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Retatrutide Glossary
Definitions of clinical, regulatory, and pharmacological terms used in retatrutide research. Each entry includes contextual links to the relevant TryTrutide resource.
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Skip to main contentAPI (Active Pharmaceutical Ingredient) The biologically active component of a drug product. In the context of peptides, API refers to the raw peptide compound before formulation. Pharmaceutical-grade API is manufactured under GMP conditions. "Peptide API" sold by research chemical vendors is not pharmaceutical-grade and is not intended for human use.See also: FDA & Regulation BMI (Body Mass Index) A numerical value calculated from a person's weight and height (weight in kg ÷ height in m²). Used as a screening tool in clinical trials to define eligibility criteria. The Phase 2 retatrutide trial enrolled adults with a BMI ≥ 30 kg/m², or ≥ 27 kg/m² with at least one weight-related comorbidity.See also: Clinical Trials COA (Certificate of Analysis) A document from a testing laboratory stating that a compound meets specified purity criteria. A COA does not guarantee sterility, freedom from endotoxins, absence of harmful byproducts, or pharmaceutical-grade manufacturing. Purity does not equal safety for injectable compounds. COAs from unaccredited labs have limited evidentiary value.See also: Safety Center, FDA & Regulation Compounding The preparation of a customized drug product by a licensed pharmacy, typically for an individual patient. Governed by Sections 503A and 503B of the Federal Food, Drug, and Cosmetic Act. Compounding of retatrutide is not legally authorized because retatrutide has no approved NDA.See also: FDA & Regulation FDA (Food and Drug Administration) The U.S. federal agency responsible for regulating drugs, biologics, medical devices, food, and cosmetics. The FDA must approve a New Drug Application (NDA) before a drug can be legally marketed in the United States. Retatrutide has not received FDA approval as of September 2026.See also: FDA & Regulation GIP (Glucose-Dependent Insulinotropic Polypeptide) A hormone secreted by the small intestine in response to food intake. GIP stimulates insulin secretion and may play a role in fat storage and metabolism. Retatrutide activates the GIP receptor as one of its three mechanisms, alongside GLP-1 and glucagon receptors.See also: How It Works GLP-1 (Glucagon-Like Peptide-1) A hormone secreted by intestinal L-cells in response to food intake. GLP-1 stimulates insulin secretion, suppresses glucagon, slows gastric emptying, and signals satiety to the brain. GLP-1 receptor agonists mimic this hormone pharmacologically. Retatrutide activates the GLP-1 receptor as one of its three mechanisms.See also: How It Works, What Is Retatrutide? Glucagon A hormone produced by alpha cells in the pancreas that raises blood glucose by stimulating the liver to release stored glucose. Glucagon receptor agonism, as employed by retatrutide, is hypothesized to increase energy expenditure and promote fat oxidation. The net metabolic effect of glucagon receptor activation in the context of GLP-1/GIP co-agonism is an active area of research.See also: How It Works IND (Investigational New Drug) An application submitted to the FDA by a drug sponsor to begin clinical trials in humans. An IND must be approved before a drug can be tested in human subjects in the United States. Eli Lilly holds an active IND for retatrutide.See also: FDA & Regulation Investigational Drug A drug that has not yet received FDA approval and is being studied in clinical trials. Investigational drugs may only be administered to humans within the context of an authorized clinical trial or under specific FDA-authorized expanded access programs. Retatrutide is an investigational drug.See also: FDA & Regulation, Clinical Trials LY3437943 The internal development code assigned by Eli Lilly to retatrutide. "LY" is Lilly's standard prefix for investigational compounds. The number is an internal identifier. Once a drug receives an International Nonproprietary Name (INN) from the WHO, it is referred to by that name — in this case, retatrutide.See also: What Is Retatrutide? MEN2 (Multiple Endocrine Neoplasia Type 2) A hereditary syndrome caused by mutations in the RET proto-oncogene that predisposes individuals to medullary thyroid carcinoma (MTC), pheochromocytoma, and other endocrine tumors. Personal or family history of MEN2 is an exclusion criterion for retatrutide clinical trials due to the GLP-1 receptor agonist class precaution regarding thyroid C-cell tumors.See also: Safety Center MTC (Medullary Thyroid Carcinoma) A rare cancer arising from thyroid C-cells (parafollicular cells) that produce calcitonin. GLP-1 receptor agonists carry a boxed warning regarding MTC risk based on rodent studies, though a causal relationship in humans has not been established. Personal or family history of MTC is an exclusion criterion for retatrutide trials.See also: Safety Center NDA (New Drug Application) A formal submission to the FDA requesting approval to market a new drug in the United States. An NDA includes clinical trial data, manufacturing information, and proposed labeling. Retatrutide does not yet have an approved NDA.See also: FDA & Regulation Peptide A short chain of amino acids linked by peptide bonds. Peptides are naturally occurring in the body (e.g., GLP-1, insulin) and can also be synthesized for pharmaceutical or research purposes. Retatrutide is a synthetic peptide designed to activate GLP-1, GIP, and glucagon receptors.See also: What Is Retatrutide? Phase 1 Trial The first stage of clinical testing in humans, primarily designed to assess safety, tolerability, pharmacokinetics, and pharmacodynamics. Phase 1 trials typically enroll a small number of healthy volunteers or patients. Retatrutide completed Phase 1 testing before advancing to Phase 2.See also: Clinical Trials, Results & Outcomes Phase 2 Trial The second stage of clinical testing, designed to assess efficacy and further evaluate safety in a larger group of patients with the target condition. The landmark retatrutide Phase 2 trial (Jastreboff et al., NEJM 2023) enrolled 338 adults with obesity and reported up to 24.2% mean weight loss at 48 weeks.See also: Results & Outcomes, Research Library Phase 3 Trial Large-scale clinical trials designed to confirm efficacy, monitor adverse reactions, and compare the drug to existing treatments or placebo. Phase 3 data is required for FDA approval. The TRIUMPH program represents Eli Lilly's Phase 3 retatrutide trials.See also: Clinical Trials, Results & Outcomes Placebo An inactive substance or treatment used as a control in clinical trials. Participants in placebo-controlled trials are randomly assigned to receive either the active drug or placebo, without knowing which they received. Placebo-controlled design helps isolate the drug's true effect from the placebo effect and natural disease progression.See also: Evidence Methodology Randomized Controlled Trial (RCT) A study design in which participants are randomly assigned to treatment or control groups. RCTs are considered the gold standard for evaluating drug efficacy because randomization minimizes selection bias. The Phase 2 retatrutide trial was a randomized, double-blind, placebo-controlled trial.See also: Evidence Methodology Research Use Only (RUO) A designation for laboratory reagents and chemical compounds sold for in-vitro or animal research purposes only — not for human use. RUO products are not manufactured to pharmaceutical standards, are not sterile, and are not intended for injection into humans. Using RUO compounds in humans is illegal and dangerous.See also: FDA & Regulation Retatrutide An investigational once-weekly subcutaneous injection being developed by Eli Lilly and Company (development code: LY3437943). Retatrutide is a triple agonist that activates GLP-1, GIP, and glucagon receptors simultaneously. It is not FDA approved as of September 2026. Phase 2 data reported up to 24.2% mean weight loss at 48 weeks.See also: What Is Retatrutide?, How It Works Semaglutide A GLP-1 receptor agonist approved by the FDA for type 2 diabetes (Ozempic) and chronic weight management (Wegovy). Semaglutide is a single agonist, activating only the GLP-1 receptor. Retatrutide adds GIP and glucagon receptor activation to the GLP-1 mechanism.See also: What Is Retatrutide? Tirzepatide A dual GLP-1/GIP receptor agonist approved by the FDA for type 2 diabetes (Mounjaro) and chronic weight management (Zepbound). Tirzepatide activates two receptors; retatrutide adds glucagon receptor agonism as a third mechanism.See also: Retatrutide vs Tirzepatide TRIUMPH The name of Eli Lilly's Phase 3 clinical trial program for retatrutide. TRIUMPH encompasses multiple trials evaluating retatrutide for obesity, type 2 diabetes, and cardiovascular outcomes. Individual TRIUMPH trials are registered on ClinicalTrials.gov.See also: Clinical Trials Triple Agonist A molecule that activates three distinct receptor types. Retatrutide is a triple agonist of the GLP-1, GIP, and glucagon receptors. This distinguishes it from GLP-1 single agonists (semaglutide) and dual GLP-1/GIP agonists (tirzepatide).See also: How It Works, What Is Retatrutide?