On the mechanism question specifically: the honest position is that GIP agonism plausibly contributes and that the trial design cannot separate its contribution from simply achieving greater receptor engagement overall.
Does dual agonism explain the effect size, or is it dose? I have a specific reason for asking rather than idle curiosity, and the context is below.
A question about dual agonism that I think has a definite answer, unlike most of what I ask here.
I have the reasoning below and I am fairly confident about the direction. I am not confident about the size, and the size is what the decision turns on.
Narrowing the opening post, because the general version has more than one answer.
The apnoea-hypopnoea index used in SURMOUNT-OSA is an objective measurement rather than a symptom scale, which is why that trial carries more weight than its size suggests. Two parallel trials with and without positive airway pressure addressed the obvious confounder directly.
I am confident about the direction and much less about the magnitude.
Checked the dual agonism claim against the primary source this morning. It survives, with a narrower scope than the version quoted here. Posting the narrower scope.
The GIP component: GIP receptor agonism is thought to amplify the GLP-1 effect on satiety and energy expenditure, but how much of tirzepatide's effect is that and how much is simply achieving higher receptor occupancy remains genuinely open. The mechanistic literature is active.
Answering the question post #5 raises rather than the one it answers.
SURMOUNT-4's randomised withdrawal design is the strongest available evidence about what happens on stopping. It says nothing about a lower maintenance dose, because the comparison was continue versus placebo rather than continue versus less.
Genuinely open to being wrong about this one.
SURMOUNT-4 used a randomised withdrawal design: everyone titrated, then those on maintenance were randomised to continue or placebo. Continuation maintained effect; withdrawal was followed by regain. The finding is robust but it says nothing about a lower effective maintenance dose, because that was not studied.
Flagging that the sources on this are thinner than the confidence in the thread suggests.
On the mechanism question specifically: the honest position is that GIP agonism plausibly contributes and that the trial design cannot separate its contribution from simply achieving greater receptor engagement overall.
Confirming post #9 from a second method, which matters more than confirming it from a second person.
SURPASS-2's comparator choice is the criticism that survives. Semaglutide 1.0 mg was the licensed diabetes dose at the time and it was not the highest dose available in the class, so the trial answers a narrower question than the headline implies.
Where I would look next, rather than where I would stop.
The published pharmacokinetics show dose proportionality across the studied range, which means dose arithmetic behaves the way you would naively expect. That is not true of every compound and it is worth knowing which ones it is true of.
Worth one more sentence than it usually gets.
SURPASS-2 compared tirzepatide with semaglutide 1.0 mg, the licensed diabetes dose at that time. It did not compare with semaglutide 2.4 mg, the highest approved dose. That is the central and legitimate criticism of the head-to-head evidence and it is worth remembering when people quote the trial.
Post #10 is the version of this I will quote in future. One addition.
Two claims get bundled together under dual agonism and they need separating. The descriptive one — this is what was observed — is usually well supported. The causal one — this is why — usually is not.
Almost every disagreement in threads like this one dissolves once you say which of the two you are making.
Nothing to add on the substance. Thank you for taking the question at face value.
Dual agonism versus dose: how much of tirzepatide's effect is the GIP component and how much is simply achieving higher receptor engagement? The honest answer is that the question is not settled. Some of the effect is surely the GIP component, but the trial design does not decompose it.
On reflection I would soften that slightly.
Building on post #14 rather than restating it.
The 2.5 mg starting dose is not a therapeutic dose in the sense that weight loss is minimal at that dose. It is a tolerance-testing dose. Confusing the purpose of a starting dose with the purpose of a maintenance dose leads to false conclusions about efficacy.
Post #16 put the caveat in the right place and I want to underline it.
The most useful thing anyone has posted about dual agonism in this category was a table of what had been measured and by whom. That is what I would want again.
This follows post #18 rather than contradicting it.
What I would tell a new member reading about dual agonism for the first time: the confident posts are not the reliable ones, and the reliable ones are longer.
SURMOUNT-1 reported weight reduction of a magnitude that was the largest for a pharmacological intervention at that time of publication. It also reported a clear dose response across three doses. The categorical thresholds (people reaching 10%, 15%, 20% loss) got the most attention but read less informatively than the mean weight change.
Not disagreeing with anyone above, just adding the bit I keep having to look up.
Reporting rather than recommending, on dual agonism. What happened is above. Whether it should have is a different question and not one I am qualified to answer.
Titration schedules for tirzepatide have more dose steps than semaglutide partly because the compound is more potent and partly because the clinical programme used a finer gradation. That does not mean you cannot escalate on a coarser schedule if that suits you — the published schedule is not a lower bound.
The arithmetic in post #21 is right; the assumption feeding it is the part to check.
The dual agonism is not a marketing framing — GIP receptor and GLP-1 receptor engagement are both demonstrable. What is genuinely unresolved is how much of the clinical effect the GIP limb contributes, because no trial decomposes it.
I have seen it go both ways, which is why I hedge.
Right — I had this wrong and I am glad to have read it before it mattered.
Since dual agonism keeps coming up, it should probably be a maintained page rather than a recurring thread. I am happy to draft it if someone with more direct experience will review it.
Post #26 describes the usual case. This is about the unusual one.
SURPASS-2's comparator choice is the criticism that survives. Semaglutide 1.0 mg was the licensed diabetes dose at the time and it was not the highest dose available in the class, so the trial answers a narrower question than the headline implies.
Someone will know this better than I do and I hope they say so.
Adding the measurement that post #26 says would settle it.
SURMOUNT-1 reported weight reduction of a magnitude that was the largest for a pharmacological intervention at that time of publication. It also reported a clear dose response across three doses. The categorical thresholds (people reaching 10%, 15%, 20% loss) got the most attention but read less informatively than the mean weight change.
That is all the detail I have. Someone else will have more.
Coming back to post #26, because the follow-up matters more than the original answer.
SURMOUNT-4's randomised withdrawal design is the strongest available evidence about what happens on stopping. It says nothing about a lower maintenance dose, because the comparison was continue versus placebo rather than continue versus less.
Second-hand, so weight it accordingly.
Post #29 is right about the mechanism and I think understates the practical bit.
Titration schedules for tirzepatide have more dose steps than semaglutide partly because the compound is more potent and partly because the clinical programme used a finer gradation. That does not mean you cannot escalate on a coarser schedule if that suits you — the published schedule is not a lower bound.
Scoping that to what I have actually seen rather than what I have read.