Retatrutide (GLP-3 RT / LY3437943): specifications and price per milligram

Identity and aliases

Retatrutide is a synthetic single-molecule agonist at the GIP, GLP-1 and glucagon receptors, carrying CAS 2381089-83-2 and a parent-peptide molecular weight around 4731.3 g/mol. It is a 39-amino-acid peptide with Aib substitutions at positions 2 and 20, an alpha-methyl-Leu at 13, and a lipidated Lys17.

You will find it listed as GLP-3, GLP-3 (RT), GLP-3 RT and LY3437943. Those are all the same compound. We use the aliases here because that is what the catalogs use, not because there is anything coy about the naming.

What the published literature contains

Discovery and receptor pharmacology have been characterized in vitro and in rodent models (Coskun et al., Cell Metabolism 2022). A phase 2 study in adults with obesity examined body-weight change and metabolic parameters over 48 weeks (Jastreboff et al., New England Journal of Medicine 2023). Sponsor-reported phase 3 topline results were announced in 2026; the molecule remains investigational and is not approved by the FDA.

That literature describes a clinical development program run by its sponsor under regulatory oversight. It is not a description of this material, which is supplied for laboratory research and is not an approved medicine.

Certificate requirements for a modified peptide

A lipidated 39-mer is a harder synthesis than a 15-residue unmodified peptide, and the certificate should reflect that.

• Mass spectrometry identity consistent with the lipidated parent, not just with a peptide backbone.
• HPLC purity as area percent with the chromatogram, so related substances are visible.
• Lot number matching the vial.

Price per milligram across the size ladder

The ladder runs 10mg, 20mg, 30mg and 60mg. List pricing falls from $7.00/mg at 10mg to $3.08/mg at 60mg. Member pricing on those rows is $4.50/mg and $2.08/mg. The full ladder is visible on the product page.

No one price wins every row. See the metabolic price comparison for matched sizes and dated competitor prices.

One molecule, three receptor targets

Retatrutide was designed as a single peptide with activity at the GIP, GLP-1 and glucagon receptors. Calling it a triple agonist describes that receptor-pharmacology design. It does not mean that the three signals have equal strength, equal duration or equal relevance in every assay. Those details depend on the experimental system and the comparison molecule.

The 2022 discovery paper reports cell-based receptor assays and animal experiments. Those layers answer different questions: a receptor assay can characterize potency under defined laboratory conditions, while an animal model adds distribution, metabolism and whole-organism measurements. Neither layer should be rewritten as a result about an untested research vial.

Aliases create a second problem. GLP-3 is a market nickname, not the name of a third endogenous incretin hormone. A complete specification should lead with retatrutide or LY3437943 and use GLP-3 only as a search alias, so the name does not substitute for the molecular identity.

Why the sequence modifications matter

Retatrutide is a modified 39-residue peptide rather than an unmodified native sequence. Its nonstandard residues and lipid side chain are part of the intended molecule. A reference mass that ignores those features would describe a different analyte, even if most of the amino-acid backbone were present.

Long, modified peptides can generate closely related synthesis products: shortened sequences, incomplete coupling products, oxidation products and material with an incorrect or incomplete side-chain modification. Chromatography helps separate the principal component from related material, while mass spectrometry asks whether the principal species is consistent with the intended structure.

That is why a purity number alone is incomplete. A dominant chromatographic peak can still belong to the wrong structure, and a correct mass signal does not quantify every related peak. The two methods answer complementary questions.

A development timeline is not a product certificate

The 2023 phase 2 publication describes a sponsor-run clinical study in adults with obesity over 48 weeks. That paper concerns material manufactured and administered under a clinical protocol. It is evidence about the investigational molecule in that program, not evidence about the identity, purity or quantity of a catalog vial.

As of 2026, Lilly reports phase 3 topline results and says regulatory submission is planned, while also stating that retatrutide is not approved. A development milestone can change quickly, so this page links to the sponsor's current status rather than turning an old milestone into a permanent sentence.

The distinction matters commercially. An investigational name, a published paper and a research-material listing may share a molecular label, but they do not share a manufacturing record, release decision or regulatory status.

Reading the phase 2 paper with its boundaries intact

A careful reading starts with the protocol: enrolled population, randomization, comparator, duration, prespecified endpoints, discontinuations and missing-data method. A percentage in the abstract is the end of that chain, not the beginning.

Dose groups in a clinical protocol are part of the study design and are not instructions for using research material. This site does not translate a clinical schedule into administration guidance, and it does not imply that a catalog product is interchangeable with the sponsor's investigational product.

Funding and authorship also belong in the record. Sponsor involvement is expected in a development program, but it should remain visible beside study design, replication and publication so a reader can judge the evidence rather than relying on a headline.

What a release record should show

• The full intended identity, including the modified residues and lipid side chain.
• Expected and observed mass with the mass convention stated.
• A chromatographic trace, method and integrated peak table for reported purity.
• Nominal vial mass and measured mass shown as separate fields.
• A lot or sample link that connects the result to the physical inventory.

A report can be technically detailed and still fail the last step. If its sample number cannot be connected to the inventory offered for sale, it is a historical test record, not a lot-matched certificate for that offer.

The public site may deliberately expose fewer fields than the private release record. That presentation choice must never enlarge the claim. A summary labeled historical remains historical, and an observed result remains tied to the tested sample.

How to read the historical 20mg sample summary

The public testing table includes a third-party retatrutide sample labeled 20mg, with measured mass and reported purity. It is shown because those two results help a reader understand the difference between nominal quantity and observed quantity.

It is not presented as a certificate for current Effect inventory. The source report is retained privately and its verification identifiers are not redistributed. That protects the source document without pretending the abbreviated table is a full report.

A future saleable lot still needs its own linked result. Product name and vial size are not enough to carry a test result from one batch to another.

Price comparisons need a matched denominator

Retatrutide listings span multiple vial sizes, so the vial price is not a useful ranking by itself. Divide the public price by the labeled mass, compare the same size or the same unit basis, and keep access fees and shipping in the delivered cost.

Measured mass should not silently replace labeled mass in a market comparison. The labeled mass is the promised commercial unit; measured mass is a result for one sample. Keeping both fields visible prevents a favorable historical result from inflating the advertised offer.

A lower price per milligram does not answer identity, composition or lot linkage. Price and analytical evidence belong in the same buying record, but neither is a proxy for the other.

Primary records and current status

• Coskun et al., 2022, discovery and receptor pharmacology: PubMed record.
• Jastreboff et al., 2023, phase 2 randomized trial: PubMed record.
• Lilly's current development summary, including 2026 status and the statement that the molecule is not approved: sponsor update.
• FDA information on unapproved GLP-1-related products: FDA statement.

Receptor potency depends on the assay

Potency values are produced inside an assay system. Receptor expression, cell background, signaling readout, incubation time and reference agonist can all affect the numerical estimate. Values from different papers should not be ranked without checking whether the systems are comparable.

A balanced or biased activity description likewise depends on the measured pathways and analytical model. The phrase can summarize an experiment, but it should not become an assay-free property attached to every sample bearing the molecule's name.

For that reason, this hub describes the three receptor targets but directs readers to the discovery paper for method-specific potency data. The primary table preserves more information than a rounded marketing number.

Sponsor milestones and independent sources

Sponsor updates are the most direct source for development timelines and planned submissions, but they are not a substitute for peer-reviewed study reports or regulatory decisions. Each source type should be used for the question it is positioned to answer.

A phase 3 topline announcement can precede a full publication and detailed regulatory review. The accurate status statement may therefore be that results were announced while full methods or analyses remain to be evaluated publicly. Planned submission is not approval.

The page should be reviewed when a full publication, filing or regulator decision appears. Until then, current-status language should remain dated and restrained.

A modified-peptide investigation checklist

1. Confirm the intended sequence, substitutions and side-chain structure in the specification.
2. Compare expected and observed species using the laboratory's stated mass convention.
3. Inspect the chromatographic trace and related-peak integration rather than the headline alone.
4. Keep measured quantity, purity and identity as distinct release fields.
5. Resolve sample-to-lot linkage before attaching the result to inventory or a public page.

If a result is ambiguous, the correct state is quarantine or clarification, not a stronger public summary. The checklist exists so a difficult synthesis does not receive looser documentation simply because it is difficult.

What the research page can and cannot establish

This page can define the intended molecule, summarize primary published records, state current development status with a date, explain analytical requirements and make the public price denominator visible. Those are discrete, checkable jobs.

It cannot establish that a future vial matches a sponsor's study material, that a historical sample describes current inventory or that a clinical result transfers to material outside the protocol. Those conclusions would require evidence the page does not possess.

Keeping those limits explicit protects the useful parts of the page. Readers can compare specifications and evidence without being asked to accept a broader product claim hidden inside the literature summary.

Review dates make the division durable. Development milestones can be refreshed from sponsor and regulatory sources, while analytical results remain attached to their original samples. One changing record does not silently rewrite the other. The source list and page date also show a later reviewer exactly where to begin the next update.