Oral vs injectable GLP-1: bioavailability and efficacy comparison — May 2025

ingrid_STO said:

Reading about receptor desensitisation and trying to work out which of the effects adapt over time and which do not, because people clearly experience…

Semaglutide structural biology relevant to the pharmacology: semaglutide is a 31-amino acid peptide with 94% homology to native GLP-1(7-36). Three key modifications enable its pharmacokinetic profile:

1. Aib8 substitution: DPP-4 resistance (prevents enzymatic degradation)
2. Arg34 substitution: improved chemical stability
3. C18 fatty diacid at Lys26: albumin binding → long half-life

These three modifications transform a peptide with a 2-minute half-life (native GLP-1) into one with a 168-hour half-life (semaglutide). A masterclass in peptide engineering.

amsterdam_pete said:

Semaglutide structural biology relevant to the pharmacology: semaglutide is a 31-amino acid peptide with 94% homology to native GLP-1(7-36).

That is correct as far as it goes, and here is where it stops going. 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.

ingrid_STO said:

Reading about receptor desensitisation and trying to work out which of the effects adapt over time and which do not, because people clearly experience…

This is my experience too, for whatever a second data point is worth. Nothing to add that would improve it.

Clinical perspective, offered as context rather than as advice.

Amycretin (AMY/GLP-1 dual agonist) emerging data relevant to the pharmacology: Phase 1 showed -13.1% body weight at only 12 weeks, the fastest trajectory ever seen for an anti-obesity agent[1].

Amylin receptor agonism enhances satiety signaling through the area postrema and reduces glucagon secretion. Combined with GLP-1R agonism, this dual mechanism may produce even greater efficacy than current agents.

Early-stage data — interpret with caution. But the trajectory is extraordinary.