I moved from semaglutide to tirzepatide after a long stall and the first eight weeks looked like starting over — which I gather is the usual pattern rather than a lucky one.
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.
This 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.
PharmD_Rodriguez 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.
True, though 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.
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View Resultstammy_FL said:I moved from semaglutide to tirzepatide after a long stall and the first eight weeks looked like starting over — which I gather is the usual pattern…
Can confirm the pattern tammy_FL describes. 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.
From the other side of the consultation, briefly.
Dose-response modeling for tirzepatide: Emax model fitting to the STEP/SURMOUNT dose-finding data shows:
Semaglutide: ED50 ≈ 0.6mg, Emax ≈ -18%, Hill coefficient ≈ 1.3
Tirzepatide: ED50 ≈ 6mg, Emax ≈ -25%, Hill coefficient ≈ 1.5
Clinical implication: most patients achieve >80% of maximal response by the mid-range dose (1.7mg sema, 10mg tirz). Going to the maximum dose provides diminishing returns — possibly not worth the additional side effect burden for some patients. Individualize dosing based on response vs tolerability.
Amazing transformation! Starting at 287 lbs, I'm now at 162 lbs after 18 months on semaglutide 2.4mg/wk. These photos show my progress at months 3, 6, 9, 12, 15, and 18. The body recomposition has been incredible — DEXA shows 23% body fat, down from 42%...