BPC-157: The Good, The Bad & The Research

Retatrutide (LY3437943) is an investigational peptide compound developed by Eli Lilly. It is a triple receptor agonist — simultaneously activating three metabolic hormone receptors: GLP-1 (glucagon-like peptide-1), GIP (glucose-dependent insulinotropic polypeptide), and the glucagon receptor.

No currently approved drug targets all three receptors at once. This multi-receptor mechanism is what makes Retatrutide one of the most discussed and researched compounds in metabolic science today.

GLP-1 Receptor: Suppresses appetite, stimulates insulin secretion in a glucose-dependent manner, and slows gastric emptying. This is the same receptor targeted by semaglutide (Ozempic/Wegovy).

GIP Receptor: Enhances fat metabolism, potentiates insulin secretion, and boosts the effectiveness of GLP-1 signaling. This receptor is also targeted by tirzepatide (Mounjaro/Zepbound).

Glucagon Receptor: Drives thermogenesis and energy expenditure — increasing calorie burn and broadening the metabolic reach of the compound beyond appetite suppression alone. This is the key differentiator that sets Retatrutide apart from all existing approved therapies.

In the Phase 2 trial published in the New England Journal of Medicine in June 2023, participants receiving the highest dose (12 mg weekly) achieved a mean body weight reduction of 24.2% — approximately 57.8 lbs (26.2 kg) — over 48 weeks. This surpassed results seen with semaglutide (~15-17%) and tirzepatide (~20-22%) in comparable trial settings.

In December 2025, Eli Lilly announced the first successful Phase 3 readout from the TRIUMPH-4 trial. Participants on the highest dose achieved an average weight loss of 28.7% — approximately 71.2 lbs — over 68 weeks. This represents the highest weight loss ever recorded in a Phase 3 obesity trial, rivaling outcomes typically associated with bariatric surgery.

Source: Jastreboff AM et al. NEJM 2023;389:514-526. doi:10.1056/NEJMoa2301972 | Eli Lilly TRIUMPH-4 Press Release, December 2025

Non-alcoholic fatty liver disease (NAFLD) affects an estimated 42% of adults in the United States — and over 60% of adults over the age of 50. Most do not know they have it.

In a Phase 2 sub-study examining participants with NAFLD, Retatrutide produced an 82-86% mean reduction in liver fat content over 24 weeks as measured by MRI-PDFF. In the highest dose group, 93% of participants achieved complete normalization of liver fat — dropping below the 5% threshold considered normal.

Researchers believe Retatrutide addresses NAFLD at its root causes — reducing caloric intake, increasing energy expenditure, and improving how the body handles glucose and fat.

Source: Loomba R et al. NEJM Evidence 2023. doi:10.1056/EVIDoa2200291

In Phase 2 data, 72% of prediabetic participants reverted to normal blood sugar levels — compared to just 22% in the placebo group. This is a landmark finding suggesting Retatrutide may have significant implications for the prevention and reversal of type 2 diabetes onset.

TRIUMPH-4 Phase 3 data confirmed meaningful cardiovascular improvements including:

— Systolic blood pressure dropped approximately 14 mmHg — double the effect of many blood pressure medications
— 41% of participants stopped at least one blood pressure medication entirely
— Triglycerides reduced up to 36%
— Significant improvements in non-HDL cholesterol and lipid markers
— Superior HbA1c reduction compared to dulaglutide (Trulicity)

Source: Rosenstock J et al. NEJM 2023;389:1079-1091. doi:10.1056/NEJMoa2306607 | Eli Lilly TRIUMPH-4 Press Release, December 2025

The Phase 2 and Phase 3 data document a clear side effect profile. These are generally mild to moderate and most pronounced during dose escalation phases:

— Nausea — the most commonly reported side effect, dose-dependent
— Slowing of the digestive tract (gastroparesis-like effects) — a mechanism-driven consequence of GLP-1 receptor activation
— Vomiting — linked with nausea, typically decreases over time
— Digestive upset and diarrhea — particularly during dose escalation
— Decreased appetite — largely an intended mechanism-driven effect
— Injection site reactions — mild local redness or discomfort

Gastrointestinal side effects were generally mild and infrequently led to trial discontinuation according to TRIUMPH-4 reporting.

Retatrutide has not completed all Phase 3 trials. Long-term safety data — at 2, 5, and 10-year timeframes — does not yet exist. We do not fully understand:

— The full long-term cardiovascular outcomes profile
— The effects of sustained triple receptor activation over many years
— Complete drug interaction profiles
— Real-world performance outside controlled trial conditions
— Long-term effects on bone density, muscle mass, and other markers

The Phase 3 data is compelling. But compelling is not complete. Transparency demands we acknowledge what the research has not yet answered.

Retatrutide is currently in the most extensive Phase 3 development program for any metabolic compound in history. The TRIUMPH program includes:

— TRIUMPH-1: Obesity without type 2 diabetes
— TRIUMPH-2: Obesity with type 2 diabetes
— TRIUMPH-3: Cardiovascular disease outcomes
— TRIUMPH-4: Obesity and knee osteoarthritis — Phase 3 results confirmed December 2025
— TRIUMPH-Outcomes: Cardiovascular and kidney outcomes
— Additional trials: obstructive sleep apnea and MASLD/NAFLD

Seven additional Phase 3 readouts are expected throughout 2026. FDA NDA filing is anticipated Q4 2026 — Q1 2027.

How It Compares:
— Semaglutide (Ozempic/Wegovy) — GLP-1 only — ~15-17% weight loss
— Tirzepatide (Mounjaro/Zepbound) — GLP-1 + GIP — ~20-22% weight loss
— Retatrutide — GLP-1 + GIP + Glucagon — 28.7% weight loss in Phase 3

Source: ClinicalTrials.gov — Search LY3437943 | Eli Lilly Pipeline | PharmExec December 2025

Retatrutide is one of the most compelling metabolic research compounds ever studied. The Phase 3 TRIUMPH-4 data — 28.7% weight loss, 86% liver fat reduction, 72% prediabetes reversal, cardiovascular improvements — represents a genuine milestone in metabolic medicine research.

But the long-term picture is still being written. Seven more Phase 3 readouts are coming in 2026. FDA filing is expected Q4 2026. The research community is watching closely — and so are we.

At Better Bio Synthesis, our commitment is transparent truth about peptides. That means sharing what the data shows — and being honest about what it doesn’t show yet. We hope this breakdown helps researchers and curious minds make better informed decisions.

1. Jastreboff AM, et al. Triple-Hormone-Receptor Agonist Retatrutide for Obesity — A Phase 2 Trial. New England Journal of Medicine. 2023;389:514-526. doi:10.1056/NEJMoa2301972

2. Rosenstock J, et al. Retatrutide, a GIP, GLP-1 and glucagon receptor agonist, for people with type 2 diabetes. New England Journal of Medicine. 2023;389:1079-1091. doi:10.1056/NEJMoa2306607

3. Loomba R, et al. Retatrutide for metabolic dysfunction-associated steatotic liver disease. NEJM Evidence. 2023. doi:10.1056/EVIDoa2200291

4. Eli Lilly and Company. TRIUMPH-4 Phase 3 Topline Results Press Release. December 11, 2025. prnewswire.com

5. Eli Lilly Pipeline — Retatrutide (LY3437943). investor.lilly.com/pipeline

6. ClinicalTrials.gov — Search LY3437943. clinicaltrials.gov/search?term=LY3437943

7. Coskun T, et al. LY3437943, a novel triple glucagon, GIP, and GLP-1 receptor agonist. Cell Metabolism. 2022;34(9):1234-1247. doi:10.1016/j.cmet.2022.08.003

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