Quick Facts: Retatrutide at a Glance
Snapshot of the most-cited retatrutide research figures, with primary source for each. Use this table as a quick reference; full context and additional cohort breakdowns appear in the sections below.
| Fact | Value | Primary source |
|---|---|---|
| INN / Research code | Retatrutide / LY3437943 | Eli Lilly pipeline disclosure |
| Developer | Eli Lilly & Company | investor.lilly.com |
| Receptor targets | GLP-1R + GIPR + GcgR (triple agonist) | Coskun et al., Nat Metab 2022 |
| Drug class | Triple GLP-1 / GIP / Glucagon receptor agonist | Coskun et al., Nat Metab 2022 |
| Estimated half-life | ~6 days (supports once-weekly dosing) | Coskun et al., Nat Metab 2022 (Phase 1 PK) |
| Phase 2 publication | NEJM, 28 June 2023 | Jastreboff et al., NEJM 2023 |
| Phase 2 trial size | 338 adults | NEJM 2023 / NCT04881760 |
| Phase 2 duration | 48 weeks (primary endpoint at 24 weeks) | NEJM 2023 |
| Peak mean weight loss | 24.2% at 12mg/week, 48 weeks | NEJM 2023, Jastreboff et al. |
| Placebo-adjusted reduction (12mg) | ~22.1% | NEJM 2023 |
| Lowest-dose response (1mg) | 8.7% mean weight loss | NEJM 2023 |
| Nausea rate (12mg cohort) | ~42% | NEJM 2023 safety data |
| AE-driven discontinuation (12mg) | ~6.4% | NEJM 2023 safety data |
| Phase 3 programme name | TRIUMPH | Eli Lilly pipeline |
| TRIUMPH-1 result (12mg, 80 wk) | 28.3% mean weight loss (vs 2.2% placebo); reported 21 May 2026 | Eli Lilly / Pharmaceutical Journal |
| TRIUMPH-1 enrolment | 2,339 adults (4mg / 9mg / 12mg / placebo) | Eli Lilly, 21 May 2026 |
| Largest TRIUMPH trial | SYNERGY-OUTCOMES, ~17,000+ enrolment | NCT06077864 |
| Remaining Phase 3 readouts | TRIUMPH-2/-3 and SYNERGY-OUTCOMES through 2026–2028 | Eli Lilly investor guidance |
| Approval status (Australia, 2026) | Not approved as a therapeutic; research-grade supply for laboratory use only | TGA register |
Definitions used in this page · Mean weight loss = arithmetic mean percentage reduction in body weight from baseline at the trial primary endpoint. · Placebo-adjusted = treatment arm minus placebo arm at the same timepoint. · AE-driven discontinuation = trial participants who withdrew due to adverse events, distinct from all-cause discontinuation. · Cohort = dose arm within a single trial. Cross-trial comparison ≠ head-to-head trial.
Phase 2 Trial: The Numbers
The pivotal retatrutide Phase 2 trial (NEJM, June 2023, Jastreboff et al., NCT04881760) is the most-cited single source for retatrutide research statistics through to the readout of the Phase 3 TRIUMPH programme. Top-line trial numbers:
| Parameter | Value |
|---|---|
| Trial design | Phase 2, randomised, double-blind, placebo-controlled |
| Trial duration | 48 weeks (primary endpoint) |
| Total enrolment | 338 adults |
| Population | BMI ≥ 30, or BMI ≥ 27 with at least one weight-related comorbidity, without type 2 diabetes |
| Geographic distribution | Multi-centre, primarily United States sites |
| Dose cohorts | Six: placebo, 1mg, 4mg (slow), 4mg (fast), 8mg (fast), 12mg (fast), all weekly subcutaneous |
| Titration schedule | Phase 2 used compressed 2–4 week dose escalation steps |
Weight-Loss Endpoints by Dose Cohort (Phase 2, 48 weeks)
Mean body-weight reduction from baseline at the 48-week primary endpoint:
| Dose cohort | Mean weight loss | Placebo-adjusted reduction |
|---|---|---|
| Placebo | 2.1% | - |
| 1mg/week | 8.7% | ~6.6% |
| 4mg/week (slow titration) | 12.9% | ~10.8% |
| 4mg/week (fast titration) | 17.3% | ~15.2% |
| 8mg/week | 22.8% | ~20.7% |
| 12mg/week | 24.2% | ~22.1% |
Secondary endpoint magnitudes at the 12mg cohort: 41% mean reduction in fasting insulin; 43% mean reduction in triglycerides; 18.5 cm mean reduction in waist circumference; meaningful reduction in liver fat fraction on MRI in a measured subset.
By comparison: STEP 1 semaglutide reported 14.9% mean weight loss at 68 weeks at the 2.4mg/week dose; SURMOUNT-1 tirzepatide reported 20.9% at 72 weeks at the 15mg/week dose. Retatrutide's 24.2% was achieved 20–24 weeks faster than either comparator's trial endpoint.
Phase 3 TRIUMPH-1 Results (Reported 21 May 2026)
On 21 May 2026, Eli Lilly reported topline results from TRIUMPH-1, the pivotal Phase 3 obesity trial, the first Phase 3 efficacy readout in the retatrutide programme. The trial randomised 2,339 adults with obesity (or overweight with a weight-related comorbidity) and without type 2 diabetes to retatrutide 4mg, 9mg, or 12mg weekly (titrated upward from 2mg in four-weekly steps) or placebo. The primary endpoint was mean percentage change in body weight at 80 weeks.
| Dose cohort | Mean weight loss at 80 weeks | AE-driven discontinuation |
|---|---|---|
| Placebo | 2.2% | ~4.9% |
| 4mg/week | 19.0% | ~4.1% |
| 9mg/week | 25.9% | ~6.9% |
| 12mg/week | 28.3% | ~11.3% |
In a higher-BMI subgroup (n≈532) escalated to the maximum tolerated dose, mean weight reduction reached up to ~30% by week 104. The Phase 3 result confirms that the dose-response gradient observed in Phase 2 held at scale across a larger population and a longer 80-week endpoint. AE-driven discontinuation rose with dose, consistent with the dose-dependent gastrointestinal profile of the GLP-1 class.
These figures are drawn from Eli Lilly's 21 May 2026 topline disclosure and contemporaneous reporting in the Pharmaceutical Journal. Full peer-reviewed publication and additional TRIUMPH readouts are pending. Cross-trial comparisons with semaglutide and tirzepatide remain observational, not head-to-head. Retatrutide is supplied by RetaLABS for laboratory research use only and is not approved as a therapeutic in Australia.
Adverse Event Rates by Dose Cohort
Phase 2 adverse event rates at the highest dose cohort (12mg) summarised:
| Event | Rate at 12mg | Rate at placebo |
|---|---|---|
| Nausea | ~42% | ~13% |
| Vomiting | ~20% | ~3% |
| Diarrhoea | ~18% | ~13% |
| Constipation | ~14% | ~7% |
| Decreased appetite | Majority of subjects | ~10% |
| Injection site reactions | ~8% | ~4% |
| Serious adverse events | ~6% | ~5% |
GI events were dose-dependent and concentrated in the titration window. No cases of pancreatitis, thyroid C-cell tumours, or severe hypoglycaemia were reported in the Phase 2 cohort at any dose. See Retatrutide Side Effects (Australia) for protocol-design implications and the broader GLP-1 Side Effects Cross-Compound Profile for class-level context.
Discontinuation Statistics
Discontinuation rates from the Phase 2 trial:
| Cohort | AE-driven discontinuation | All-cause discontinuation |
|---|---|---|
| Placebo | ~1.4% | ~16% |
| 1mg | ~4.6% | ~17% |
| 4mg (slow) | ~4.5% | ~16% |
| 4mg (fast) | ~4.7% | ~16% |
| 8mg | ~6.3% | ~21% |
| 12mg | ~6.4% | ~22% |
The compressed titration schedule (2-week step increments in some cohorts) drove a higher peak AE rate during the early weeks. Most discontinuations were concentrated in weeks 1–12.
Phase 3 TRIUMPH Programme: Enrollment Numbers
Eli Lilly's Phase 3 TRIUMPH programme is the global Phase 3 development plan for retatrutide. Enrolment numbers and status as of early 2026:
| Trial | NCT identifier | Target enrolment | Status (Q2 2026) |
|---|---|---|---|
| TRIUMPH-1 (obesity) | NCT05882045 | 2,339 randomised | Primary results reported 21 May 2026 (see section above) |
| TRIUMPH-2 (obesity with sleep apnoea) | NCT05882049 | ~675 | Active follow-up |
| TRIUMPH-3 (obesity + cardiovascular disease) | NCT05882077 | ~1,800 | Active enrolment in 2026; Australian sites including University of Sydney Boden Initiative |
| TRIUMPH-4 (obesity in adolescents) | NCT05989711 | ~600 | Active enrolment |
| SYNERGY-OUTCOMES (cardiovascular outcomes MACE) | NCT06077864 | ~17,000+ | Active multi-centre enrolment; multiple Australian cardiology sites |
| TRIUMPH-NAFLD (MASH liver disease) | NCT06324877 | ~700 | Active enrolment |
TRIUMPH-1 primary results were reported on 21 May 2026 (see the TRIUMPH-1 results section above). Remaining readouts, TRIUMPH-3 and the other sub-trials, are anticipated through 2026 to mid-2027, while SYNERGY-OUTCOMES (the cardiovascular outcomes trial) follows a longer timeline through 2028. Australian enrolment is most concentrated in TRIUMPH-3 (University of Sydney) and SYNERGY-OUTCOMES (cardiology sites nationally). NCT identifiers above can be verified at clinicaltrials.gov; final enrolment numbers may differ from registered targets.
Regulatory Approval Status by Jurisdiction (2026)
As of June 2026, retatrutide (LY3437943) has not received regulatory approval as a therapeutic in any jurisdiction. TRIUMPH-1, the first Phase 3 efficacy readout, was reported on 21 May 2026. The full Phase 3 programme — including TRIUMPH-3, TRIUMPH-NAFLD, and SYNERGY-OUTCOMES — remains ongoing through 2027–2028. A regulatory filing (NDA/BLA with the FDA, MAA with the EMA) would follow compilation of the complete clinical data package after Phase 3 completion.
| Jurisdiction | Regulatory body | Status (June 2026) | Notes |
|---|---|---|---|
| United States | FDA | Not approved — investigational | IND active; Phase 3 ongoing. NDA/BLA filing depends on full TRIUMPH programme completion. TRIUMPH-1 topline data reported May 2026; SYNERGY-OUTCOMES cardiovascular outcomes data expected through 2028. |
| European Union | EMA | Not approved — investigational | No MAA (Marketing Authorisation Application) filed or announced as of June 2026. Filing would follow Phase 3 completion. |
| Australia | TGA | Not on ARTG — not approved as a therapeutic | TGA approval of novel therapeutics typically follows FDA or EMA approval by 12–24 months via the ARTG registration pathway. Research-grade supply for laboratory use is a separate regulatory category from therapeutic goods; see Research Peptides Legal Framework in Australia. |
| United Kingdom | MHRA | Not approved — investigational | Post-Brexit UK requires an independent MHRA review. No application announced as of June 2026. |
| Canada | Health Canada | Not approved — investigational | No NDS (New Drug Submission) filing announced as of June 2026. |
| New Zealand | Medsafe | Not approved — investigational | Medsafe reviews for novel compounds often follow TGA decisions. No application announced. |
| Japan | PMDA | Not approved — investigational | PMDA typically requires bridging studies with Japanese-population data for novel therapeutics. |
| China | NMPA | Not approved — investigational | NMPA generally requires local Phase 3 bridging data. No filing announced as of June 2026. |
Scope note: This table covers the status of retatrutide as an approved therapeutic good. RetaLABS supplies retatrutide as a research-grade compound for laboratory use only — a distinct regulatory category from approved pharmaceutical formulations. For the Australian framework governing research-grade peptide supply, see the Research Peptides Legal Status guide. This page is not legal advice.
Class Comparison: The Numbers Side-by-Side
Cross-trial comparison across the three GLP-1 receptor agonists in current clinical development. These are separate trials with different populations, durations, and designs, not a head-to-head study, so direct ranking requires caution.
| Metric | Semaglutide (STEP 1) | Tirzepatide (SURMOUNT-1) | Retatrutide (Phase 2) |
|---|---|---|---|
| Trial enrolment | 1,961 | 2,539 | 338 |
| Trial duration | 68 weeks | 72 weeks | 48 weeks |
| Highest dose | 2.4mg/week | 15mg/week | 12mg/week |
| Mean weight loss at highest dose | 14.9% | 20.9% | 24.2% |
| Nausea rate at highest dose | ~44% | ~29% | ~42% |
| AE-driven discontinuation at highest dose | ~4.5% | ~4.3% | ~6.4% |
| Receptor targets | GLP-1R only | GLP-1R + GIPR | GLP-1R + GIPR + GcgR |
| Phase 3 status | Complete; therapeutic approval in multiple jurisdictions | Complete; therapeutic approval in multiple jurisdictions | TRIUMPH-1 reported 21 May 2026 (28.3% at 80 wk, 12mg); programme ongoing |
For mechanistic context behind these numbers, see the Retatrutide Research Guide and the GLP-1 Peptides Comparison Guide.