Fourteen months on tirzepatide, currently 10mg, and I stopped escalating because 10mg is doing the job and 15mg made me feel flat rather than full.
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 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.
Tell me what I have not thought of.
Answering the narrow version, because the broad one does not have a single answer. 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.
I would rather be corrected than agreed with, if it comes to it.
Dr.GastroMayo said:The GIP arm is doing real work rather than padding the label.
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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Browse GL BiochemTomTeleRx said:Fourteen months on tirzepatide, currently 10mg, and I stopped escalating because 10mg is doing the job and 15mg made me feel flat rather than full.
Can confirm the pattern TomTeleRx describes. 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.
I would rather be corrected than agreed with, if it comes to it.
Clinical perspective, offered as context rather than as advice.
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.