understand it. Sending this to two other people who asked me the same thing last week.

From the other side of the consultation, briefly. The distinction that resolves most of these threads is between what is true on average and what is true for one person. Both are real; they answer different questions and get quoted as if they were the same one.