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ForumsPublic SquareComparative pharmacokinetics: semaglutide vs tirzepatide vs retatrutide Page 2

Comparative pharmacokinetics: semaglutide vs tirzepatide vs retatrutide

SarahChen_PharmD Sun, Jun 7, 2026 at 9:43 PM 6 replies 206 viewsPage 2 of 2
FDA_TrackerJim
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Jun 7, 2026 at 11:29 PM#6

Adding the numbers, since they settle part of this. 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.

Ask again with the specifics and you will get a better answer than this one.

Last edited: Jun 8, 2026 at 2:29 AM
49 19Dr.Martinez, mike_mod, SarahChen_PharmD and 46 others
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zoe_NC
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Jun 8, 2026 at 12:10 AM#7

Following on from PeptideChemSF — and this may be the naive question:

What the dose-response curve actually looks like above 1.7mg, because the trial means hide how few people account for the extra loss?

48 18FranDenver, Dr.BariatricHTX, LindaRN_retired and 45 others
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Dr.RheumBOS
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Jun 8, 2026 at 12:51 AM#8
FDA_TrackerJim said:
Worth knowing that the injection site changes very little.

There is a second half to this that has not been said yet. 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".

Last edited: Jun 8, 2026 at 6:51 AM
47 17cory_ATX, lori_vegas, Dr.PulmRoch and 44 others
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SarahChen_PharmD
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Jun 8, 2026 at 1:32 AM#9

Closing the loop on my own question.

Update — tachyphylaxis to the gastric effect, persistence of the appetite effect. Two curves, and I had been watching the wrong one.

46 16TinaHashiRN, robert_kc, dan_philly and 43 others
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VanRx_Mike
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Jun 8, 2026 at 4:51 AM#10
Dr.RheumBOS 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.

50 0mike_mod, SarahChen_PharmD, sarah.morrison and 47 others
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