Retatrutide Clinical Trials: Where We Stand in 2026
Retatrutide (LY3437943) has emerged as one of the most closely watched peptide compounds in metabolic research. Following landmark Phase 2 results published in The New England Journal of Medicine, the compound has entered multiple Phase 3 investigations. This article provides a comprehensive update on the current state of retatrutide clinical research for 2026.
Phase 2 Trial Results: The Foundation
Study Design
The pivotal Phase 2 trial was a 48-week, randomized, double-blind, placebo-controlled study involving 338 adults with obesity (BMI ≥30) or overweight (BMI ≥27) with at least one weight-related comorbidity. Participants were randomized across multiple dose groups ranging from 0.5mg to 12mg administered once weekly via subcutaneous injection. For detailed dosing protocols and reconstitution procedures based on this published data, see our retatrutide dosing guide for researchers.
Primary Outcomes
The results were unprecedented for a Phase 2 trial in this therapeutic area:
- 12mg dose group: Mean body weight reduction of 24.2% at 48 weeks
- 8mg dose group: Mean body weight reduction of approximately 22.8%
- 4mg dose group: Mean body weight reduction of approximately 17.0%
- Placebo: Mean body weight reduction of approximately 2.1%
The 24.2% mean weight reduction at the highest dose exceeded results from Phase 3 trials of both semaglutide (~16.9% in STEP 1) and tirzepatide (~22.5% in SURMOUNT-1), although direct cross-trial comparison requires caution. For a detailed comparison, see our retatrutide vs tirzepatide vs semaglutide breakdown.
Safety Profile
The most commonly reported adverse events were gastrointestinal in nature — nausea, diarrhea, vomiting, and constipation — consistent with the known side-effect profile of GLP-1 receptor agonists. These events were generally mild to moderate, dose-dependent, and most frequent during the dose-escalation period.
MASLD Sub-Study: Hepatic Fat Reduction
A notable sub-analysis examined the effect of retatrutide on hepatic steatosis in participants with baseline metabolic dysfunction-associated steatotic liver disease (MASLD). Data presented at the Canadian Liver Foundation annual meeting showed:
- Significant reductions in liver fat content across all dose groups
- A majority of participants in higher dose groups achieving complete resolution of hepatic steatosis (liver fat <5%)
- Results suggesting the glucagon receptor component may specifically drive hepatic lipid clearance
This hepatic-specific effect is consistent with the known role of glucagon signalling in hepatic lipid metabolism and distinguishes retatrutide from GLP-1-only or GLP-1/GIP compounds in liver-focused metabolic research.
Phase 3 Program: Current Status
Eli Lilly launched an extensive Phase 3 clinical program for retatrutide, known as the TRIUMPH program. Key trials include:
TRIUMPH-1
Evaluating retatrutide for obesity/overweight without type 2 diabetes. This trial enrolled a larger, more diverse population and will provide pivotal efficacy and safety data over 72 weeks.
TRIUMPH-2
Studying retatrutide in adults with obesity/overweight and type 2 diabetes, addressing a key comorbid population.
TRIUMPH-3
A maintenance study evaluating long-term weight maintenance following initial treatment, addressing the critical question of sustained outcomes.
MASLD-Focused Trials
Dedicated trials evaluating retatrutide specifically for metabolic liver disease, leveraging the promising sub-study data from Phase 2.
Trial registration details are available on ClinicalTrials.gov.
What This Means for Researchers
The clinical trial trajectory for retatrutide signals several important developments for the peptide research community:
- Triple-agonism is validated — Phase 2 data confirms that adding glucagon receptor engagement to the GLP-1/GIP backbone produces measurable improvements in research outcomes
- Hepatic applications are expanding — The MASLD data opens new research directions beyond traditional weight-related endpoints
- Phase 3 data expected 2026-2027 — Initial Phase 3 readouts are anticipated in this timeframe, which will provide more robust characterization of the compound
- Research demand is increasing — Access to high-purity retatrutide for preclinical and in vitro studies remains essential for researchers studying multi-receptor peptide biology
For a complete overview of how Canadian researchers can source retatrutide, see our peptide research access guide.
For a foundational understanding of how retatrutide works at the molecular level, read our guide on retatrutide’s mechanism of action.
Canadian researchers looking to work with retatrutide can source third-party tested compound from Great Northern Peptides.
Frequently Asked Questions
What were the Phase 2 results for retatrutide?
The Phase 2 trial showed a mean body weight reduction of 24.2% at the 12mg dose over 48 weeks, published in the New England Journal of Medicine. This was the largest reduction reported in any Phase 2 obesity trial.
When will retatrutide Phase 3 results be available?
The TRIUMPH Phase 3 program is ongoing, with initial readouts anticipated in 2026-2027. Multiple trials are running in parallel, including obesity, type 2 diabetes, and MASLD-specific studies.
Does retatrutide help with fatty liver disease?
Phase 2 sub-study data showed significant hepatic fat reduction, with many participants achieving complete resolution of steatosis. Dedicated Phase 3 MASLD trials are underway to further characterize this effect.
Where can researchers access retatrutide in Canada?
Great Northern Peptides offers third-party tested retatrutide for Canadian researchers, available in 20mg and 40mg vials with domestic Canadian shipping.