Research guide / Retatrutide

What is Retatrutide? A Complete Research Guide.

Updated August 2026 · 12 minute read

Retatrutide is an investigational peptide being studied as a single molecule that activates three hormone receptors. This guide separates what peer-reviewed studies show from what is still being tested, sponsor-reported, or assessed by regulators.

Research information only. This article summarises published and registered research. It is not medical advice, a dosing guide, or evidence that retatrutide is approved for treatment. Trial averages do not predict an individual outcome.

01 / Overview

What is retatrutide?

Retatrutide, also known by the development code LY3437943, is a long-acting investigational peptide developed by Eli Lilly. It activates the receptors for glucose-dependent insulinotropic polypeptide (GIP), glucagon-like peptide-1 (GLP-1), and glucagon in one molecule.[1]

Because it acts at three receptors, it is often called a triple agonist. That description refers to laboratory pharmacology; it does not mean the medicine has passed regulatory review or that its benefits and risks are fully established.

Researchers are studying retatrutide in obesity, type 2 diabetes, cardiovascular and kidney outcomes, and related metabolic conditions. Its clinical programme remains a mixture of completed studies, active trials, peer-reviewed publications, and sponsor-reported results.

View the Retatrutide research listing

02 / Mechanism

How does retatrutide work?

Retatrutide is designed to bind to and activate three receptors involved in nutrient sensing and energy regulation. The effects of activating them together are still under investigation.[1]

Pathway	Normal signalling role	Research relevance
GLP-1 receptor	Participates in glucose-dependent insulin signalling, satiety signalling, and gastric function.	A well-studied incretin target; retatrutide adds GIP and glucagon receptor activity.
GIP receptor	Participates in nutrient-responsive, glucose-dependent insulin signalling.	Researchers are examining how combined GIP and GLP-1 activity influences metabolic responses.
Glucagon receptor	Participates in hepatic glucose regulation and energy metabolism.	Its addition distinguishes retatrutide from single and dual incretin agonists; its exact human contribution remains under study.

The combined hypothesis is that GLP-1 and GIP signalling may influence appetite and glucose-dependent insulin responses, while glucagon-receptor activity may affect energy expenditure and liver metabolism. The contribution of each pathway to human outcomes cannot be separated from these trials and should not be treated as settled.

03 / Published evidence

Peer-reviewed findings

In the 48-week Phase 2 obesity trial, 338 adults were randomised to retatrutide or placebo. Mean body-weight change at week 48 ranged from −8.7% at 1 mg to −24.2% at 12 mg, compared with −2.1% for placebo. These are group averages from a controlled trial, not expected individual results.[1]

A 98-participant substudy of the same Phase 2 trial examined liver fat in participants with at least 10% liver fat. At week 24, mean relative changes ranged from −42.9% at 1 mg to −82.4% at 12 mg, versus +0.3% with placebo. This was a selected substudy and does not establish an approved use.[2]

In the 40-week TRANSCEND-T2D-1 Phase 3 trial, 537 adults with type 2 diabetes inadequately controlled by diet and exercise were randomised. The Lancet paper reported mean HbA1c changes of −1.69% to −1.94% across retatrutide groups versus −0.81% with placebo, and mean body-weight changes of −11.5% to −15.3% versus −2.6%. The trial was funded by Eli Lilly.[3]

04 / Trial registry

Registered clinical programme

A registry record shows what a study was designed to test and its reported recruitment status. It does not by itself establish efficacy, safety, or approval.

Programme	Trial ID	Population	Registry status
TRIUMPH-1	NCT05929066	Obesity or overweight, without type 2 diabetes	Completed · 2,335 participants
TRIUMPH-2	NCT05929079	Obesity or overweight with type 2 diabetes	Completed · 1,152 participants
TRIUMPH-3	NCT05882045	Severe obesity with established cardiovascular disease	Completed · 1,946 participants
TRIUMPH-4	NCT05931367	Obesity or overweight with knee osteoarthritis	Completed · 445 participants
Head-to-head Phase 3	NCT06662383	Retatrutide compared with tirzepatide in obesity	Active, not recruiting · estimated 800
TRIUMPH-Outcomes	NCT06383390	ASCVD and/or chronic kidney disease	Active, not recruiting · estimated 10,000
TRANSCEND-T2D-3	NCT06297603	Type 2 diabetes with moderate or severe renal impairment	Active, not recruiting · estimated 320

Statuses and enrolment figures reflect the original ClinicalTrials.gov records reviewed for this August 2026 update. Registry records can change.[4], [5], [6], [7], [8], [9], [10]

Afiya Labs lists a Retatrutide reference material for laboratory research. The catalogue entry is not a medicine listing and is not presented as suitable for human use.

See the Retatrutide catalogue entry

05 / Sponsor report

Sponsor-reported Phase 3 topline results

In May 2026, Lilly reported that TRIUMPH-1 participants assigned to 12 mg had a mean body-weight change of −28.3% at 80 weeks, compared with −2.2% for placebo, using the efficacy estimand. The company also reported that 45.3% of that group reached at least 30% weight reduction.[11]

On 23 July 2026, Lilly reported topline results from two more Phase 3 trials, using the efficacy estimand. In TRIUMPH-2 (NCT05929079; 1,152 adults with type 2 diabetes and obesity or overweight), mean body-weight change at 80 weeks was −12.7%, −19.1% and −20.8% with 4 mg, 9 mg and 12 mg, versus −4.0% with placebo; mean A1C change from a 7.7% baseline was −1.4%, −1.6% and −1.5%, versus −0.2%. In TRIUMPH-3 (NCT05882045; 1,949 adults with severe obesity and established cardiovascular disease), mean body-weight change was −21.6% with 9 mg and −22.6% with 12 mg, versus −3.2% with placebo. Lilly said it plans to submit a US marketing application in Q1 2027.[15]

These figures come from Lilly’s original announcements. At the time of this update, they should be read as sponsor-reported topline findings: they are not peer-reviewed, have not been evaluated by regulators, and do not establish approval. Note that enrollment figures for the same trial differ between ClinicalTrials.gov and Lilly’s announcements; each figure is cited here as its source reports it.

Shop Retatrutide pen

06 / Safety evidence

What safety findings have trials reported?

In the Phase 2 obesity trial, the most common adverse events were gastrointestinal. They were dose-related, mostly mild to moderate, and partly reduced by using a lower starting dose. Dose-dependent heart-rate increases peaked at week 24 and then declined during the trial.[1]

TRANSCEND-T2D-1 reported that the most frequent adverse events were generally mild-to-moderate gastrointestinal events that subsided over time. Discontinuation due to adverse events occurred in 2–5% of retatrutide groups and 0% with placebo; no severe hypoglycaemia was reported.[3]

These studies do not answer every long-term safety question. Adverse-event findings depend on the studied population, follow-up period, dose-escalation design, and controlled trial conditions. There is no approved prescribing information for retatrutide.

07 / Regulators

Approval status in the US, Europe, and UAE

United States

FDA’s current statement on unapproved GLP-1 drugs says retatrutide cannot be used in compounding under federal law, is not a component of an FDA-approved drug, and has not been found safe and effective for any condition. An earlier FDA warning letter (9 September 2025) is supporting historical evidence. This concerns US federal regulation only; it is not a global legal opinion.[16], [12]

European Union

The EMA issued a paediatric investigation plan decision for retatrutide in September 2024. A paediatric plan is a development requirement and is not a marketing authorisation, positive opinion, or finding that benefits outweigh risks.[13]

United Arab Emirates

The Emirates Drug Establishment maintains the UAE’s public registered medical product directory. We did not identify a retatrutide-specific public decision in the official material reviewed for this update. Directory presence or absence is not used here to infer approval, non-approval, legality, availability, or permission for use; those questions require confirmation from the EDE.[14]

08 / Quick answers

Frequently asked questions

Is retatrutide an approved medicine?

No approval should be inferred from clinical research. The FDA source cited here describes retatrutide products as unapproved, and the EMA record cited here is a paediatric development decision rather than a marketing authorisation.

Why is it called a triple agonist?

It activates three receptor families in one molecule: GIP, GLP-1, and glucagon. The term describes its pharmacology, not its approval status.

Has retatrutide reached Phase 3?

Yes. Multiple Phase 3 studies are registered, and TRANSCEND-T2D-1 has been published in The Lancet. Some TRIUMPH results remain available only as sponsor-reported topline data.

What did the Phase 2 obesity study find?

The 48-week trial reported dose-dependent mean body-weight changes, reaching −24.2% in the 12 mg group versus −2.1% with placebo. This was a controlled trial average, not a forecast for individuals.

What side effects were seen in trials?

Gastrointestinal events were most common in the cited trials. The Phase 2 obesity paper also reported a temporary, dose-dependent increase in heart rate. Long-term outcomes are still being studied.

What does the UAE directory show?

It is a public register of medical products. This guide does not turn a directory search result—or the absence of one—into a claim about approval, legality, or permitted use. The EDE is the appropriate authority for a current determination.

09 / Sources