Posting this because the summary going around does not say what the paper says, and the difference matters for how people here are using it.
The pharmacokinetics explain nearly every practical question asked here. Albumin binding above 99% slows clearance enough to make weekly dosing possible; a terminal half-life near a week means four to five weeks to steady state and therefore a four-week titration interval; subcutaneous bioavailability around 89% means injection site barely matters. Those three facts answer most timing questions before they are asked.
Where I think it is weakest: the population was selected and supported in ways a real cohort is not, so I would read the effect size as a ceiling rather than an expectation.
The bit I cannot resolve on my own is which effects tachyphylax and which persist, because the answer explains why tolerability improves while the appetite effect keeps working. I would rather have one careful answer than five confident ones.
Figures above are from the primary publication rather than the press summary. If a number here disagrees with one you have, post yours and we will work out which of us is reading a secondary source.
Dr.CardioMD said:The pharmacokinetics explain nearly every practical question asked here.
PK/PD modeling for the pharmacology: understanding the pharmacokinetics helps optimize dosing. Semaglutide:
- Tmax: 24-72 hours post-injection
- T½: ~168 hours (7 days) — enables weekly dosing
- Steady state: reached at 4-5 weeks
- Bioavailability (SubQ): ~89%
- Volume of distribution: ~12.5L (primarily plasma)
The albumin binding (>99%) is the key pharmacological innovation — creating a sustained-release effect from a single injection. Previous GLP-1 agonists (exenatide) required BID dosing due to rapid clearance.
Dr.CardioMD said:The pharmacokinetics explain nearly every practical question asked here.
Pushing back on Dr.CardioMD here. The mechanism is more central than most summaries suggest. Receptor agonism in the arcuate nucleus activates POMC neurons and inhibits AgRP/NPY signalling, and the downstream MC4R pathway is the same one disrupted in monogenic obesity — convergent genetic evidence that the target is the right one. Peripherally there is glucose-dependent insulin secretion, glucagon suppression and delayed gastric emptying, but the gastric component largely adapts over months while the central effect persists, which is why the durable effect is appetite rather than fullness.
PeptideDetective — Independent Peptide Analytics
Community-driven peptide testing and vendor rating platform. Transparent results. Unbiased analysis. Trusted by thousands.
View ResultsPurityPaulOR said:The mechanism is more central than most summaries suggest.
Receptor pharmacology relevant to the pharmacology: semaglutide is a GLP-1R agonist with a C-18 fatty acid chain that enables albumin binding (>99%), creating a depot effect with a ~168-hour half-life enabling weekly dosing[1].
Tirzepatide is a dual GIP/GLP-1R agonist with higher GIP affinity (5:1 GIP:GLP-1 potency ratio). The GIP component may enhance beta-cell function and adipocyte lipid metabolism beyond what GLP-1 alone achieves.
For the pharmacology, the pharmacology explains the clinical differences between these agents.
[1] Lau J, et al. J Med Chem. 2015;58(18):7370-7380.
DebRD_ATL said:PK/PD modeling for the pharmacology: understanding the pharmacokinetics helps optimize dosing.
Mine went the same way, slower. I had assumed I was the exception until I read this.