What is retatrutide? An investigational triple agonist, and what 44 lab records show

What retatrutide is

Retatrutide is the one people call "the next one," and for once that framing is roughly accurate.

It's also called LY3437943, which is the development code you'll see in trial listings.

The GLP-1 story has been a story about counting receptors. Semaglutide hits one. Tirzepatide hits two.

Retatrutide hits three.

It's a triple receptor agonist, activating GIP, GLP-1, and glucagon receptors. Our profile describes it as combining appetite and metabolic signalling pathways.

The glucagon receptor is the new addition, and it's an interesting one because glucagon does roughly the opposite of insulin. Recruiting it alongside the other two is a deliberate bet about energy expenditure rather than just appetite.

Whether that bet pays off is genuinely unsettled, which brings us to the part that matters most.

Nobody has approved it

Retatrutide is still in trials. No regulator has cleared it for any use.¹

That's not a paperwork delay. The studies that would show whether the benefits hold, and at what cost in harms, haven't finished.

We rate it moderate evidence with a developing record. That's a deliberately different box from the established record we give semaglutide and tirzepatide, and it's the only compound in our research directory sitting in the middle tier.

Our retatrutide profile summarises it as an investigational triple-receptor agonist with promising phase 2 weight-loss results and no FDA approval. Both halves of that sentence are load-bearing.

What the evidence actually is

Here's the whole of it, stated plainly.

A randomized phase 2 trial in 338 adults showed weight loss that scaled with the dose, over 48 weeks.²

That's a real result, and it's why anyone is paying attention. It's also far stronger than the animal-study hand-waving behind most unapproved peptides.

But it's mid-stage, and mid-stage means specific things are still unknown.

Phase 3 exists to answer the right-hand column.

Until it reports, "promising" is the honest word and "proven" isn't.

This is precisely the distinction we built the evidence-maturity framework around.

The strange part: it's the most-tested compound we track

Now the finding that surprised us.

Our testing ledger holds 117 published lab records across 11 compounds.³ Forty-four of them are retatrutide.

That's more than tirzepatide (33) and vastly more than semaglutide (2). The most heavily lab-tested compound in our entire ledger is one that no regulator has approved for anything.

Ledger records as published to date. Vendor counts from our price market, checked 25 July 2026.

Why? Because demand arrived before approval did. People want it now, a supply grew to meet that, and testing followed the money rather than the trial calendar.

Worth stating plainly: how much a thing gets tested tells you how much it's being sold, not how well it's been studied. Those move independently, and they're easy to confuse.

What those 44 records show

Of the 40 retatrutide records carrying dose data:

So purity holds up well, and the labelled dose doesn't.

That +43.5% is the largest single dose miss anywhere in our ledger. A vial sold as 10mg measured 14.35mg, at 99.859% purity. Clean material, wrong amount, by nearly half.

The pattern matches what we found for tirzepatide: identity and purity are mostly fine, and the number on the label is not a reliable statement of contents. Retatrutide is simply the compound where the spread is widest.

One caution on reading these records: several identical result sets in our ledger appear under multiple different vendor names, so the count of sellers with testing overstates how much independent testing exists. We go into that in how to evaluate a peptide vendor.

What it costs

Retatrutide runs $45.00 to $306.00 across the three vendors listing it, as of our 25 July 2026 check.

That's a 6.8x spread, the widest of any GLP-1-class compound in our market. Some of that is package size, and a range that wide on three listings still tells you there's no settled price for this.

Which is what you'd expect for something with no approved product to anchor against.

Where retatrutide sits

The most interesting unapproved peptide in the market, and still an unapproved one.

Genuinely promising. A randomized phase 2 result in 338 adults is far more than most compounds here will ever have.

Genuinely unfinished. Phase 3 hasn't answered the durability and safety questions, and nobody has cleared it for use.

Heavily sold and heavily tested, with the widest dose miss in our ledger and a price range spanning nearly seven-fold.

The mistake to avoid is letting all that activity stand in for maturity of evidence. Retatrutide is the clearest example we have of the two coming apart.

Compare the approved end of the class: tirzepatide and semaglutide. Or start at what peptides actually are.