Still in study · 1 shot a week · No approval yet
Retatrutide brought 24% average weight loss in Phase 2.
What does that mean for you? Phase 2 is a middle test of results and common problems. Phase 3 uses larger groups to check both again, so you’ll know more later.
Retatrutide is a weekly shot that isn’t approved
Eli Lilly is studying retatrutide as a man-made weekly shot. It’s a peptide: a short chain of about 39 amino acids, which are tiny protein parts. A small fat part is built into the drug. That part helps it stay in your blood for about 6 days [2]. It doesn’t show how long you might feel an effect, so you won’t know that timing from this fact.
The shot starts three actions linked to appetite, stored energy, and sugar in the blood. One copies GLP-1, a body signal that can curb hunger. No approved weight or diabetes drug starts all three actions. Researchers think the mix helped with weight loss in Phase 2. Larger Phase 3 studies are checking that finding and safety [12]. You can’t treat the idea as proved yet.
The hunger action can slow how fast food leaves your stomach. Another action sends insulin into your blood as sugar climbs. The third can make your liver release sugar, which sounds backward. Insulin made by the other two may offset that rise after food. The third may also help your body burn more fuel [4]. You’ll want your doctor to watch both eating and blood sugar.
The main Phase 2 weight study followed 338 adults for 48 weeks. Average weight fell 24.2% in the 12 mg group. People on placebo, the study shot without retatrutide, lost 2.1% [1]. A later review joined the results. Across all groups, sixty-three percent lost at least 15% by 36 weeks [6]. You can’t expect your weight to match either group average.
Retatrutide may burn more fuel than GLP-1 hunger shots
Some approved GLP-1 weight drugs copy the body signal that curbs hunger. Others also help release more insulin after a meal. Retatrutide uses a third action that may increase fuel use [21]. There isn’t a direct human study proving what the extra action adds.
The clearest test was in obese mice, not people. All the mice ate the same number of calories. Mice given retatrutide showed a larger weight drop than mice given a two-action drug. Tests showed greater energy use too [16]. Mice can’t tell us how you would respond.
A lab test showed that 1 piece of the drug could start all 3 actions [4]. The actions weren’t equally strong. Researchers planned that balance so one wouldn’t take over. A lab result still can’t tell which action would matter most in your body.
A 2024 report showed how the three actions work in the lab [4]. That could be one reason for the larger Phase 2 weight change. TRIUMPH-5 is the real check: a Phase 3 study comparing retatrutide with a two-action weight drug in people [20]. You won’t have that direct answer until the study ends.
Phase 2 found weight loss and lower long-term sugar
The New England Journal of Medicine published a Phase 2 weight study in 2023. It followed 338 adults; each had obesity, or had excess weight plus another health problem [1]. Chance assigned every person to placebo or one of four groups: 1 mg, 4 mg, eight milligrams, or 12 mg. Everyone stayed in the study for 48 weeks. Average loss was greater in the higher groups:
- 1 mg group: 8.7% average weight loss
- 4 mg group: 17.1% average weight loss
- 8 mg group: 22.8% average weight loss
- 12 mg group: 24.2% average weight loss
- Placebo: 2.1% average weight loss
The diabetes Phase 2 study followed 281 adults with type 2 diabetes in 2023. At 36 weeks, 82% of the 8 mg group had a result of 6.5% or less. This blood test uses a percent because it checks sugar stuck to red blood cells over recent months. The group average fell by up to 2.02% [3]. That was a direct fall on the test’s percent scale, not a percent of a percent. You can’t assume your result would match.
A review combined studies of 640 people whose groups were chosen by chance [7]. Average blood sugar, cholesterol, blood pressure, and weight all fell. More people taking retatrutide reached every weight mark checked: 5%, 10%, 15%, and 20% or more. Each mark was compared with placebo on its own. You can’t know your mark from the review.
The retatrutide dosage page lists each Phase 2 study amount and explains how quickly the body clears the drug. I’d take that page to your doctor and circle the figures you want explained.
Four larger Phase 3 studies check more than weight
TRIUMPH is Lilly’s name for four large Phase 3 studies of weight-linked health problems [12]. More than 5,800 people are taking part. The studies are checking retatrutide for:
- Obesity and body weight
- Sleep apnea, which causes pauses in breathing
- Knee arthritis and pain
- Heart and kidney health over a longer time
TRIUMPH-1, one Phase 3 study, found about 28% average weight loss at 48 weeks with the highest study amount. As of 2026, no Phase 3 weight-drug study had reported a larger average. TRIUMPH-5 began in November 2024. It’s the first study comparing retatrutide directly with a weight drug that has two similar actions [20].
Retatrutide remains investigational and has no FDA approval for any use. Authorized clinical use takes place in studies such as the TRIUMPH Phase 3 work; research-labelled retatrutide is also sold, but those sales do not provide a prescription route. The research page gives the full FDA approval status.
Studies found changes in the liver and kidneys
A Phase 2 fatty-liver study followed 98 people for 24 weeks in 2024 [5]. Researchers used a scan to measure liver fat. It fell 42.9% at 1 mg, 57.0% at 4 mg, 81.4% at 8 mg, and 82.4% at 12 mg. Placebo brought a +0.3% change. In the 12 mg group, liver fat was normal in eighty-six percent, meaning under 5%. One blood test for liver-cell harm, called K-18, also improved. A test tied to liver scarring improved too. Your liver might not change the same way.
A later review of two Phase 2 studies checked kidney health [9]. With 12 mg, a urine sign of kidney strain fell 37% in people with type 2 diabetes. It also fell 31.5% in people with obesity but no diabetes. A blood estimate of kidney filtering improved in the 8–12 mg groups. That result led to another study in adults with extra weight and long-term kidney disease [13]. One study can’t tell how well your kidneys work.
The retatrutide side effects page covers stomach, bowel, heart, and other problems from the studies. It also explains what doctors watch during stomach and bowel trouble. Bring your own test results to your visit. They give your doctor the part these averages can’t.