Writing this once so I can stop repeating it across threads. It is about tirzepatide, and it is deliberately narrow — everything I am not confident about is marked as such.
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.
The ladder is longer and that is not a neutral detail — six dose steps means six opportunities to stall on the way up, and plenty of people never reach the dose the headline number came from.
Practical numbers: half-life about 5 days, steady state 3 to 4 weeks, ladder 2.5 / 5 / 7.5 / 10 / 12.5 / 15mg, and the maintenance doses with published data behind them are 5, 10 and 15mg.
What I am after is 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. If the honest answer is that nobody knows, that is a useful answer and I would rather have it.
Dr.LeslieOBGYN said:The GIP arm is doing real work rather than padding the label.
No disagreement with Dr.LeslieOBGYN. One condition attached. 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.
Dr.LeslieOBGYN said:The GIP arm is doing real work rather than padding the label.
Filing a mild objection. Mild because I might be wrong; an objection because nobody has addressed the case that does not fit. 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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View ResultsThis one has a reasonably settled answer, so here it is. 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.
FDA_TrackerJim 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.
This is my experience too, for whatever a second data point is worth. I had assumed I was the exception until I read this.