The investigational triple agonist (GLP-1 + GIP + glucagon) that produced the largest weight reductions ever recorded in a pharmacological trial. Here's what the 2026 Phase 3 TRIUMPH data actually showed, how it differs from tirzepatide and semaglutide, and a side-by-side of vetted vendors for laboratory sourcing.
Retatrutide (development code LY3437943, from Eli Lilly) is an investigational once-weekly peptide that activates three metabolic receptors at once: the receptors for glucagon-like peptide-1 (GLP-1), glucose-dependent insulinotropic polypeptide (GIP), and glucagon. That third arm — glucagon — is what sets it apart from the GLP-1 drugs already on the market and is the focus of intense metabolic research.
As of 2026, retatrutide is not FDA-approved. It is in late-stage Phase 3 development (the TRIUMPH program) and, based on the trial timeline, is projected for a potential regulatory decision around late 2027 to 2028.
Most metabolic peptides engage one or two receptors. Retatrutide engages three, and each adds something different:
For the foundational research, see the retatrutide Phase 2 trial in the New England Journal of Medicine.
Retatrutide's data is why it dominates the metabolic-research conversation. In the Phase 2 trial it produced an average weight reduction of about 24% at 48 weeks — the largest pharmacologically-induced weight loss reported at the time, with the curve still trending downward at trial end. The Phase 3 TRIUMPH program then confirmed and extended those findings:
Lilly is also studying retatrutide for obstructive sleep apnea, chronic low back pain, cardiovascular and renal outcomes, and metabolic liver disease (MASLD).
The simplest way to understand the class is by counting receptors. We break the full head-to-head down in a dedicated guide — Retatrutide vs Tirzepatide vs Semaglutide: 2026 Research Comparison — but in short:
See the full GLP-1 peptide overview and the metabolic & weight research category for context.
Because retatrutide is unapproved and not on the FDA's 503A bulk drug substances list, legitimate compounding does not extend to it. The research-peptide market sells it strictly as a research material. We cover what changed across the category this year in The 2026 FDA Peptide Regulation Update.
Buy directly from vetted research-peptide vendors below. Each product ships from the vendor and is sold strictly for laboratory and research use — not for human consumption. Links are affiliate links, disclosed per FTC guidelines; you pay the same price (and often less with our codes).
| Vendor | From | Form | 3rd-party COA | Shipping | |
|---|---|---|---|---|---|
| Orbitrex PeptidesFinnrick A | $79.99 | ≥99% | ✓ QR-COA every vial | US · same-day | Buy → |
| CD Biolab★ #2 · US lab | $119 | 99%+ | Every batch · on request | US domestic | Buy → |
| GLP-1 Research LabSpecialist | $150 | 30 mg | ✓ HPLC + MS | US · cold-chain | Buy → |
| Midwest PeptideFree shipping | $79.99 | GLP-3 RT | ✓ Every batch | US · free | Buy → |
| Spartan PeptidesCOA-forward | Premium | 6 / 8 mg | ✓ Per-product, signed | US | Buy → |
| Amino Club99%+ guaranteed | $69.99 | GLP-3 | ✓ ISO 17025 | US · free $150+ | Buy → |
| Dynamic PeptidesGMP/ISO | $89.99 | 10 & 30mg | ✓ COA every product | US · 24–48hr | Buy → |
| Pinnacle Peptide LabscGMP US | $149.99 | ≥99% | Independent · COA on request | US · next-day | Buy → |
| Ascension PeptidesMost trusted | $65 | blend / single | ✓ Triple-verified | US · UPS | Buy → |
Prices are starting points and change often. Every outbound buy link is an affiliate link, disclosed per FTC guidelines. Products listed are for laboratory and research purposes only — not for human consumption. Compare all vendors on our peptide company comparison page.
As the name implies, GLP-1 Research Lab focuses on the metabolic category, and they list retatrutide as a 30 mg tri-agonist at $150. Their real differentiator is cold-chain FedEx 2-day shipping — meaningful for peptides where temperature stability matters. Every order includes COA documentation (HPLC + MS). They run an AffiliateWP-style program (our tag ?aff=106 deep-links onto any product). Note: it's a newer, single-category vendor, so verify the current batch COA before purchase. Shop GLP-1 Lab retatrutide → · Read our full review
Ascension is the vendor with the deepest independent reputation on our roster: triple third-party testing (HPLC, mass spec, and LAL endotoxin), ~99.4% purity, a public COA library, and US UPS shipping. They carry the GLP-1 class including sema, tirz and reta. Their /ref/ cookie is set the moment you land, so a researcher can browse the entire catalog (BPC-157, TB-500, blends and more) and stay attributed to us. Shop Ascension → · Read our full review
Midwest lists retatrutide as GLP-3 RT starting at $79.99 — among the most accessible price points — with a Certificate of Analysis on every batch and free shipping on every order. They're a 4.9★ Trustpilot, Kansas-based brand. Our code UNCAGED rides on the link with a 30-day cookie. Shop Midwest retatrutide → · Read our full review
Spartan lists retatrutide as GLP-3 (Reta) in 6 mg and 8 mg vials, each with a signed per-product Certificate of Analysis (HPLC purity, mass-spec identity, chemist signature). Pricing is premium, and they offer metabolic stacks (e.g. their "Skinny Fit Max" with MOTS-c and AOD-9604). Spartan runs the longest window of the group — a 60-day cookie. Shop Spartan retatrutide → · Read our full review
Want the full picture? Compare every vetted vendor on the peptide company comparison page, or see the best peptide companies ranking.
Retatrutide (LY3437943) is an investigational once-weekly peptide that activates three receptors — GLP-1, GIP, and glucagon — at the same time. The glucagon arm adds energy expenditure and lipolysis on top of the appetite and glucose effects of GLP-1/GIP, which researchers believe explains its unusually large effect on body weight in trials.
No. As of 2026 retatrutide is not FDA-approved and is in Phase 3 development (the TRIUMPH program). It is not on the FDA's 503A bulk substances list, so it is sold strictly as a research material. A potential regulatory decision is projected around late 2027–2028.
In Phase 2 it averaged about 24% reduction at 48 weeks. Phase 3 TRIUMPH-1 reported up to 25% at 80 weeks (and ~30% in higher-BMI participants at 104 weeks); TRIUMPH-4 reported 28.7% at 68 weeks. These figures come from clinical trials and describe what the research investigated — not an expected outcome from any research-grade material.
Tirzepatide is a dual agonist (GLP-1 + GIP). Retatrutide adds a third receptor — glucagon — for added thermogenic effect. See our full head-to-head comparison.
Demand batch-specific third-party COAs (HPLC + mass spec), proper cold-chain or stable shipping, U.S. sourcing, and a verifiable reputation. Our vendor comparison checks all of these.
No. We're an independent research and comparison resource. We link to vetted third-party vendors and disclose every affiliate relationship.
Last reviewed June 2026. By the Peptides Uncaged Research Team.
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