The 2.5 mg starting dose is not a therapeutic dose — why that matters posts 91–120

Building on post #104 rather than restating it.

What I want from this 2.5 mg starting dose thread is the list of things that would need to be true for the claim to hold. If we can write that list, we can check it.

Research-use-only tirzepatide is not approved for human use and is not made to pharmaceutical standards. Anyone discussing it here is describing what they did, not recommending it.

The thing about 2.5 mg starting dose that took me longest to accept is that a plausible mechanism is not evidence of an effect. It is a reason to look, not a result.

Having read the whole 2.5 mg starting dose thread before replying: the question in the first post has not actually been answered yet, and three of us have answered a nearby one instead.

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.

Coming back to post #106, because the follow-up matters more than the original answer.

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.

Coming back to post #109, because the follow-up matters more than the original answer.

Categorical response thresholds — the proportion reaching ten, fifteen or twenty per cent reduction — are more persuasive and less informative than the mean. They depend entirely on where the threshold was drawn.

Post #109 is right about the mechanism and I think understates the practical bit.

I would rather this thread reach "we do not know" about 2.5 mg starting dose than reach a confident answer that nobody can support when asked.

On 2.5 mg starting dose, the part that usually goes wrong is that the question is asked as though it has one answer. It has a range, and the width of the range is the interesting bit.

If you can post the two or three numbers you are working from, several people here will check the arithmetic rather than argue about the conclusion.

Research-use-only tirzepatide is not approved for human use and is not made to pharmaceutical standards. Anyone discussing it here is describing what they did, not recommending it.

That is what the documentation says. What happens in practice is usually close.

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.

Seconded. It reads as careful rather than confident, which is the right register.

Post #113 and I disagree about the size of the effect, not about the direction.

I changed my mind about 2.5 mg starting dose after someone here asked me for the source and I could not produce one. That is worth saying out loud because it is the ordinary way it happens.

Two claims get bundled together under 2.5 mg starting dose 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.

Where I part company with post #117, and it is a narrow parting.

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.

The confident version of this sentence would be wrong, so here is the hedged one.

I keep a log for 2.5 mg starting dose specifically because my memory of it turned out to be systematically wrong in one direction. Six weeks of notes cost nothing and settled it.