Retatrutide — development code LY3437943, and informally nicknamed "GLP-3" in some circles — is an investigational peptide developed by Eli Lilly and Company. What sets it apart in the crowded field of metabolic research compounds is its design: it is a single molecule engineered to activate three different hormone receptors at once — the GLP-1, GIP and glucagon receptors. This guide summarizes what the peer-reviewed literature and public trial registries report about Retatrutide, and — just as importantly — makes clear what remains unproven and unapproved.
Before going further, one point frames everything below: Retatrutide is not an approved medicine. It is still investigational, meaning it exists in clinical research rather than on pharmacy shelves. Any material supplied to the research community is strictly for laboratory study, not for human use.
The metabolic-peptide field has evolved in generations. First came single GLP-1 receptor agonists. Then came dual agonists that add GIP receptor activity. Retatrutide represents a further step: it targets a third receptor — the glucagon receptor — alongside GLP-1 and GIP. Because glucagon signaling is involved in energy metabolism, the hypothesis behind adding it was that a triple signal might influence the body's energy balance differently than one- or two-receptor approaches. Whether that theoretical advantage holds up across large, long-term human populations is exactly the kind of question that ongoing trials are designed to answer.
Retatrutide is engineered to act as an agonist at the receptors for three distinct metabolic hormones. In plain terms, one peptide is meant to "press three buttons" simultaneously:
The research interest lies in the combination. Rather than optimizing a single pathway, Retatrutide is studied as a way to engage several metabolic pathways together. As with any multi-target compound, that breadth is also why careful, controlled study matters: more targets can mean a more complex overall profile.
The most-cited human data on Retatrutide come from a Phase 2 obesity trial published in the New England Journal of Medicine in 2023 (Jastreboff et al.; registered as NCT04881760 on ClinicalTrials.gov). This randomized, placebo-controlled study evaluated once-weekly subcutaneous Retatrutide across a range of doses versus placebo in adults with obesity, or overweight with weight-related conditions.
Over a 48-week treatment period, the trial reported dose-dependent reductions in body weight. As reported in the trial, the least-squares mean change in body weight reached approximately −24% at the highest dose studied, compared with roughly −2% in the placebo group; intermediate doses fell between those figures. Investigators also noted that participants receiving Retatrutide were still losing weight when treatment ended at week 48. Reported adverse events were most commonly gastrointestinal (such as nausea and related effects) and were described as generally dose-related — consistent with the broader class of incretin-based compounds.
Two caveats belong right next to those numbers. First, these are outcomes measured in clinical-trial participants under medical supervision — they are not a property of any product sold for laboratory research, and nothing here is a promise of any result. Second, Phase 2 is a mid-stage signal, not a final verdict; larger and longer Phase 3 programs are what determine whether such findings hold up and what the full long-term safety picture looks like.
This point is non-negotiable for a responsible sourcing page. As of 2026, Retatrutide has not been approved by the FDA or by any regulatory agency. Eli Lilly describes it as an investigational compound available only through its sponsored clinical trials. It is being evaluated in later-stage (Phase 3) programs across several conditions — including obesity, type 2 diabetes, and other metabolic and related endpoints — but "under study" is not the same as "approved," and long-term human safety and efficacy remain under active investigation.
In practical terms, that means Retatrutide is not a medicine you can be prescribed or a supplement you can take. It is a research-stage molecule. The material supplied to laboratories exists so that scientists can study the compound itself — not so that anyone can self-administer it.
The early-to-mid-stage clinical evidence for Retatrutide is real and published, anchored by a peer-reviewed Phase 2 trial and a registered, ongoing Phase 3 development program. Its mechanism as a GLP-1/GIP/glucagon triple agonist is well characterized in the pharmacology literature.
What is not yet settled is the full long-term picture: durability of effects after treatment stops, the complete safety profile over years rather than months, and how the compound performs across large, diverse populations. Those are precisely the questions Phase 3 trials and post-approval surveillance are built to answer — and until they do, treating mid-stage findings as established, approved outcomes would be a mistake. We won't make that mistake here.
For research applications, identity and purity are what separate a usable reference compound from an unknown. The Retatrutide we supply to the research community is a lyophilized powder with a third-party Certificate of Analysis (COA) available for each lot, strictly for in-vitro laboratory use:
New to handling lyophilized peptides? See our Research Center for storage, reconstitution and COA guidance.
Retatrutide, development code LY3437943 and informally called "GLP-3", is an investigational once-weekly peptide developed by Eli Lilly. It is a triple agonist designed to activate three hormone receptors at once — the GLP-1, GIP and glucagon receptors — and has been studied in clinical trials for obesity and related metabolic conditions.
Retatrutide is engineered to activate the receptors for three metabolic hormones simultaneously: glucagon-like peptide-1 (GLP-1), glucose-dependent insulinotropic polypeptide (GIP), and glucagon. This "triple agonism" distinguishes it from single- or dual-receptor agonists, and researchers have studied whether combining the three signals influences energy balance in metabolic models.
No. Retatrutide is not FDA-approved. It remains an investigational compound that has not been approved by the FDA or any regulatory agency as of 2026, and its long-term human safety is still under study. Any Retatrutide supplied by Universe Peptide is strictly for in-vitro laboratory research and is not for human or animal use.
A Phase 2 obesity trial published in the New England Journal of Medicine in 2023 (Jastreboff et al., NCT04881760) reported dose-dependent reductions in body weight over 48 weeks, with the least-squares mean change reaching roughly −24% at the highest dose studied versus about −2% with placebo. These are clinical-trial findings in study participants and are not a claim about any product sold for research use.