When Was Retatrutide Created? Timeline 2016 to 2026

How Long Has Retatrutide Been Around?

Retatrutide first entered human testing in 2019, so as of 2026 it has been in clinical development for roughly seven years. It is still an investigational drug, not approved by the FDA or any other regulator. 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 plain, year-by-year account of how the drug went from a molecule at Eli Lilly to a full set of positive Phase 3 results, 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 by Year: How Retatrutide Got Here

2016–2018: The Design Phase

Retatrutide’s development code is LY3437943. Eli Lilly engineered the molecule in the mid-to-late 2010s. It took the existing dual GIP/GLP-1 agonist framework, the same line that produced tirzepatide, and added a third action: agonism at the glucagon receptor. That one addition is what makes retatrutide a “triple agonist” and sets it apart from every approved incretin drug. (For the molecular detail behind that choice, see 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 what 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. They focus on safety, tolerability and pharmacokinetics (how the drug moves through the body), not on weight or blood sugar. Retatrutide was confirmed as a once-weekly injection with a half-life of roughly six days.

2022: The First Public Data

Retatrutide appeared in the scientific literature in 2022. Coskun and colleagues published its receptor pharmacology in Cell Metabolism, the first public description of the triple-agonist profile. Later that year, Urva and colleagues published the Phase 1 pharmacokinetic and safety results in The Lancet. Until then, 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. That figure stood out even against the newest approved drugs.
• Phase 2 type 2 diabetes, published in The Lancet (Rosenstock et al., published online June 26, 2023). In 281 adults, retatrutide lowered HbA1c by up to 2.02 percentage points at 24 weeks and body weight by up to 16.9% at 36 weeks, doing better than the dulaglutide comparator.

On the back 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.). It reported roughly an 82% relative reduction in liver fat at the highest dose. Because glucagon-receptor agonism directly prompts the liver to burn fat, this result pointed to a use beyond weight loss and led to 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 2.1% on placebo, and knee-pain (WOMAC) scores fell by up to 75.8%. The trial also brought out the safety signal that sets the drug apart from its class: 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: The Remaining Pivotal Readouts

2026 brought the data package regulators will rely 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. Smaller groups within the trial with related conditions also showed benefits for sleep apnea and knee pain.
• TRANSCEND-T2D-1, published in full in The Lancet on June 6, tested 537 adults with type 2 diabetes managed with diet and exercise alone over 40 weeks. HbA1c fell up to 1.94 points and weight up to 15.3% at 12 mg, with a clear dose-response across doses and no severe hypoglycemia in any arm.
• TRIUMPH-2 and TRIUMPH-3 reported on July 23: 20.8% weight loss at 12 mg in people with type 2 diabetes and 22.6% in people with severe obesity and cardiovascular disease, over 80 weeks. TRIUMPH-1 and TRIUMPH-2 were published on September 29 (NEJM and The Lancet), and the sleep apnea results in NEJM on October 20.
• TRANSCEND-T2D-2, the first head-to-head trial, reported topline results on October 28: in type 2 diabetes, weight fell 20.9% on 12 mg versus 9.4% on semaglutide 2 mg over 80 weeks (not yet peer reviewed).

For the fuller regulatory picture, see Is Retatrutide FDA Approved?.

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. The phases run one after another and are slow by design. Phase 1 establishes safety, Phase 2 finds the dose and the first signs of efficacy, and Phase 3 enrolls thousands of people and treats them for 40 to 80 weeks before any data come out. A drug cannot skip ahead.

Retatrutide also faces a particular hurdle. Unlike semaglutide and tirzepatide, it has no earlier approval for any use to build on. The FDA will review its entire safety database from scratch, including the new glucagon component and the dysesthesia signal.

What is left:

• Complete the Phase 3 program. More TRIUMPH and TRANSCEND trials are still reporting.
• File a marketing application. None has been filed as of October 2026; Eli Lilly plans to file no later than Q1 2027, based on TRIUMPH-1 to -4 and TRANSCEND-T2D-1. The FDA ruled on October 2, 2026 that retatrutide is a drug, so the application must be a New Drug Application (NDA); Lilly is contesting that in court and has not said which pathway it will use (the FDA ruling).
• FDA review. By our estimate, a standard review points to a decision around the first quarter of 2028, and priority review to late 2027. Launch usually follows approval within weeks to a few months.

A fuller account of the milestones is on the 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 October 2026 it is still 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. They are not outcomes you should expect as an individual, and they are not endorsements. This page is educational and is not medical advice. If you are weighing options for weight or metabolic health, talk with a licensed clinician about treatments that are actually approved and available today.