Research guide
Retatrutide
Retatrutide (LY3437943) is a 39-amino-acid synthetic triple hormone receptor agonist peptide developed by Eli Lilly, engineered to activate three metabolic receptors simultaneously: glucagon-like peptide-1 (GLP-1), glucose-dependent insulinotropic polypeptide (GIP), and glucagon (GCG). The triple mechanism targets complementary pathways for appetite, glucose, and energy homeostasis. Modified with a C20 fatty-acid side chain for approximately 6-day half-life, enabling once-weekly subcutaneous dosing. Currently investigational (Phase 3 trials ongoing as of June 2026); not FDA-approved. Supplied for research use in preclinical and clinical research settings only.
What the research shows
Phase 3 TRIUMPH-1 trial: 28.3% mean body weight reduction at 12 mg dose over 80 weeks; 45.3% of participants achieved ≥30% weight loss, matching bariatric surgery outcomes
positive · Eli Lilly Press Release & TRIUMPH-1 Phase 3 Data ↗
TRIUMPH-4 (obesity + knee OA): 28.7% weight loss and substantial osteoarthritis pain relief; improved blood pressure and lipid markers
positive · Lilly TRIUMPH-4 Phase 3 Results ↗
Phase 2a NASH trial: Triple agonism shows improvement in metabolic dysfunction-associated steatotic liver disease with cardiometabolic benefits
positive · Nature Medicine Phase 2a NASH Trial ↗
Structural analysis: 8.9-fold greater potency at GIPR; 0.3-fold (3x less potent) at GCGR; 0.4-fold (2.5x less potent) at GLP-1R vs natural ligands
neutral · PMC Structural Insights Article ↗
Most common adverse events at 12 mg: nausea (42.4%), diarrhea (32%), constipation (26.1%), vomiting (25.3%); generally mild, dose-dependent, infrequently led to discontinuation
mixed · TRIUMPH-1 Phase 3 Safety Data ↗
Among participants with prediabetes: 72% returned to normoglycemia; clear improvements in blood pressure and fasting glucose
positive · Eli Lilly TRIUMPH Phase 3 Efficacy Data ↗
Phase 2 obesity trial: Average weight reduction 24.2% at 12 mg dose after 48 weeks; outperforms tirzepatide 20.2% and semaglutide 13.7%
positive · Nature Medicine Phase 2 Data & Comparative Analysis ↗
What experts say — both sides
Results show clear improvements in cardiometabolic health measures alongside 28.3% weight reduction; retatrutide could be 'a highly impactful future tool to treat obesity and transform the health trajectory' of patients.
Retatrutide topline results suggest weight losses approaching bariatric surgery range historically achievable, which is 'striking' and unprecedented for pharmacotherapy.
Very encouraging topline findings, but direct cross-trial comparisons should be made with caution due to different populations, eligibility criteria, and trial designs.
Retatrutide demonstrates superior triple agonism efficacy and safety profile across obesity, NASH, and cardiometabolic outcomes; systematic review confirms game-changing potential in obesity pharmacotherapy.
Safety & legal status
Retatrutide (LY3437943) is investigational, not FDA-approved as of June 2026. Phase 3 TRIUMPH trials ongoing; FDA submission expected Q4 2026 or Q1 2027; approval projected late 2027 or 2028. For research use: supplied explicitly for in vitro laboratory and preclinical research only, not human consumption. Based on animal studies and Phase 2/3 data, likely to carry FDA boxed warning for thyroid C-cell tumors (class effect with GLP-1/GIP agonists). Common adverse events: nausea (42.4%), diarrhea (32%), constipation (26.1%), vomiting (25.3%); generally mild. Animal reproduction studies show skeletal/visceral malformation risk. No compounding restrictions yet exist (not approved). Research-use retatrutide legal for laboratory purchase/possession for experimental research only pending future FDA approval status.
Research use only. Nothing here is medical or dosing advice.
Retatrutide — FAQ
What is retatrutide and how does it differ from tirzepatide and semaglutide?
Retatrutide activates three receptors (GLP-1+GIP+GCG) vs tirzepatide's two and semaglutide's one, providing triple synergistic metabolic regulation for superior weight loss and blood sugar control.
How much weight loss does retatrutide achieve?
Phase 3 trials show 28.3% mean weight loss (up to 30.3% at highest dose), the highest efficacy among GLP-1 class peptides and comparable to bariatric surgery outcomes.
When will retatrutide be FDA approved?
Retatrutide is investigational; Phase 3 trials ongoing (June 2026). FDA submission expected late 2026/early 2027; approval projected late 2027 or 2028.
What are retatrutide's side effects?
Most common: nausea (42.4%), diarrhea (32%), constipation (26.1%), vomiting (25.3%); generally mild to moderate and dose-dependent.
Is retatrutide better than tirzepatide for weight loss?
Phase 3 data shows retatrutide achieves greater weight loss (28.3% vs tirzepatide's 20.2%), but direct RCT comparison is pending; both represent major advances.
See which vendors pass our audit for Retatrutide.
Why trust this comparison
- Every vendor is scored from real evidence on four public, weighted axes — before we know any margins.
- Purity claims are cross-checked against named third-party labs (MZ Biolabs, Finnrick, Janoshik). Claim-only purity is marked as such.
- The scoring code can't read which vendor pays us — the editorial-commerce firewall is enforced in software.
- We disclose the 20% / 10% Alpha Pro commission on every page, above the first link.
Vendors out-rank our own partner: Peptide Partners (9.0) and Protide Health (8.9) and Ascension Peptides (8.8) both score above Alpha Pro (8.6). We left it that way.