How many weeks to steady state for orforglipron on a weekly schedule?

This matters because it predicts what a related molecule should do.

The units are where I keep going wrong, so please be explicit about them.

I have sanity-checked the order of magnitude and it seems right, which is not the same as being right.

Where is my error, and what is the correct working?

The honest answer is that appetite suppression is centrally mediated and gastric emptying is peripheral, and the two contribute different amounts in different people.

Receptor density and downstream coupling differ between tissues, so the dose-response curves for glycaemia, weight and nausea are not the same curve. That is the pharmacological basis for titration.

Native GLP-1 has a circulating half-life of one to two minutes because dipeptidyl peptidase-4 cleaves the two N-terminal residues. Substituting the position-8 alanine, as the long-acting analogues do, blocks that cleavage and is the single most consequential modification in the class.

Glucose-dependence is the property to remember; it explains the safety profile on its own.

The glucose-dependence is the key property. Below about four millimoles per litre the insulinotropic effect largely disappears, which is why monotherapy hypoglycaemia is uncommon.

Glucagon suppression is also glucose-dependent and is lost during hypoglycaemia, which preserves the counter-regulatory response — a genuinely elegant piece of physiology and the reason the class is safe in this respect.

Biased agonism — differential recruitment of beta-arrestin versus G-protein signalling — is an active research area and is one hypothesis for why agents with similar receptor affinity have different tolerability.

Structural work on the receptor by cryo-electron microscopy has resolved the agonist-bound active state and is the basis for current structure-guided design in this class.

Nausea and appetite share an anatomy, which is why they are hard to separate by dose.

This is answerable mechanistically, and the mechanism actually predicts the side-effect profile, which is unusual and worth exploiting when reasoning about it.

Albumin binding does the rest of the work. A fatty-acid chain attached through a linker binds circulating albumin reversibly, which both shields the peptide from renal clearance and creates a depot; that is how a two-minute hormone becomes a once-weekly drug.

Gastric emptying delay attenuates with continued exposure for long-acting agents through receptor desensitisation, which is why the early nausea usually settles while the appetite effect persists.

Research-use material is not approved for human use, and mechanism is not a safety argument.

The half-life problem and the albumin-binding solution are the whole story of the class chemically.

edited 13 Jun 2025 by k_szabo — fixed an arithmetic slip in the third paragraph

The receptor is also expressed in the heart, kidney and vasculature, which is the plausible route for effects that are not obviously metabolic.

Central effects reach the arcuate nucleus and the area postrema, regions with an incomplete blood-brain barrier. That anatomy is why a large peptide can act centrally at all, and it also explains the nausea, since the area postrema is the chemoreceptor trigger zone.

Area postrema involvement in nausea from this class is supported by lesion studies in animals and by the anatomy of the circumventricular organs.

The caveat is that mechanism predicts direction and rarely predicts magnitude in an individual, and people reason from mechanism to dose far too confidently.

Tissue distribution first, then signalling. Nearly every question in this tag resolves at the first step.

Start with the tissue distribution. Pancreatic islet, gastric, and several hypothalamic and brainstem populations — that list explains insulin secretion, gastric emptying and appetite in one go.

Glucose-dependence arises because the insulinotropic signal amplifies glucose-stimulated secretion rather than initiating secretion. With no glucose signal to amplify, there is little to amplify.

Nothing here is medical advice; this is pharmacology.

Mechanism is a good guide to what to expect and a poor guide to how much.