What have retatrutide studies found by Phase 3?
Phase 2 and other early human tests found less liver fat, falling weight, better blood sugar, and stomach trouble. Longer safety tests aren’t done.
What is the short answer on retatrutide?
No country has approved retatrutide. In 2026, Phase 3 was the large final test round before a company might ask for approval.
Retatrutide acts like three hormones, which are body messages carried in the blood. Together, they may curb hunger, lower blood sugar, and raise the calories used while resting.
The small Phase 1 test first checked how people handled the drug. Later human tests found large drops in weight, stomach trouble, and a pulse that rose with the amount.
Harm after years still isn’t known. The sections below tell you what each fair human test found.
How may retatrutide lead to weight loss?
Retatrutide is made from amino acids, the small parts used to build protein. Its number of parts says nothing by itself about safety.
Three hormones guide retatrutide’s actions; hormones are messages carried in your blood. Those messages affect hunger, blood sugar, stored fat, and calories burned while resting.
One action cuts hunger and makes food remain in the stomach for more time. Another tells the pancreas, an organ behind the stomach, to send out insulin so sugar can move from blood into cells.
The third action may tell the liver to draw on stored fat. It may add to weight loss by raising the calories used while the body rests.
In 2024, scientists tested the drug with cells in dishes and found that it started all three body messages [3]. That work showed what retatrutide could switch on, but not whether the mix would help or harm a person.
The lab tests also found that retatrutide pushed one action much harder than the natural hormone. That difference may help or harm people; the dish test couldn’t say which.
The drug still had to pass Phase 1 and Phase 3 tests in people. A second Phase 3 test can find harm that a short test misses.
Retatrutide also travels with albumin, a common blood protein. As a result, about half remains after 6 days, which fit weekly testing [4].
What did the first small human study find?
In 2022, 72 adults with type 2 diabetes entered the first human study, which lasted 12 weeks [4]. The test asked how their bodies handled the drug.
The adults began with high long-term blood-sugar readings. Each week, a needle put the drug into fat below the skin while doctors checked symptoms and blood tests.
About half the drug remained after 6 days, which fit weekly use. At the largest amount, people given retatrutide lost 8.96 kilograms more than people given placebo, an inactive shot.
The study’s 90% range ran from 6.75 to 11.16 kilograms, so this small test gave a rough answer rather than an exact one. Daily blood sugar also fell at 3 milligrams, a measure of drug weight, while 63% of the people had stomach or bowel trouble.
The findings gave researchers reason to run a larger test. They then began Phase 2, the middle-sized round.
What does the Phase 2 loss of 24.2% mean?
The 2023 Phase 2 weight test followed 338 adults with obesity or another weight-linked health risk. They received weekly shots of 1, 4, 8, or 12 milligrams for 48 weeks [1].
At 48 weeks, average weight fell 24.2% with 12 milligrams and 2.1% with placebo. The other groups lost 8.7% at 1 milligram, 17.3% at 4 milligrams, 22.8% at 8 milligrams, and 24.2% at 12 milligrams.
Stomach and bowel problems grew more common as the amount rose. At 12 milligrams, side effects led 18% to quit.
Higher amounts also brought a larger rise in resting pulse. The pulse climbed most near 24 weeks and then eased somewhat.
In another part, 98 people had fatty liver disease as well as excess weight. With 12 milligrams, liver fat fell 82.4% in 24 weeks, and 86% reached a normal level.
An MRI, a scan made with a large magnet, checked the liver fat without surgery. At 48 weeks, the drop was 86.0% with 12 milligrams [5].
What did Phase 2 find in type 2 diabetes?
In 2023, this Phase 2 study followed 281 adults whose type 2 diabetes wasn’t well controlled [2]. Their long-term blood-sugar readings went as high as 11% before treatment.
Weekly amounts rose in steps to 12 milligrams during 36 weeks. At 24 weeks, the long-term blood-sugar reading fell 2.02% with 12 milligrams, versus 0.01% with placebo.
At 36 weeks, weight fell 16.94%, compared with 3.00% after placebo. About 35% had stomach or bowel trouble, which doctors usually called mild or moderate.
No one died, and people with type 2 diabetes who weren’t taking insulin never needed help for a blood-sugar crash. In 2026, a review ranked retatrutide highest for weight and blood-sugar change among the drugs it compared [13].
What has the first Phase 3 report said so far?
Eli Lilly's TRIUMPH Phase 3 program includes multiple trials covering obesity, type 2 diabetes, cardiovascular outcomes, and chronic kidney disease. The first Phase 3 readout, TRANSCEND-T2D-1, was published in the Lancet in 2026. It enrolled 537 adults with type 2 diabetes inadequately controlled by diet and exercise alone [12].
Over 40 weeks, retatrutide 12 mg reduced HbA1c by 1.94% and body weight by 15.3%, compared with 0.81% HbA1c reduction and 2.6% weight reduction in the placebo group. Adverse events were predominantly mild-to-moderate GI in nature. No severe hypoglycemia was reported in this monotherapy population.
Dedicated cardiovascular and renal outcomes trials remain ongoing. A 2025 evidence review characterized the triple GLP-1/GIP/glucagon agonist class as demonstrating "the highest achievable weight loss with pharmacotherapy" and expected the biochemical and weight-loss outcomes to translate into cardiometabolic benefit [7] — though that translation remains to be confirmed in outcomes trials.
The gap between an early Phase 3 signal and a completed outcomes program also matters when Retatrutide is discussed alongside a clinician-governed Retatrutide prescription category: the mypromise.com practice Promise Peptides represents licensed telehealth oversight, not a route to this investigational compound.
What did the test on heart tissue find?
In 2026, a lab test used small pieces of human upper-heart tissue. Retatrutide made the pieces squeeze harder as the amount rose.
A second lab drug also made the squeeze stronger. When other lab chemicals blocked retatrutide’s three actions in the small pieces of tissue, the harder squeeze stopped; a beta blocker, a common heart drug, did not stop it [8].
This was heart tissue in a dish, not a whole person. The test couldn’t show whether harder squeezing would help or harm someone.
A large heart study is still under way. Until it reports, doctors don’t know whether this finding is tied to a faster pulse, uneven beat, or heart disease.