GLP-3RT (Retatrutide) Research Literature

If GLP-1 opened the door to metabolic peptide research, GLP-3RT kicked it off the hinges. Known in clinical literature as retatrutide (LY3437943), GLP-3RT is the first triple-receptor agonist — activating GLP-1, GIP, and glucagon receptors simultaneously. That third receptor is what makes it fundamentally different from everything that came before.

GLP-1 agonists suppress appetite. Dual GIP/GLP-1 agonists like tirzepatide add improved insulin sensitivity. GLP-3RT adds a glucagon receptor component that drives something neither of the others can: increased energy expenditure and hepatic fat burning. The body does not just eat less — it burns more.

In June 2023, Eli Lilly published results in The New England Journal of Medicine from a Phase 2 trial of retatrutide that produced numbers nobody had seen before in metabolic research.

The trial enrolled 338 adults with obesity and tested four dosing levels: 1 mg, 4 mg, 8 mg, and 12 mg once weekly, compared to placebo. Here is exactly what researchers observed:

At 24 weeks, the 12 mg group achieved a mean body weight reduction of 17.5% — equivalent to an average loss of 41.2 pounds (18.7 kg). At 48 weeks, that same group reached 24.2% mean body weight reduction — an average loss of 57.8 pounds (26.2 kg).

For context, that is nearly double what semaglutide (a single GLP-1 agonist) achieved in its landmark STEP trials at 68 weeks. Retatrutide achieved more weight reduction in fewer weeks.

Critically, the researchers noted that participants had not yet reached a weight plateau at the 48-week endpoint. Dr. Ania Jastreboff at Yale School of Medicine stated that "full weight reduction efficacy was not yet attained."

The Phase 2 data showed clear dose-dependent outcomes across all groups:

At 48 weeks, the percentage of participants achieving at least 5% weight reduction was 92% at 4 mg, 100% at 8 mg, and 100% at 12 mg — compared to just 27% on placebo.

For at least 15% weight reduction: 60% at 4 mg, 75% at 8 mg, and 83% at 12 mg achieved this threshold — compared to 2% on placebo.

Waist circumference reductions ranged from 6.5 cm to 19.6 cm across retatrutide groups, versus 2.6 cm on placebo.

A substudy published in Nature Medicine in 2024 examined retatrutide's effects on liver fat specifically. The results were remarkable.

Researchers measured liver fat at 24 weeks and found mean relative reductions of 42.9% at 1 mg, 57.0% at 4 mg, 81.4% at 8 mg, and 82.4% at 12 mg — compared to a 0.3% increase on placebo. At the 12 mg dose, 86% of participants achieved normal liver fat levels (below 5%) at 24 weeks. That level of liver fat reduction is unprecedented in published metabolic research.

Phase 3 trials under the TRIUMPH program began in 2024. In December 2025, TRIUMPH-4 data showed 28.7% mean body weight loss over 68 weeks — exceeding even the Phase 2 results and establishing GLP-3RT as the most effective weight reduction compound documented in any published clinical trial.

The safety profile in Phase 2 was similar to existing GLP-1 receptor agonists. Gastrointestinal side effects (nausea, diarrhea, vomiting) were the most commonly reported and were generally mild to moderate, occurring primarily during dose escalation. Heart rate increased in a dose-dependent manner through 24 weeks and declined thereafter. Serious adverse events ranged from 0% to 6% across retatrutide groups, comparable to 4% in the placebo group.

The progression of metabolic peptide research can be traced through receptor count:

- GLP-1 (single agonist): ~15% weight reduction in landmark trials

- Tirzepatide (dual GLP-1/GIP agonist): ~20-22.5% weight reduction

- Retatrutide/GLP-3RT (triple GLP-1/GIP/glucagon agonist): ~24-28.7% weight reduction

The glucagon receptor component is the differentiator. Where GLP-1 reduces intake, glucagon increases expenditure — attacking metabolic research from both sides simultaneously.