Revisiting: Why tirzepatide titration schedules have more steps than semaglutide's posts 31–60

Reading back through, this was answered upthread and I missed it. My fault.

This follows post #44 rather than contradicting it.

The question underneath tirzepatide titration schedules is usually "how would I tell?" rather than "what is true?", and that one has a method attached to it.

Write down what you would expect to see under each hypothesis before you collect anything. If they predict the same observation, collecting it will not help.

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.

On purity: the trailing-edge features people report on tirzepatide chromatograms are frequently deamidation products, which elute close to the main peak and are easy to integrate into it. That is a method question rather than a quality question.

That holds under the stated conditions and I have stated them.

Agreed on tirzepatide titration schedules, with one qualification that I think matters. The reasoning holds for the case as described. Change the starting assumption and it does not, and the starting assumption is the part nobody states.

The titration schedule has more steps than semaglutide's, which reflects the finer gradation used in the clinical programme rather than a pharmacological requirement for smaller steps.

That has been true for the cases I have seen and I have not seen many.

Post #50 answers the question as asked. The question underneath it is different.

Comparisons between the tirzepatide and semaglutide programmes across trials rather than within one are weak. Different populations, different durations, different baseline characteristics; the only fair comparison is a head-to-head one.

I read post #48 twice before replying, because I had assumed the opposite.

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.

That is where I would start, not where I would stop.

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.

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.

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.

Second this, and I would have said it less carefully.

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.

Happy to be the one who is wrong here if it settles the question.

Storage and stability: published data on licensed tirzepatide formulations exists and is worth reading directly rather than through summarised claims. Reconstituted preparations in different diluents have not been studied and extrapolation from the licensed formulation is the best you can do.

Adding the caveat now so it does not have to be extracted later.

The documentation on tirzepatide titration schedules is better than this thread and I say that as someone who has posted in the thread.

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.