Putting this up for argument rather than for agreement. I have read it twice and I am still not certain what it supports.
The GIP arm is doing real work rather than padding the label. GIP receptor agonism appears to improve adipose insulin sensitivity and lipid handling, and — counter-intuitively — GIP signalling in the CNS reduces nausea rather than adding to it, which is why tolerability at high total agonism is better than the GLP-1-only comparison would predict. SURPASS-2 is the cleanest head-to-head: tirzepatide beat semaglutide 1mg at every dose tier.
Where I think it is weakest: the subgroup findings are the part I trust least — with enough subgroups something is always significant, and these were not all pre-registered.
So the question, as narrowly as I can put it: how much of the tirzepatide advantage is the GIP component and how much is simply that the dose ladder goes higher in receptor-occupancy terms. Not looking for reassurance. Looking for the part I have got wrong.
SarahChen_PharmD said:The GIP arm is doing real work rather than padding the label.
That is correct as far as it goes, and here is where it stops going. Steady state is faster than people expect: half-life about five days, so you are at plateau in roughly three to four weeks rather than five. That matters when you are deciding whether a dose step has finished expressing itself.
SarahChen_PharmD said:The GIP arm is doing real work rather than padding the label.
I read this differently from SarahChen_PharmD, on substance rather than tone. The "tirzepatide is simply better" summary irritates me. It is better on mean weight loss, and the cardiovascular outcome evidence is far thinner than semaglutide's. If the reason for treating is cardiovascular risk rather than weight, the evidence base points the other way.
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Browse GL BiochemAnswering the narrow version, because the broad one does not have a single answer. SURMOUNT-1 landed around 20.9% mean weight loss at 15mg over 72 weeks, against roughly 15% for semaglutide 2.4mg in STEP 1. Different trials, different populations, so the comparison is indicative rather than decisive — but SURPASS-2 was a genuine head-to-head and it pointed the same way.
MikeFit_NJ said:Steady state is faster than people expect: half-life about five days, so you are at plateau in roughly three to four weeks rather than five.
Agreed, and the adaptation point cuts both ways: tachyphylaxis to gastric emptying is why tolerability improves, and it is also why people who were relying on physical fullness feel the effect fade while the appetite effect is still working.