Retatrutide is investigational: what that status means
Retatrutide (LY3437943) is Eli Lilly's single-peptide agonist of the GIP, GLP-1 and glucagon receptors, with no FDA-approved product as of September 2026. What 'investigational' means, and why a research vial is not the trial drug.
Retatrutide is not an FDA-approved drug as of September 21, 2026. It is an investigational new drug: Eli Lilly's compound LY3437943, a single synthetic peptide that acts as an agonist at the GIP, GLP-1 and glucagon receptors, being studied in a Phase 3 program under an investigational new drug application. "Investigational" is a legal status with a precise meaning in 21 CFR part 312, and a research-grade vial labelled retatrutide is not the drug in those trials, cannot be represented as it, and is not sold here for any purpose other than laboratory research.
What retatrutide is
Retatrutide is a synthetic peptide developed by Eli Lilly and Company under the code LY3437943. The peer-reviewed description is consistent across the program's publications: the 2022 Lancet paper calls it "a single peptide with agonist activity for glucagon, glucose-dependent insulinotropic polypeptide (GIP), and glucagon-like peptide 1 (GLP-1) receptors," the 2022 Cell Metabolism paper calls it "a novel triple agonist peptide" at the same three receptors, and the 2023 New England Journal of Medicine Phase 2 report opens with "Retatrutide (LY3437943) is an agonist of the glucose-dependent insulinotropic polypeptide, glucagon-like peptide 1, and glucagon receptors." That is why it is called a triple agonist, and why it sits on our GLP-1 analogue shelf next to semaglutide and tirzepatide.
PubChem carries the molecule as CID 171934787, with the formula C221H342N46O68 and a molecular weight of 4731. It is a large peptide by the standards of this catalog, and its identity on a certificate rests on mass spectrometry rather than on a sequence anyone can read off a label. We list retatrutide as a lyophilized research vial and, as a catalog item only, a retatrutide and cagrilintide blend. Neither is the trial material.
What "investigational" means in law
Under 21 CFR 312.3, an investigational new drug is "a new drug or biological drug that is used in a clinical investigation," and a clinical investigation is "any experiment in which a drug is administered or dispensed to, or used involving, one or more human subjects." The mechanism that makes those experiments lawful is the IND, the investigational new drug application, which the same regulation defines and which FDA's own page describes as "the means through which the sponsor technically obtains this exemption from the FDA." The exemption is from section 505(a) of the Federal Food, Drug, and Cosmetic Act, which prohibits introducing any new drug into interstate commerce without an approved application. FDA's IND page puts the rule plainly: "Current Federal law requires that a drug be the subject of an approved marketing application before it is transported or distributed across state lines."
An IND is therefore not a lesser approval. It is a sponsor-specific, study-specific permission to ship a specific material to specific investigators for a specific study, after a thirty-day FDA review window. Everything about it is bound to the sponsor and the study. The drug substance is made to the sponsor's specification under the quality system described in the IND, released against the sponsor's tests, labelled for the investigation, and dispensed only inside it. Nothing in that chain touches a research chemical supplier.
Where the retatrutide program stands
ClinicalTrials.gov listed 33 records for retatrutide on September 21, 2026. Thirty-two have Eli Lilly and Company as lead sponsor; one is a Phase 2 study by Hudson Biotech. The Lilly records run from completed Phase 1 studies through a set of Phase 3 studies, several of them completed (for example NCT05929066 and NCT05882045) and several active but no longer recruiting (NCT06383390, the TRIUMPH-Outcomes study, NCT06859268 and NCT07357415 among them). One record, NCT07629401, is a pre-approval expanded-access listing with the status "available," which is a mechanism for a sponsor to supply an investigational drug outside its trials under FDA's rules, and which exists precisely because the drug is not approved.
No retatrutide product appears in Drugs@FDA. Whether or when Lilly files or has filed a marketing application is not something this piece can state from a primary source, so it does not. What can be stated is the status on the date: investigational, Phase 3, no approved product. FDA's warning letters of 2024 and 2026 name "Retatrutide" sold by research suppliers as an unapproved new drug, which is the same status seen from the enforcement side.
Why a research vial is not the trial drug
The question behind "is retatrutide available" is usually whether a vial sold as retatrutide is the same thing Lilly is studying. It is not, and the reasons are structural rather than a matter of quality.
- The trial drug exists inside an IND. It is made by or for the sponsor, to the sponsor's specification, and released by the sponsor. A research vial is made by a manufacturer we name, to a research-grade specification, and released against a certificate of analysis. The two are different articles with different paperwork, even where the peptide sequence is the same.
- The trial drug is a finished, formulated product. A research vial is a lyophilized solid, the raw peptide and its counter-ion. What a formulated product contains, and why it is a different article, is set out in buffer, pH and preservative.
- The trial drug carries the sponsor's identity, and no one else may claim it. FDA's letters to peptide sellers in 2026 were written in part because sellers borrowed that identity. The letter to Royal Peptides, dated August 24, 2026, reproduces a sentence from the seller's retatrutide page that quoted a body-weight percentage from a trial the seller had nothing to do with, and concludes from the website that the products were intended as drugs for human use; the letters and their reasoning are set out in what FDA reads before calling a research product a drug.
A research supplier that describes its vial with the sponsor's data is representing its product as the investigational drug, which it is not entitled to do and which is not true.
This site publishes no trial figures on any product page; what it does publish is described on the provenance page.
Why the availability question has an honest answer
Retatrutide exists as a drug only inside Lilly's program, in its studies and in the expanded-access record on ClinicalTrials.gov. It is not available as a medicine in any pharmacy, because there is no approved product, and it is not lawfully compoundable, because it meets none of the conditions section 503A sets for a bulk substance; 503A, 503B and research use only sets those conditions out. The end of the compounding window for its approved relatives, semaglutide and tirzepatide, is dated in what ended for compounded semaglutide and tirzepatide, and when.
A research vial is not a route to the trial drug or a substitute for a prescription product that does not exist. It is labelled research use only because that is what it is for.
Status table
| Question | Answer | Source |
|---|---|---|
| Sponsor and code | Eli Lilly and Company, LY3437943 | ClinicalTrials.gov; Lancet 2022 |
| What it is | Single peptide, agonist at GIP, GLP-1 and glucagon receptors | Lancet 2022; Cell Metabolism 2022; NEJM 2023 |
| Formula and mass | C221H342N46O68, MW 4731 | PubChem CID 171934787 |
| FDA-approved product? | No | Drugs@FDA |
| Development stage | Phase 3; several studies completed, several active | ClinicalTrials.gov, 33 records, September 21, 2026 |
| Expanded access? | NCT07629401 listed as available (pre-approval) | ClinicalTrials.gov |
| 503A compounding pathway? | None: no monograph, no approved parent, not on the bulks list | FD&C Act 503A; FDA 503A page |
| Named in FDA letters? | Yes, as an unapproved new drug (Prime Peptides, December 10, 2024; Gram Peptides, March 31, 2026; Royal Peptides, Peptide Partners, Peak Performance Peptides, August 24, 2026) | FDA warning letters |
| Status of this site's vial | Research use only; not the trial drug | This page |
Every status line in this table is dated September 21, 2026 and will change; the piece is scheduled for review on any filing or approval. The wider set of molecule status lines is collected in Approved, investigational, or neither: a status table.
Sources
- Retatrutide (sodium salt), PubChem CID 171934787, National Library of Medicine
- ClinicalTrials.gov records for retatrutide, National Library of Medicine, queried September 21, 2026
- Urva S et al., LY3437943, a novel triple GIP, GLP-1, and glucagon receptor agonist in people with type 2 diabetes, Lancet, 2022 (PubMed 36354040)
- Coskun T et al., LY3437943, a novel triple glucagon, GIP, and GLP-1 receptor agonist, Cell Metabolism, 2022 (PubMed 35985340)
- Jastreboff AM et al., Triple-Hormone-Receptor Agonist Retatrutide for Obesity, New England Journal of Medicine, 2023 (PubMed 37366315)
- 21 CFR 312.3, Definitions and interpretations, govinfo, 2024 edition
- Investigational New Drug (IND) Application, FDA, content current as of September 16, 2026
- 21 U.S.C. 355, New drugs, U.S. Code, current
- Bulk drug substances used in compounding under section 503A, FDA, content current as of May 14, 2026
- Warning letter to Royal Peptides LLC, FDA, August 24, 2026
- Warning letter to Prime Vitality, Inc. dba Prime Peptides, FDA, December 10, 2024
For laboratory research use only. Not a drug, not a supplement, and nothing here is a claim about what any of this material does in a person or an animal.