What Is Retatrutide? Triple Agonist GLP-1/GIP/Glucagon Profile

What Is Retatrutide?

Retatrutide (development code LY-3437943) is Eli Lilly’s investigational obesity and type 2 diabetes peptide: a single engineered peptide designed for once-weekly subcutaneous use that activates three hormone receptors at the same time — GLP-1, glucose-dependent insulinotropic polypeptide (GIP), and glucagon. Researchers usually shorten the name to “reta” or “reta peptide,” and some UAE suppliers market it as “GLP-3” (or “GLP3”) — a misnomer, since there is no GLP-3 receptor and retatrutide acts on the GLP-1, GIP, and glucagon receptors. In practical terms, retatrutide targets the receptor systems that help regulate hunger, blood sugar, and energy expenditure, which is why it sits at the centre of current interest in newer triple agonist drugs for metabolic disease research. Unlike CagriSema, which co-formulates two separate molecules in one injection, retatrutide works through one molecule that binds and activates all three targets at once:

• GLP-1 receptor — the same target as semaglutide (Ozempic/Wegovy) and the GLP-1 arm of tirzepatide.
• GIP receptor — the same target as tirzepatide’s second arm.
• Glucagon receptor — a third arm not present in any currently approved obesity agent.

Dosing is once-weekly subcutaneous, matching the administration pattern of semaglutide and tirzepatide. Phase 2 tested 1, 4, 8, and 12 mg weekly maintenance doses. If approved, retatrutide would become the first triple agonist on market and Eli Lilly’s next-generation successor to tirzepatide. For regulatory tracking, see Is retatrutide approved?

Mechanism of Action

The retatrutide hypothesis is that the three receptor arms are mechanistically complementary, not redundant. Each arm addresses a different component of body-weight regulation:

• GLP-1 receptor: Central appetite suppression and slowed gastric emptying to reduce appetite. This is the same mechanism driving semaglutide’s ~15% weight loss in STEP 1. Many GLP-1 medications act on one hormone pathway, so this arm is well-characterised; gastrointestinal tolerability is the dominant side-effect driver.
• GIP receptor: Adds insulinotropic and satiety effects that appear to blunt GLP-1-driven nausea while reinforcing satiety, and this arm may also support insulin sensitivity. This is the same arm that lifted tirzepatide above semaglutide in SURMOUNT-1 (~22.5% vs ~15%).
• Glucagon receptor: Increases basal energy expenditure and reduces hepatic fat. Glucagon also raises blood glucose; retatrutide’s balanced triple agonism is designed so the GLP-1 and GIP arms offset the glycemic impact of the glucagon arm, yielding a net glucose-neutral or glucose-lowering profile.

Compared to the obesity-pipeline alternatives, retatrutide is the only late-stage candidate that targets energy expenditure in addition to appetite. Tirzepatide is a dual agonist, while semaglutide works mainly through appetite and satiety, so triple-agonist designs may drive more weight loss and help some people lose weight when older weight loss drugs fall short. That broader mechanism is also why researchers ask how does retatrutide work to treat obesity and metabolic disease. Survodutide targets GLP-1 and glucagon (skipping GIP). CagriSema targets GLP-1 and amylin (skipping GIP and glucagon). Retatrutide is the mechanistic superset. For a receptor-by-receptor breakdown of what each arm controls and what trials measure, see the GLP-1, GIP and glucagon mechanism of action page.

Development Stage & TRIUMPH Programme

Retatrutide is in Phase 3 across the TRIUMPH programme, now broadened well beyond the original four lead indications — current Phase 3 work spans obesity, type 2 diabetes, knee osteoarthritis, moderate-severe obstructive sleep apnoea, chronic low back pain, cardiovascular and renal outcomes, and MASLD/MASH. Cumulative TRIUMPH enrolment exceeds 5,800. The pivotal TRIUMPH-1 obesity trial reported topline results on May 21, 2026 — 28.3% mean weight loss at 80 weeks on 12 mg (n=2,339), rising to 30.3% (~85.0 lb) at 104 weeks in a BMI ≥35 extension — joining the earlier TRIUMPH-4 readout (Dec 2025) and the TRANSCEND-T2D-1 readout (Mar 2026). Detailed TRIUMPH-1 results were presented at the 86th ADA Scientific Sessions in June 2026. TRIUMPH-2 and TRIUMPH-3 topline results were reported July 23, 2026 — full TRIUMPH-2 results are scheduled as an EASD late-breaker (Milan, September 30, 2026) — with remaining program work extending into 2027. Eli Lilly plans a U.S. BLA filing in Q1 2027; regulatory filing will follow the broader Phase 3 sequence.

Regulatory outlook: TRIUMPH-2 and TRIUMPH-3 topline results were reported July 23, 2026, with the full TRIUMPH-2 dataset scheduled as an EASD late-breaker on September 30, 2026. No U.S. application has yet been filed; Lilly plans a BLA filing in Q1 2027, and its Q2 2026 report (August 5) confirms the clinical data package is complete for global registrations in obesity, OSA, and knee osteoarthritis pain. For a running timeline, see the TRIUMPH trial tracker and the broader obesity drug pipeline timeline.

Manufacturing & filing outlook: Lilly’s July 23, 2026 release states that the company plans a U.S. BLA filing in Q1 2027 after completing the CMC package. Separately, Lilly’s $4.5 billion additional Indiana manufacturing investment supports its wider obesity and incretin pipeline rather than naming capacity for one molecule. Sources: Lilly July 23 release, manufacturing release.

Efficacy Data — TRIUMPH-1 Pivotal Phase 3 (May 2026)

The pivotal Phase 3 dataset is TRIUMPH-1 — a randomised, double-blind, placebo-controlled trial in 2,339 adults with obesity (BMI ≥30) or overweight (BMI ≥27 with comorbidity), excluding T2D. Baseline mean BMI 40.0; baseline weight 112.7 kg. Eli Lilly reported positive topline results on May 21, 2026. All three doses met the primary and key secondary endpoints.

On the 12 mg dose, 45.3% of participants achieved ≥30% weight loss and 65.3% reached a BMI under 30 — a magnitude often associated with bariatric surgery. A prespecified blinded extension in BMI ≥35 completers, maintained on 12 mg to the maximum tolerated dose, showed continued reduction to 30.3% mean weight loss at 104 weeks without an apparent plateau. Cardiometabolic improvements accompanied the weight loss, including a 24.1 cm waist-circumference reduction and favourable changes in non-HDL cholesterol, triglycerides, systolic blood pressure, and hs-CRP. Detailed results were presented at the 86th ADA Scientific Sessions in June 2026. Sources: Lilly investor release, TCTMD, AJMC.

Efficacy Data — Phase 2 NEJM Trial (Historical Context)

The Phase 2 dataset anchoring retatrutide’s pre-Phase-3 positioning is the 48-week randomised, double-blind, placebo-controlled trial published by Jastreboff and colleagues in the New England Journal of Medicine (June 2023). The trial enrolled 338 adults with obesity without type 2 diabetes and tested four retatrutide doses (1, 4, 8, 12 mg) against placebo.

Two features of the Phase 2 readout shaped retatrutide’s Phase 3 positioning. First, the dose-response was steep and orderly — every dose step produced meaningfully greater weight loss, which is a strong signal that the mechanism is active at the receptor level. Second, the 12 mg weight-loss curve had not plateaued at 48 weeks, implying longer dosing windows (as in TRIUMPH) could push efficacy higher still.

For cross-class context, semaglutide 2.4 mg produced ~15% weight loss at 68 weeks in STEP 1, and tirzepatide 15 mg produced ~22.5% at 72 weeks in SURMOUNT-1. Retatrutide’s 48-week number exceeds both, and the triple-agonist architecture provides a plausible mechanism. For a three-way breakdown, see Retatrutide vs Tirzepatide vs CagriSema.

Safety & Tolerability

Retatrutide’s Phase 2 safety profile was consistent with the GLP-1 class, layered with glucagon-related signals requiring further characterisation in Phase 3:

• Most common AEs: nausea, diarrhea, vomiting, constipation, decreased appetite — the standard GLP-1/GIP agonist profile, concentrated in dose-escalation phases.
• Heart rate: A modest dose-dependent increase in resting heart rate was observed, consistent with glucagon-receptor activation. The clinical significance is being monitored in TRIUMPH.
• Glycemic control: The balanced triple agonism produced neutral to favourable glycemic effects in Phase 2; HbA1c was not adversely affected.
• Hepatic fat: Retatrutide reduced hepatic fat content in Phase 2 substudy participants, consistent with the glucagon-arm mechanism.

No unexpected safety signals were reported in Phase 2. Long-term tolerability, cardiovascular outcomes, and discontinuation rates at commercial-intent doses are being characterised in TRIUMPH. For a dose-by-dose breakdown, see Phase 3 safety & adverse-event rates below. For a broader checklist of HbA1c, CMP, lipid, thyroid, and pancreatic-risk labs used before GLP-1-class protocols, see blood tests before starting GLP-1s and peptides.

Phase 3 Safety & Adverse-Event Rates

The Phase 2 dataset (Jastreboff et al., NEJM 2023) and the Phase 3 TRIUMPH-1 (May 2026), TRIUMPH-4 (December 2025), and TRANSCEND-T2D-1 (March 2026) topline readouts together form the most comprehensive safety dataset for retatrutide to date. The composite picture is consistent: gastrointestinal events dominate, severity is mostly mild-to-moderate, discontinuation runs in the single digits to low double digits at the highest dose, and titration design is the strongest tolerability lever.

TRIUMPH-1 dose-by-dose tolerability (May 21, 2026)

The TRIUMPH-1 dose-dependent discontinuation curve (4.1% / 6.9% / 11.3% vs 4.9% on placebo) is well below the 18.2% AE-driven discontinuation seen in the older TRIUMPH-4 obesity readout, validating the optimised 2 mg start with 4-week escalation steps adopted across the Phase 3 program. Dysesthesia at 12.5% sits between the TRIUMPH-4 high-dose signal and the lower TRANSCEND-T2D-1 incidence (2.3–4.5%). The new UTI signal is the most notable late-emerging observation and was quantified in Lilly’s release at 7.5–8.8% across retatrutide groups versus 5.3% on placebo. Detailed results were presented at the 86th ADA Scientific Sessions in June 2026.

TRIUMPH-1 vs TRIUMPH-4 — tolerability at the 12 mg dose

The clearest read on retatrutide’s evolving tolerability is the side-by-side comparison of the two high-dose obesity readouts. The pivotal TRIUMPH-1 obesity cohort showed improved tolerability versus the older TRIUMPH-4 (obesity plus knee osteoarthritis) figures on both the dysesthesia signal and AE-driven discontinuation.

In Lilly's topline reports, dysesthesia at the 12 mg dose was 12.5% in TRIUMPH-1 and 20.9% in TRIUMPH-4; adverse-event discontinuation was 11.3% and 18.2%, respectively. Differences between separate trials should not be interpreted as a head-to-head safety comparison. Sources: Lilly TRIUMPH-1 release, Lilly TRIUMPH-4 release.

Phase 2 GI rates by dose & titration design

Key finding: The 8 mg rapid-start cohort produced higher nausea (~60%) than the 12 mg slow-titration cohort (45.8%), even though the final dose was lower. Nausea incidence is dose dependent, but titration schedule is the primary tolerability lever — starting at 2 mg rather than 4 mg before escalation reduced nausea incidence by 30–50%. Phase 2 used four-week dose-escalation steps to allow adaptation during the treatment period (Jastreboff et al., NEJM 2023, Table 3).

Cross-class comparison — retatrutide vs tirzepatide vs semaglutide

Retatrutide’s GI side-effect rates sit in the same general range as tirzepatide and semaglutide, but peak nausea can run modestly higher at the most aggressive dose levels. Per unit of weight reduction (~24% at 12 mg vs ~22.5% tirzepatide, ~15% semaglutide), the tolerability profiles are broadly comparable. Discontinuation rates fall in a comparable band across the class.

Severity stratification

Phase 2 trial reports describe retatrutide adverse events as predominantly mild-to-moderate, with severe events under 5% per individual AE category. Overall AE-driven discontinuation across active dose groups was approximately 6–8% in Phase 2 and 2.2–5.1% across TRANSCEND-T2D-1 dose arms.

GI symptom timeline — onset, peak, resolution

Trial narrative reports describe a consistent onset/peak/resolution pattern for the GI category, with most events concentrated in the dose-escalation window.

Severe abdominal pain was reported in a small subset of Phase 2 participants at higher doses. Trial reports describe pain that persists beyond 48 hours or is accompanied by persistent vomiting as a flag for further investigation, with acute pancreatitis included in the differential and pancreatic enzymes (serum amylase, lipase) measured to rule out acute pancreatic disorders. No confirmed pancreatitis signal has been reported in Phase 2 or Phase 3 readouts to date, but the GLP-1 class warning applies by mechanism.

TRIUMPH-4 Phase 3 update (December 2025)

Eli Lilly reported topline results from the TRIUMPH-4 Phase 3 trial on December 11, 2025. TRIUMPH-4 evaluated retatrutide in adults with obesity and knee osteoarthritis across a larger and more diverse population than Phase 2, using the optimised slow-titration protocol informed by Phase 2 dose-finding. Topline results confirmed that retatrutide met its primary efficacy endpoint. Lilly’s announcement indicated the safety profile was broadly consistent with Phase 2 — gastrointestinal events remained the most common adverse events, no new safety signals were identified, and discontinuation rates were comparable to Phase 2. Dysesthesia — tingling/numbness — was reported at the high dose at frequencies higher than placebo (TRIUMPH-4 high-dose stat-chip approximation: ~20.9%). Full TRIUMPH-4 safety tables are expected in a peer-reviewed publication in 2026.

TRANSCEND-T2D-1 Phase 3 readout (March 2026)

On March 19, 2026, Eli Lilly announced topline results from TRANSCEND-T2D-1 — the first Phase 3 trial evaluating retatrutide in type 2 diabetes. The 40-week, placebo-controlled study randomised 537 participants to retatrutide 4 mg, 9 mg, or 12 mg (starting at 2 mg with four-week dose escalation) or placebo.

Notably, nausea rates in TRANSCEND-T2D-1 (16.4–26.5%) ran substantially lower than in the Phase 2 trial (up to 45.8% at 12 mg), likely reflecting the optimised 2 mg initiation and slower titration protocol adopted for Phase 3. Dysesthesia — the tingling/numbness signal first flagged in TRIUMPH-4 — occurred in 2.3–4.5% of retatrutide-treated participants and was described as generally mild, resolving during treatment. Discontinuation rates due to adverse events were low across all doses (2.2–5.1%). Detailed TRANSCEND-T2D-1 safety results were presented at the American Diabetes Association Scientific Sessions in June 2026.

Heart rate & cardiovascular signals

The Phase 2 trial identified small, dose-dependent increases in resting heart rate among retatrutide-treated participants. Mean heart rate increases of approximately 2–4 beats per minute (bpm) were observed at the higher dose levels, consistent with the well-documented class effect of GLP-1 receptor agonists. Semaglutide and tirzepatide both produce similar modest heart rate elevations of 1–4 bpm in their respective Phase 3 programmes. The mechanism is believed to involve GLP-1 receptor-mediated effects on the sinoatrial node and sympathetic nervous system modulation.

No major adverse cardiovascular events (MACE) were identified as attributable to retatrutide in the Phase 2 trial, which was not powered to detect rare cardiovascular events. TRIUMPH-3 enrolled people with established cardiovascular disease, but Lilly’s July 23 topline release reported obesity endpoints and did not establish a MACE benefit.

Class-wide safety considerations

Class-wide considerations reference FDA labels for tirzepatide (Mounjaro/Zepbound) and semaglutide (Wegovy/Ozempic). Retatrutide entries reflect investigational status; class warnings apply by mechanism. Combining GLP-1 receptor agonists with insulin or sulfonylureas increases the risk of hypoglycemia — a documented class effect that applies to retatrutide by mechanism. Trial protocols typically reduce concomitant insulin or sulfonylurea doses when GLP-1 agonists are added.

How It Compares — Retatrutide vs Tirzepatide vs CagriSema

Retatrutide sits at the mechanistic top of the obesity pipeline. Tirzepatide (Eli Lilly, approved as Mounjaro and Zepbound) is a dual GLP-1/GIP agonist. CagriSema (Novo Nordisk, NDA filed December 2025) is a GLP-1/amylin co-formulation. Retatrutide adds a glucagon arm that neither of those candidates has, which is the source of its weight-loss ceiling advantage in cross-trial comparison.

On efficacy, retatrutide’s Phase 3 TRIUMPH-1 12 mg result (28.3% at 80 weeks; 30.3% at 104 weeks in the BMI ≥35 extension) exceeds tirzepatide 15 mg in SURMOUNT-1 (~22.5% at 72 weeks) and CagriSema in REDEFINE 1 (~22.7% at 68 weeks). Timeline position is inverted: CagriSema is closest to market (FDA decision expected ~October 2026), tirzepatide is already approved, and retatrutide is still working through TRIUMPH. For a full comparative breakdown, see retatrutide vs tirzepatide vs CagriSema, and for orforglipron-specific context, see retatrutide vs orforglipron.

Research Use Notes

Remy Peptides publishes peptide research; it supplies no compounds. The archived batch record for the HPLC-verified retatrutide pen documents Retatrutide Pen 30 mg, 300 clicks at 0.1 mg per click, 99.262% HPLC purity, Janoshik Analytical Batch RETP002. Reference the COA library for batch documents. For reconstitution and handling, see the bacteriostatic water guide and the reconstitution calculator.

Retatrutide is not approved for human therapeutic use in any territory. The batch records published here document material for in-vitro laboratory research only. For regional research context, see the Dubai research guide and Retatrutide UAE availability page.

Everything documented here is for in-vitro laboratory research only. Not for human or veterinary use.

July 23, 2026 TRIUMPH-2 and TRIUMPH-3 update

Eli Lilly reported topline results from two additional Phase 3 retatrutide trials on July 23, 2026. In TRIUMPH-2 (1,152 adults with obesity or overweight and type 2 diabetes; 80 weeks), the company reported mean weight reductions of 12.7% at 4 mg, 19.1% at 9 mg, and 20.8% at 12 mg, with A1C reductions up to 1.6 percentage points. In TRIUMPH-3 (1,949 adults with severe obesity and established cardiovascular disease; 80 weeks), mean weight reduction reached 21.6% at 9 mg and 22.6% at 12 mg versus 3.2% on placebo. These are company-reported topline findings, not a head-to-head comparison; full TRIUMPH-2 results are scheduled as a late-breaker at EASD in Milan on September 30, 2026, with TRIUMPH-3 to follow at a future meeting.

Lilly also stated that it plans a U.S. Biologics License Application in Q1 2027 after completing the chemistry, manufacturing, and controls package; the company's Q2 2026 report (August 5) states the clinical data package is complete to support global registrations in obesity, obstructive sleep apnea, and knee osteoarthritis pain. Retatrutide remains investigational and no application has yet been approved. Primary source: Eli Lilly, July 23, 2026.