Participants share scattered potency numbers from papers and AI lookups but note that albumin binding, biased signaling and dosing make direct KI comparisons unreliable. Retatrutide is described as lower potency at GLP-1 yet still the strongest overall weight-loss agent; tirzepatide is a biased GLP-1 agonist. Stacking is discussed as possibly adding little extra benefit beyond high-dose monotherapy while raising unknown risks, with one user citing personal tolerance differences across agents.
What this discussion establishesWhether KI values or AI summaries can usefully predict real-world receptor activation when agents are combined, and whether stacking carries meaningfully higher risk than simply raising the dose of one compound.
Still openExact numerical ratios of receptor activation when retatrutide is stacked with tirzepatide, and the safety margin of any GLP-1 combination at typical versus maximum doses.
Nothing here is advice.
Trying to phrase this without sounding off. Does anyone have the breakdown of how much each receptor type is activated by sema versus tirz versus reta? Sema looks heavier on GLP-1 while reta has lower GLP-1 plus GIP activity, so are the actual numbers known? If someone stacks reta with tirz, can we figure out the combined GLP-1 activation?
I was hoping for some replies on this but maybe the numbers just aren't out there.
A paper in NEJM says retatrutide was made to be less active at the GLP-1 receptor, about 0.4 times natural GLP-1, while staying very strong at the GIP receptor because of the triple-agonist design. I've seen somewhere that GIP potency is much higher but don't have the exact figure.
One of the better write-ups on the KI numbers covers GIP first, then GLP, then glucagon. Looking at maz though shows the limits of relying on those KI figures.
Thanks a lot for posting that. Really useful info.
The AI numbers are off. I've tried writing about this four times already. Spent ages digging through early papers and using scholar mode on chat gpt to hunt for natural GLP-1 agonists or modulators in herbs, back when I didn't know about research peptides. Binding numbers get messy because most of the drug sticks to albumin in blood, changing how it hits the receptor depending on whether the assay used the bound or free form. Tirzepatide also acts as a biased agonist at GLP-1, favoring cAMP over beta-arrestin so the receptor stays active longer.
You raise some key points. The AI already noted that affinity isn't the same as efficacy. An essay explains that even though most of a drug like sema is bound to albumin for stability, you just raise the dose until the free fraction activates the receptor enough. Maz shows why KI numbers alone can mislead; its numbers look weak yet it still works at higher doses plus dual agonism. A 6 mg maz dose ends up roughly equal to 8.6 mg of something with a seven-day half-life. The same essay argues against stacking GLP agonists and favors reta alone or with cagri.
You're right, some parts of the earlier post came through after I had already written mine. I agree reta is the strongest option for weight loss and the newest design, so receptor knowledge and modeling have advanced. Tirz may have slightly fewer sides but the difference isn't huge. Sema is weakest and has the most sides. If reta isn't enough the next logical step is usually cagri or eloralintide later, though GI effects often keep the add-on dose low. Side effects don't always follow the expected pattern; I got bad nausea from very low sema but almost none from moderate tirz.
An essay warns that stacking GLP-1 drugs may carry more risk than people realize because each one is already meant to fully turn on the receptor at normal doses, so adding another for extra appetite control could be risky. That feels concerning since some users are already trying it. Probably depends on the doses too, and more data would help.
I'm not sure what that line is getting at. Why would two separate GLP meds be riskier than just going higher on one?
I know it was a quote. I'm just saying the logic behind it doesn't click for me.
I agree dose level has to matter. The worry makes sense if both are already at max, but what happens when each is kept low?
Just to correct the quote a bit: these drugs don't merely fully activate the receptors; they push far above normal physiology, many times stronger than natural GLP-1 and lasting a full week instead of minutes. Top doses of any of them already sit near the ceiling of what the receptors can do, which is why further increases often stop adding weight loss. Risks of combinations are still unknown and there's little solid proof stacking is safe. The cagrisema study did show more weight loss than either drug alone but also more GI issues and not as big an improvement as hoped, with no surprise severe problems. Higher-dose sema trials at 7.2 mg and 16 mg also gave extra loss but again less than expected.
Someone logged in this morning on an extreme stack, which shows stacking isn't automatically dangerous, though that level would be too much for me.
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