--- title: "When Was Retatrutide Created? Timeline 2016 to 2026" description: "Retatrutide entered human trials in 2019, about 7 years ago. A year-by-year timeline from its 2016 design to 2026 Phase 3 data — still investigational." url: https://retatrutide.med/blog/when-was-retatrutide-created date: 2026-07-20 lastUpdated: 2026-07-22 author: "retatrutide.med Editorial" category: "analysis" tags: ["retatrutide history", "timeline", "when was retatrutide created", "drug development", "eli lilly", "ly3437943", "first-in-human", "clinical trials", "investigational", "chronology"] source: retatrutide.med sourceType: "blog post" license: CC-BY-NC-SA-4.0 canonical: https://retatrutide.med/blog/when-was-retatrutide-created --- ## How Long Has Retatrutide Been Around? Retatrutide first entered human testing in 2019, which means it has been in clinical development for roughly seven years as of 2026. It is still an investigational drug — not approved by the FDA or any other regulator — so despite the impressive trial data, no one has ever been able to buy it with a prescription. That gap between "seven years of research" and "still not available" is the whole story of retatrutide's timeline. Below is a direct, year-by-year chronology of how the drug went from a molecule on Eli Lilly's bench to three positive Phase 3 readouts, followed by an honest look at why it has taken this long and what still stands between it and a pharmacy shelf. ## The Timeline at a Glance | Year | Milestone | |---|---| | ~2016–2018 | Molecular design at Eli Lilly; glucagon activity added to the GIP/GLP-1 framework | | 2019 | First-in-human Phase 1 dosing begins | | 2022 | Receptor pharmacology disclosed (Cell Metabolism); Phase 1 results published (The Lancet) | | 2023 | Phase 2 obesity (NEJM) and Phase 2 diabetes (The Lancet); Phase 3 TRIUMPH program announced | | 2024 | Phase 2 liver-fat substudy published (Nature Medicine) | | 2025 | First Phase 3 readout: TRIUMPH-4 (December) | | 2026 | TRIUMPH-1 and TRANSCEND-T2D-1 report; both presented at ADA 2026 | ## Year by Year: How Retatrutide Got Here ### 2016–2018: The Design Phase Retatrutide's development code is LY3437943. The molecule was engineered at Eli Lilly in the mid-to-late 2010s by taking the existing dual GIP/GLP-1 agonist framework — the same lineage that produced tirzepatide — and adding a third action: agonism at the glucagon receptor. That single addition is what makes retatrutide a "triple agonist" and separates it from every approved incretin drug. (For the molecular detail behind that decision, see [what is retatrutide](/knowledge-base/what-is-retatrutide); this post keeps the discovery science to a sentence on purpose.) ### 2019: The First Human Dose The first-in-human Phase 1 study began in 2019. This is the point most people mean when they ask "when was retatrutide invented" or "how long has it been around" — the moment a real person received the drug. Phase 1 trials are small and focus on safety, tolerability, and pharmacokinetics (how the drug moves through the body) rather than weight or blood sugar outcomes. Retatrutide was confirmed as a once-weekly injection with a half-life of roughly six days. ### 2022: The First Public Data Retatrutide surfaced in the scientific literature in 2022. Coskun and colleagues published its receptor pharmacology in *Cell Metabolism*, the first public disclosure of the triple-agonist profile. Later that year, Urva and colleagues published the Phase 1 pharmacokinetic and safety results in *The Lancet*. Until this point, the drug had been largely invisible outside Lilly's pipeline. ### 2023: Phase 2 Puts It on the Map 2023 is the year retatrutide became widely known. Two mid-stage trials reported: - **Phase 2 obesity**, published in the *New England Journal of Medicine* (Jastreboff et al., June 2023). In 338 adults, the highest dose (12 mg) produced a mean weight reduction of 24.2% over 48 weeks — a figure that stood out even against the newest approved drugs. - **Phase 2 type 2 diabetes**, published in *The Lancet* (Rosenstock et al., August 2023). In 281 adults, retatrutide lowered HbA1c by up to 2.02 percentage points and body weight by up to 16.9% at 36 weeks, outperforming the dulaglutide comparator. On the strength of these results, Eli Lilly announced the Phase 3 TRIUMPH program the same year. ### 2024: The Liver Signal In 2024, a substudy of the Phase 2 obesity trial was published in *Nature Medicine* (Sanyal et al.), reporting roughly an 82% relative reduction in liver fat at the highest dose. Because glucagon-receptor agonism directly stimulates the liver to burn fat, this signal hinted at a use beyond weight loss and seeded a dedicated liver-disease program. ### 2025: Phase 3 Begins to Report The first pivotal Phase 3 data arrived on December 11, 2025, when Eli Lilly announced topline results from **TRIUMPH-4** (445 adults with obesity and knee osteoarthritis, 68 weeks). Mean weight loss reached 28.7% at 12 mg versus about 2 to 3% on placebo, with knee-pain scores down about 75%. The trial also brought the drug's class-distinguishing safety signal into focus: dysesthesia — an abnormal skin sensation such as tingling or burning — occurred in 20.9% of the 12 mg group versus 0.7% on placebo. ### 2026: Two More Pivotal Readouts 2026 delivered the data package regulators will lean on: - **TRIUMPH-1** (announced May 21, presented at the American Diabetes Association meeting on June 6) enrolled 2,339 adults with obesity or overweight and no diabetes over 80 weeks. Weight loss reached 28.3% at 12 mg (efficacy estimand), and 65.3% of the 12 mg group finished with a BMI below 30. Nested comorbidity groups showed sleep-apnea and knee-pain benefits too. - **TRANSCEND-T2D-1**, published in full in *The Lancet* on June 6, tested 537 adults with type 2 diabetes on metformin over 40 weeks. HbA1c fell up to 1.94 points and weight up to 15.3% at 12 mg, with a clean dose-response across doses and no severe hypoglycemia in any arm. For the deeper regulatory picture, see [regulatory status](/knowledge-base/regulatory-status). ## Why Has It Taken Seven Years? Seven years from first dose to "still investigational" is not unusual — it is roughly how long modern metabolic drugs take. Each phase is sequential and deliberately slow: Phase 1 establishes safety, Phase 2 finds the dose and first efficacy signals, and Phase 3 enrolls thousands of people and treats them for 40 to 80 weeks before any data emerge. A drug cannot skip ahead. Retatrutide also carries a specific headwind: unlike semaglutide and tirzepatide, it has no prior approval in any indication to build on. That means the FDA will evaluate its entire safety database from scratch, including the novel glucagon component and the dysesthesia signal. What is left: - **Complete the Phase 3 program.** Additional TRIUMPH and TRANSCEND trials are still reporting. - **File a New Drug Application (NDA).** None has been filed as of July 2026; industry estimates point to a Q4 2026 filing built on TRIUMPH-1, TRIUMPH-4, and TRANSCEND-T2D-1. - **FDA review.** A standard 10-to-12-month review (shorter with priority review) points to possible approval in 2027, with a market launch plausibly in the first half of 2028. A fuller account of the milestones lives on the [development history](/knowledge-base/development-history) page. ## Quick Answers **When was retatrutide created?** The molecule was designed at Eli Lilly around 2016 to 2018; it reached its first human dose in 2019. **When did retatrutide come out?** It has not come out. As of July 2026 it remains investigational and is not sold or prescribed anywhere. **How long has retatrutide been around?** About seven years in clinical development, counting from the 2019 first-in-human study. ## A Note Before You Go Everything above describes an experimental medicine that no regulator has approved. All the "week 48" and "week 80" figures are group averages measured inside controlled clinical trials, not outcomes you should expect as an individual, and not endorsements. This article is educational and is not medical advice. If you are weighing options for weight or metabolic health, talk with a licensed clinician about therapies that are actually approved and available today.