Dr.GastroMayo said:

The pharmacokinetics explain nearly every practical question asked here.

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.

Dr.GastroMayo said:

The pharmacokinetics explain nearly every practical question asked here.

This is where I part company with the consensus forming above. 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.

LarryQC_SD said:

The mechanism is more central than most summaries suggest.

Pharmacist here. I want to add the drug interaction perspective on the pharmacology.

Key points from a pharmacokinetic standpoint:

• GLP-1 agonists delay gastric emptying, which can affect Tmax of co-administered oral medications
• Monitor patients on warfarin (INR), levothyroxine (TSH), and oral contraceptives during dose titration
• The albumin-binding mechanism of semaglutide (C-18 fatty acid linker) gives it the ~168-hour half-life that enables weekly dosing
• Steady state is reached at approximately 4-5 weeks after dose initiation or adjustment

Re: the pharmacology specifically — the pharmacology here is well-characterized and the clinical implications are straightforward.

Dr.SurgeonPGH said:

Receptor pharmacology relevant to the pharmacology: semaglutide is a GLP-1R agonist with a C-18 fatty acid chain that enables albumin binding (>99%),…

Second this. Posting only so the count is not one.