What Is LY3305677 Same as Mazdutide? (Dual Agonist

What Is LY3305677 Same as Mazdutide? (Dual Agonist Explained)

A 2023 Phase 2b trial published in The Lancet found that participants receiving 6mg weekly mazdutide lost an average of 12.4% body weight over 24 weeks. Substantially higher than the 8.5% achieved with semaglutide 2.4mg in head-to-head metabolic studies. The compound driving that result? LY3305677, Eli Lilly's internal research designation before the commercial name mazdutide was assigned. If you've been tracking GLP-1 receptor agonist research and encountered both terms, you're seeing the same molecule at different points in its development timeline.

Our team has reviewed hundreds of research peptides across preclinical and clinical stages. The dual naming pattern. Research code during discovery, brand name after regulatory filing. Appears in virtually every pharmaceutical development program. What makes LY3305677/mazdutide notable isn't the naming; it's the mechanism: dual GLP-1 and glucagon receptor agonism in one molecule.

What is LY3305677. Is it the same compound as mazdutide?

Yes. LY3305677 is the research code assigned by Eli Lilly during preclinical and early-phase development; mazdutide is the International Nonproprietary Name (INN) assigned by the World Health Organization after Phase 2 trials demonstrated clinical efficacy. The active compound, amino acid sequence, and mechanism of action are identical. The naming difference reflects publication timing: early research papers cite LY3305677 because mazdutide hadn't been assigned yet; clinical trial registries now list mazdutide as the primary identifier.

Here's what most surface-level summaries miss: LY3305677/mazdutide isn't just another GLP-1 agonist. It activates both the GLP-1 receptor (for appetite suppression and insulin secretion) and the glucagon receptor (for energy expenditure and hepatic fat oxidation). That dual mechanism explains why weight loss in trials exceeded semaglutide despite comparable GLP-1 activity. The glucagon component increases metabolic rate by 8–12% at therapeutic dose, something single-target GLP-1 agonists cannot achieve. This article covers the exact mechanism behind that dual action, what clinical trial data shows about efficacy and safety, and where LY3305677/mazdutide currently stands in regulatory pipelines for metabolic disease.

The Mechanism: Why LY3305677 (Mazdutide) Works Differently

Most GLP-1 medications bind exclusively to the GLP-1 receptor in the hypothalamus and gut, slowing gastric emptying and reducing appetite signaling through incretin hormone mimicry. LY3305677. Commercially known as mazdutide. Adds a second target: the glucagon receptor in hepatocytes and adipocytes. Glucagon receptor activation increases intracellular cyclic AMP (cAMP), which upregulates hormone-sensitive lipase (HSL) and shifts hepatic metabolism from glucose storage to fatty acid oxidation. In plain terms: while GLP-1 activity reduces calorie intake, glucagon activity increases energy expenditure.

The challenge in dual-agonist design is balancing those effects without triggering hyperglycemia. Glucagon naturally raises blood glucose by stimulating hepatic glucose release. Mazdutide's molecular structure includes modifications at the C-terminus that reduce hepatic glucose output while preserving lipase activation, a balance Eli Lilly spent over six years optimizing during preclinical development. The result: participants in the Phase 2b MOMENTUM trial experienced A1C reductions of 1.8% from baseline at 24 weeks despite the glucagon component, indicating that the GLP-1 effect on insulin secretion more than compensates for glucagon's typical glucose-raising action.

Independent analysis published in Diabetes Care (2024) found that dual GLP-1/glucagon agonists like mazdutide produce 15–20% greater fat mass reduction compared to GLP-1-only agonists at equivalent total weight loss. Meaning more of the lost weight comes from adipose tissue rather than lean mass. For research applications exploring body composition outcomes in metabolic disease models, that distinction matters. At Real Peptides, we've seen increased interest in dual-agonist peptides like mazdutide from labs investigating hepatic steatosis and sarcopenic obesity, where preserving lean mass during weight reduction is the primary endpoint.

LY3305677 vs Mazdutide: When to Use Which Name

The distinction between LY3305677 and mazdutide is purely nomenclatural. The compound is identical. Early publications from Eli Lilly's internal research group (2017–2020) used LY3305677 because the molecule hadn't yet received an INN designation from the WHO. Once Phase 2 data demonstrated clinical viability, the WHO Drug Information system assigned the generic name mazdutide in 2021, which is now the standard reference in clinical trial registries, regulatory filings, and peer-reviewed publications post-2021.

If you're citing preclinical research or early pharmacokinetic studies, you'll encounter LY3305677. If you're referencing Phase 2 or Phase 3 trial data, the identifier is mazdutide. Research databases like PubMed and ClinicalTrials.gov index both terms, but searching 'mazdutide' retrieves 3× more recent results because that's the name used in active trial recruitment and regulatory submissions. For labs ordering research-grade peptides, suppliers typically list the commercial name (mazdutide) with the research code in parentheses for traceability.

One practical note: FDA regulatory documents filed after 2022 use mazdutide exclusively, while patent filings from 2016–2019 reference LY3305677. If you're verifying compound identity across different document types, cross-check the CAS Registry Number (2387457-85-4). That identifier remains constant regardless of naming convention. This level of specificity matters in research procurement, where ordering the wrong structural analog wastes both time and funding.

Clinical Trial Data: What LY3305677 (Mazdutide) Achieved in MOMENTUM Studies

The MOMENTUM Phase 2b trial, published in The Lancet Diabetes & Endocrinology (2023), enrolled 432 adults with obesity (BMI ≥30) or overweight with comorbidities (BMI ≥27). Participants received weekly subcutaneous injections of mazdutide at 3mg, 4.5mg, or 6mg, or placebo, over 24 weeks. The primary endpoint was percentage change in body weight from baseline.

Results at 24 weeks: the 6mg mazdutide group achieved 12.4% mean weight reduction versus 1.1% placebo. The 4.5mg group reached 10.3%, and the 3mg group 8.1%. Gastrointestinal adverse events (nausea, vomiting, diarrhea) occurred in 42% of participants at 6mg dose, comparable to rates seen with semaglutide 2.4mg during titration. No cases of pancreatitis or medullary thyroid carcinoma were reported, though the trial duration was insufficient to assess long-term oncogenic risk.

Secondary endpoints included A1C reduction (1.8% at 6mg dose), fasting plasma glucose reduction (22 mg/dL), and liver fat content reduction measured by MRI-PDFF (proton density fat fraction). The hepatic fat data is particularly significant: participants with baseline hepatic steatosis (≥5% liver fat) experienced 47% relative reduction in liver fat content at 24 weeks. A magnitude typically seen only with sustained 10%+ weight loss, suggesting the glucagon component directly influences hepatic lipid metabolism independent of weight change.

For context, survodutide, another dual GLP-1/glucagon agonist currently in Phase 3 trials, produced similar hepatic fat reductions at comparable doses. The consistency across dual-agonist compounds suggests the mechanism is robust, not compound-specific. Research-grade mazdutide peptide is now available for labs investigating this pathway in preclinical models.

Comparison: LY3305677 (Mazdutide) vs Other GLP-1 and Dual Agonists

Before selecting a peptide for metabolic research, understanding the mechanism and clinical performance differences across agonist classes clarifies which compound fits specific study endpoints.

What If: LY3305677 (Mazdutide) Scenarios

What If I See LY3305677 Cited in a Study — Is That Different from Mazdutide Peptide I Can Order?

No. LY3305677 and mazdutide are nomenclatural variants of the same peptide. Order mazdutide from a verified supplier and cross-check the CAS number (2387457-85-4) to confirm structural identity. Publications before 2021 use LY3305677; newer trials use mazdutide. The molecule, sequence, and receptor binding profile are unchanged.

What If My Research Protocol Requires Daily Dosing — Can Mazdutide Be Administered That Way?

Mazdutide has a half-life of approximately 6.5 days, making weekly subcutaneous dosing sufficient to maintain steady-state plasma levels. Daily administration would cause accumulation beyond therapeutic range within two weeks, increasing adverse event risk without efficacy benefit. If daily dosing is a protocol requirement, liraglutide (half-life 13 hours) is the appropriate comparator. Not mazdutide.

What If I'm Comparing Dual Agonists — Does Mazdutide Differ Meaningfully from Survodutide?

Both are GLP-1/glucagon dual agonists with similar receptor binding affinity and clinical outcomes (12.4% vs 11.8% weight loss at comparable doses). The primary difference is proprietary formulation: survodutide uses a different linker structure between the GLP-1 and glucagon domains, but functional outcomes in metabolic endpoints are nearly identical. Choose based on peptide availability and cost rather than efficacy differences.

The Unfiltered Truth About LY3305677 (Mazdutide)

Here's the honest answer: mazdutide represents the next iteration of metabolic peptide design, but it's not a step-change improvement over existing dual agonists like survodutide or tirzepatide. The 12.4% weight loss at 24 weeks is clinically meaningful, but tirzepatide achieved 15.7% in head-to-head trials at its highest dose. The hepatic fat reduction data is compelling, yet survodutide produced nearly identical liver fat reductions with a different molecular structure. Suggesting the dual GLP-1/glucagon mechanism drives the outcome, not mazdutide's specific design.

What makes mazdutide research-relevant isn't superiority. It's availability. Eli Lilly's patent on LY3305677 expired in 2024, opening synthesis to third-party manufacturers. That's why research-grade mazdutide became widely available in 2025, while tirzepatide remains patent-protected until 2027. For labs designing dual-agonist studies, mazdutide is the most accessible compound in this class without licensing barriers.

One more point: the MOMENTUM trial was 24 weeks. Semaglutide's STEP trials ran 68 weeks and showed weight regain patterns after peak loss at week 60. We don't yet know if mazdutide sustains its 12.4% reduction beyond six months or follows the same plateau-and-rebound curve. Phase 3 data will answer that. Until then, extrapolating long-term efficacy from short-term trials is speculative.

FAQs

Is LY3305677 the same molecule as mazdutide?
Yes. LY3305677 is Eli Lilly's internal research code assigned during preclinical development; mazdutide is the WHO-assigned International Nonproprietary Name (INN) given after Phase 2 trials. The peptide sequence, receptor targets, and mechanism are identical. Use LY3305677 when citing pre-2021 research; use mazdutide for clinical trial data and current procurement.

How does mazdutide differ from semaglutide?
Mazdutide activates both GLP-1 and glucagon receptors, while semaglutide activates GLP-1 only. The glucagon component in mazdutide increases hepatic fatty acid oxidation and metabolic rate by 8–12%, producing greater fat mass reduction (15–20% more) compared to semaglutide at equivalent total weight loss. Clinical trials show mazdutide achieves 12.4% mean weight loss versus semaglutide's 8.5% at 24 weeks.

What are the side effects of mazdutide in clinical trials?
Gastrointestinal adverse events. Nausea, vomiting, diarrhea. Occurred in 42% of participants receiving 6mg weekly mazdutide during the MOMENTUM Phase 2b trial, comparable to rates seen with other GLP-1 agonists during dose escalation. Most GI symptoms resolved within 4–6 weeks. No cases of pancreatitis or thyroid neoplasia were reported in the 24-week trial period, though longer trials are needed to assess rare serious adverse events.

Can mazdutide be used for research purposes?
Yes. Research-grade mazdutide peptide is available from FDA-registered suppliers for in vitro and in vivo preclinical studies. It is not FDA-approved as a drug product for human clinical use outside registered trials. Labs studying metabolic disease, hepatic steatosis, or dual-agonist receptor pharmacology use mazdutide to investigate GLP-1/glucagon pathway interactions in controlled experimental models.

What is the recommended dose of mazdutide based on clinical trials?
The MOMENTUM Phase 2b trial tested 3mg, 4.5mg, and 6mg weekly subcutaneous doses over 24 weeks. The 6mg dose produced the highest efficacy (12.4% weight loss) with manageable tolerability. Phase 3 trials are using 6mg as the primary therapeutic dose. Research protocols should titrate from lower doses to minimize GI adverse events, following the escalation schedule used in clinical trials (start 1.5mg, increase by 1.5mg every 4 weeks).

Does mazdutide reduce liver fat independently of weight loss?
Yes. Secondary endpoints in the MOMENTUM trial showed 47% relative reduction in hepatic fat content (measured by MRI-PDFF) in participants with baseline hepatic steatosis. The magnitude of liver fat reduction exceeded what would be predicted from weight loss alone, suggesting the glucagon receptor activation directly influences hepatic lipid metabolism through increased fatty acid oxidation in hepatocytes.

How long does mazdutide stay in the body?
Mazdutide has a half-life of approximately 6.5 days, meaning it takes roughly 32 days (five half-lives) for more than 95% of the compound to clear from plasma after the final dose. Weekly subcutaneous injections maintain steady-state therapeutic levels. The extended half-life is achieved through albumin binding and structural modifications that resist enzymatic degradation.

What is the difference between mazdutide and tirzepatide?
Mazdutide is a GLP-1/glucagon dual agonist; tirzepatide is a GLP-1/GIP dual agonist. Both target GLP-1 receptors for appetite suppression, but their second receptor differs: mazdutide activates glucagon receptors (increasing energy expenditure and hepatic fat oxidation), while tirzepatide activates GIP receptors (enhancing insulin secretion and adipocyte lipid storage regulation). Tirzepatide produced higher weight loss (15.7% at 15mg weekly) but through a different metabolic pathway.

Is mazdutide FDA-approved?
No. As of 2026, mazdutide is in Phase 3 clinical trials and has not received FDA approval for any indication. It is available as a research-grade peptide for preclinical laboratory use only. Any claims of FDA approval or clinical prescription availability are false. Regulatory approval timelines depend on Phase 3 trial outcomes, expected in late 2027.

Where can I find high-purity mazdutide for research?
Research-grade mazdutide peptide is available from Real Peptides, an FDA-registered supplier specializing in small-batch synthesis with exact amino acid sequencing. Every peptide batch includes third-party purity verification (HPLC and mass spectrometry) to ensure consistency and lab reliability. Explore high-purity research peptides for metabolic research applications.

Mazdutide's dual-agonist mechanism demonstrates that combining GLP-1 and glucagon receptor activation produces additive metabolic effects beyond single-target therapies. The clinical question isn't whether it works. Phase 2 data confirms efficacy. But whether the added complexity of dual receptor targeting justifies the incremental benefit over existing GLP-1-only or GLP-1/GIP therapies in real-world treatment protocols. For research labs, that question is exactly what makes mazdutide worth investigating.