Retatrutide

Overview

GIP/GLP-1/glucagon triple receptor agonist showing superior weight loss.

Reported benefits

Enhanced weight loss beyond dual agonists, metabolic improvement

Mechanism of action

Retatrutide (LY3437943) is a 31-aa acylated peptide triagonist with C18 fatty-diacid chain via mini-PEG linker enabling once-weekly dosing. Three receptor pathways: (1) GIP receptor agonism -- augments glucose-dependent insulin secretion, reduces food intake via hypothalamic GIPR, activates brown adipose tissue (BAT) thermogenesis; the primary mechanism beyond dual agonists. (2) GLP-1 receptor agonism -- suppresses appetite via arcuate nucleus POMC, delays gastric emptying, glucose-dependent insulin release, reduces hepatic glucose output. (3) Glucagon receptor agonism -- hepatic glucose reduction, additional energy expenditure via BAT, PCSK9 protease degradation leading to ~20% LDL-C reduction unique vs semaglutide/tirzepatide. No weight-loss plateau observed through 80+ weeks.

Research & clinical studies

TRIUMPH PROGRAM Phase 3 (8 pivotal trials + 10,000-patient CVOT): TRIUMPH-4 (Dec 2025, 68 weeks, knee OA population): 28.7% weight loss (12 mg), WOMAC pain -75.8%, >12.5% patients free from knee pain, LDL-C -20%, discontinuation 18.2% (12 mg). TRANSCEND-T2D-1 (Mar 2026, 40 weeks, T2DM): HbA1c -2.0%, weight loss 16.8% (12 mg), all endpoints met. TRIUMPH-1 (May 21 2026, n=2339, general obesity, 80 weeks): 4 mg -17.6%, 9 mg -23.7%, 12 mg -25.0% (avg 70.3 lbs), placebo -3.9%. 65.3% on 12 mg crossed BMI <30. ~50% achieved >=30% weight loss. 104-week extension (BMI>=35): 30.3% (avg 85 lbs). LDL-C -20%. No plateau through 80 weeks. Pending: TRIUMPH-2, 3, 5-8. Full data at ADA June 2026. FDA NDA submission anticipated Q3-Q4 2026.

Protocols & dosing

Typical dosage: Clinical trials (weekly).

TRIUMPH Phase 3 titration (reference): Week 1-4: 2 mg weekly. Week 5-8: 4 mg. Week 9-12: 9 mg. Week 13+: 12 mg (max). Titrate every 4 weeks as tolerated. Auto-injector pen subQ. Anti-emetic: ondansetron 4 mg oral 30-60 min pre-injection during escalation. Low-fat meals on injection days. Monitor: fasting glucose, HbA1c if T2DM, LDL-C (expect improvement), lipase/amylase. NOT FDA-APPROVED -- investigational reference only.

Popular combinations

DO NOT COMBINE with other GLP-1/GIP/glucagon agonists. ESSENTIAL ADJUNCTS: Resistance training 3-4x/week (mandatory), protein 1.6-2.2 g/kg/day, creatine 3-5 g daily. BONE HEALTH: Calcium 1000-1200 mg + Vitamin D 2000-4000 IU with rapid weight loss. HAIR LOSS MITIGATION: adequate protein, iron, zinc, biotin. LDL-C reduction expected (~20%) -- may reduce statin need.

FDA & legal status

Retatrutide is not currently FDA-approved for any indication. It is generally classified as a research compound. Regulatory status varies by country.

Vendor information

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Side effects & safety

Reported side effects: Clinical trial phase

INVESTIGATIONAL -- not FDA-approved anywhere as of May 2026. TRIUMPH-1 (12 mg): nausea 42.4%, diarrhea 32.0%, constipation 26.1%, vomiting 25.3%. UNIQUE SIGNAL: dysesthesia (abnormal sensory perceptions) ~10% on highest doses (up to 20.9% in TRIUMPH-4), generally mild/transient, majority resolved during treatment. UTIs ~10% on highest doses. DISCONTINUATION: 4.1% (4 mg), 6.9% (9 mg), 11.3% (12 mg) vs 4.9% placebo -- higher than tirzepatide SURMOUNT-1. CLASS RISKS: thyroid C-cell tumor (contraindicated MTC/MEN2), pancreatitis, cholelithiasis, gastroparesis.

Community experiences

TRIUMPH-1 (May 2026) delivered bariatric-surgery-equivalent outcomes: 30.3% at 104 weeks approaches Roux-en-Y gastric bypass (~30-35% EWL). Three differentiators: (1) LDL-C -20% unique in incretin class via glucagon-receptor-driven PCSK9 degradation; (2) Continuous weight loss to 80+ weeks without plateau; (3) Osteoarthritis pain data expands patient population. CONCERNS: dysesthesia signal needs peer-reviewed characterization; GI burden higher than tirzepatide; discontinuation 11.3% (12 mg) vs tirzepatide 4.3%. FDA NDA filing expected end of 2026; market availability estimated 2027.

References

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