This is the version of the explanation I wish somebody had given me, written down before I forget what confused me. It is about tirzepatide, and it is deliberately narrow — everything I am not confident about is marked as such.
What is actually established
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.
The condition it depends on
The caveat that the head-to-head used semaglutide 1mg, not 2.4mg. It is still the best direct evidence available, but it is not the comparison most people think they are citing.
The practical version
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 not sure about
What would genuinely help is knowing 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.EndoIndy 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.
Dr.EndoIndy has the substance of this right. The condition it depends on is worth stating. 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.
Dr.EndoIndy 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.
Pushing back on Dr.EndoIndy here. 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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Shop Reference StandardsShort answer first, then the reasoning. 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.
labquiet_amy said:SURMOUNT-1 landed around 20.9% mean weight loss at 15mg over 72 weeks, against roughly 15% for semaglutide 2.4mg in STEP 1.
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.