Retatrutide (LY3437943) is an investigational 39-residue lipidated peptide from Eli Lilly that activates the GIP, GLP-1 and glucagon receptors. It was in phase 3 trials in October 2026.

How does retatrutide work?

It acts on three hormone receptors: GIP and GLP-1, the two incretin receptors, plus the glucagon receptor. In vitro its glucagon and GLP-1 activity was balanced, with more GIP activity. A C20 fatty diacid binds albumin and gives it a half-life of about six days.

Is retatrutide FDA-approved?

No. It is investigational and had not been approved by any regulator by October 2026. Press coverage of Lilly's July 2026 announcement reported a planned FDA submission in early 2027.

Is retatrutide the same as GLP-3?

"GLP-3" is a catalogue label for retatrutide, not a scientific name. There is no GLP-3 hormone or receptor; the label counts its three receptors.

What is the difference between retatrutide and tirzepatide?

Both are Eli Lilly peptides on the GIP backbone. Tirzepatide activates two receptors (GIP and GLP-1) and is FDA-approved; retatrutide adds the glucagon receptor and is investigational. A head-to-head phase 3 trial, TRIUMPH-5, was running in October 2026.

Who makes retatrutide?

Eli Lilly and Company, which also developed tirzepatide. Research catalogues, including ours (as GLP-3 Reta), sell retatrutide as a laboratory reference material that is not Lilly's product.

What Is Retatrutide? Triple Agonist, Structure & Trials

Retatrutide (LY3437943) is an investigational peptide from Eli Lilly that activates three hormone receptors at once: the GIP, GLP-1 and glucagon receptors. It is a 39-residue lipidated peptide given once weekly in trials, it was in phase 3 in October 2026, and it has not been approved by any regulator. Research catalogues sell it under the informal labels “GLP-3 R” and “GLP-3 RT”.

Retatrutide in one table

Developer	Eli Lilly and Company (code LY3437943)
Receptors	GIP receptor, GLP-1 receptor and glucagon receptor (triple agonist)
Built on	The GIP peptide backbone
Length	39 residues, C-terminal amide
Unnatural residues	Aib at positions 2 and 20; α-methyl-leucine at 13
Lipidation	C20 fatty diacid on Lys17 via a γGlu–AEEA linker
Formula / weight	C₂₂₁H₃₄₂N₄₆O₆₈, 4731.34 g/mol; CAS 2381089-83-2
Reported half-life	About 6 days (phase 1b, type 2 diabetes)
Status, October 2026	Investigational, phase 3; not approved anywhere
Other names	“Triple G” (PubChem record title); GLP-3, GLP-3 R, GLP-3 RT, Reta (catalogue labels)

Sources: the FDA substance registry (GSRS), KEGG DRUG D12430, PubChem CID 171390338 and the papers below.

How retatrutide works

Each of its three receptors belongs to a different hormone. GIP and GLP-1 are incretins, gut hormones released after a meal that act on the pancreas and elsewhere; glucagon is the pancreatic hormone that acts mainly on the liver. Earlier drugs targeted one of these receptors (semaglutide, GLP-1) or two (tirzepatide, GIP and GLP-1). Retatrutide combines all three in one molecule.

Lilly’s discovery paper reported that, in vitro, retatrutide’s activity at the glucagon and GLP-1 receptors was balanced, with more activity at the GIP receptor, and studied it in obese mice and a first human single-dose study. A 2024 structural study resolved how the single peptide binds each of the three receptors. LY3437943, a novel triple glucagon, GIP, and GLP-1 receptor agonist for glycemic control and weight loss: From discovery to clinical proof of concept. Coskun T, et al. Cell Metabolism, 2022; Li W, et al. Cell Discovery, 2024.

The C20 fatty diacid binds albumin in the blood, which slows clearance: the phase 1b study measured a half-life of about six days, which is what supports once-weekly dosing in the trials. Urva S, et al. Lancet, 2022.

Is retatrutide GLP-3?

No. There is no GLP-3 hormone and no GLP-3 receptor. “GLP-3” is a marketplace label that counts retatrutide’s three receptors, the way “GLP-2” is used for two-receptor tirzepatide, which has nothing to do with the real hormone GLP-2. Lilly itself calls the label scientifically inaccurate. The full explanation is in GLP-1 vs GLP-2 vs GLP-3: what the names mean.

The clinical trials

All retatrutide trials are Lilly-sponsored. Each link goes to the PubMed record or the registry entry.

Phase 1b (2022). A 12-week multiple-ascending-dose study in 72 people with type 2 diabetes, which measured the half-life. Urva S, et al. Lancet, 2022.
Phase 2 (2023). A 48-week trial in 338 adults with obesity or overweight, and a 36-week trial in 281 adults with type 2 diabetes against placebo and dulaglutide. Triple-Hormone-Receptor Agonist Retatrutide for Obesity – A Phase 2 Trial. Jastreboff AM, et al. NEJM, 2023; Rosenstock J, et al. Lancet, 2023.
TRIUMPH-1 and TRIUMPH-2 (2026). 80-week phase 3 trials in 2,339 adults with obesity and 1,152 adults with obesity and type 2 diabetes, both reporting on their primary body-weight end points. Retatrutide, a Triple Hormone Receptor Agonist, for Treatment of Obesity. Jastreboff AM, et al. NEJM, 2026; Bellido V, et al. Lancet, 2026.
TRANSCEND-T2D-1 (2026). A 40-week phase 3 trial in 537 adults with type 2 diabetes, with HbA1c as the primary end point. Bajaj HS, et al. Lancet, 2026.
Still running in October 2026. TRIUMPH-3 to -9, the head-to-head TRIUMPH-5 against tirzepatide (NCT06662383), a phase 3 trial against semaglutide in type 2 diabetes (NCT06260722) and the 10,000-person TRIUMPH-Outcomes cardiovascular and kidney trial (NCT06383390).

Gastrointestinal events were the most common adverse events across the published trials.

Regulatory status

Retatrutide is investigational. No regulator had approved it by October 2026, and Lilly’s own FAQ describes it that way. Press coverage of Lilly’s July 2026 announcement reported a planned submission to FDA in early 2027. Lilly also lists a pre-approval expanded-access programme on ClinicalTrials.gov (NCT07629401).

How it compares

Retatrutide vs tirzepatide: three receptors against two, both from Lilly.
Retatrutide vs semaglutide: three receptors against one.
Survodutide vs mazdutide vs tirzepatide vs retatrutide: the multi-receptor peptides side by side.

Retatrutide for laboratory research

Clean Peptide stocks retatrutide as GLP-3 Reta, a lyophilised reference material in several sizes, each analysed by ILS Laboratories with identity confirmed against a retatrutide reference standard. Prices per vial and per milligram are in retatrutide price. It is not Lilly’s product and is not for human or veterinary use.