Retatrutide research spans Phase 1 and Phase 2.

Retatrutide moved from a small study to larger ones

Less hunger may be the first change after a weekly shot. Retatrutide is a lab-made drug. It copies three hormones tied to hunger, insulin, and liver fat. No approved drug copies all three in this way.

Phase 1 was the first small safety test in people. Several Phase 2 studies came next. More Phase 2 work followed. Those studies gave doctors an early look at benefit and harm. One covered obesity. One covered type 2 diabetes. Another covered fatty liver disease. Tests in cells showed how the drug starts three hormone jobs. Larger Phase 3 trials are now underway.

The studies found large changes. In the obesity study, weight fell 24.2% at 48 weeks. In the diabetes study, a long-term sugar reading fell 2.02%. Weight fell 16.94% at 36 weeks. Liver fat fell 82.4% at 24 weeks. Stomach trouble and a faster pulse stood out. Doctors don't know the heart and kidney risks over many years.

For you, those missing years matter.

Retatrutide mimics three hormones

Retatrutide is made in a lab. One added part helps it remain in blood longer. The drug copies three hormones that give orders to cells.

The first hormone, called GLP-1, curbs hunger and slows the stomach. The second, called GIP, helps the body release insulin as sugar climbs. GLP-1 helps with insulin too. The third, called glucagon, helps the body spend stored energy. It may make the liver use more fat. This glucagon effect sets retatrutide apart from drugs that copy two hormones.

In 2024, researchers watched the drug start all three jobs in cells ^[3]. They also measured how much drug each job took. The three jobs began at different amounts. This helps explain the choices behind the drug. It doesn't settle long-term safety.

The how does retatrutide work page names each hormone. It also explains GLP-1 once more.

The cell tests can't tell doctors how you will feel.

Retatrutide was first tested in a small group

The first study included 72 adults with type 2 diabetes. Their long-term sugar readings were between 7.0 and 10.5%. Each received a shot beneath the skin each week. The study used 0.5, 1.5, 3, 3/6, and 3/6/9/12 mg. The slashes show planned increases, not mixed amounts. The study lasted 12 weeks. Retatrutide remained in blood about 6 days ^[4].

The top-dose group lost 8.96 kg more than placebo. Placebo means a shot with no retatrutide. The math gave researchers 90% confidence that the loss wasn't a fluke. They watched the group for 12 weeks. The 3 mg group also had lower daily blood sugar. Side effects arose in 63% of the adults. Most involved the stomach or bowel. The study doctors called the safety results acceptable ^[4].

An added part binds retatrutide to albumin. Albumin is a protein carried in blood. That bond slows the drug's exit from the body.

Your doctor may call the long-term reading a three-month sugar test.

Phase 2 obesity study over 48 weeks

The Phase 2 study enrolled 338 adults. This stage gives an early test of benefit and harm. Each person's weight was high for his or her height. The measure was at least 30. Some measured from 27 to under 30. They also had a health issue tied to weight. Men made up 51.8%. Groups got 1, 4, 8, or 12 mg each week. One group got placebo. Doctors raised some doses during the 48 weeks ^[1].

At 48 weeks, weight fell 8.7%, 17.3%, 22.8%, and 24.2%. Those results match the 1, 4, 8, and 12 mg groups. The placebo group fell 2.1%. Most stomach and bowel trouble was mild or moderate. The pulse climbed more with larger doses. It peaked near week 24. At the top dose, 18% left the study ^[1].

A 2025 review covered 26 studies and 15,491 people without diabetes. It found 22.1% weight loss with retatrutide 12 mg at 48 weeks. Its math put the likely result from 19.3% to 24.9%, with 95% confidence. Tirzepatide 15 mg reached 17.8% after 72 weeks. Semaglutide 2.4 mg reached 13.9% after 68 weeks ^[9]. Phase 2 did not test these drugs together.

Retatrutide vs tirzepatide

No study has tested retatrutide against tirzepatide face to face. Separate Phase 2 papers report 24.2% for retatrutide. A tirzepatide study reported 20.9% with 15 mg. The studies ran for similar lengths of time. Eli Lilly has begun a Phase 3 trial with both drugs. No results are out. Tirzepatide copies two hormone jobs. The GLP-1 hunger job is one of them. Retatrutide also copies glucagon. That hormone affects energy use and liver fat.

You can compare dates and people, but can't name a winner.

Phase 2 study: type 2 diabetes over 36 weeks

This study enrolled 281 adults with type 2 diabetes. It was an early test of benefit and harm. Weekly doses rose from 0.5 to 12 mg. Some people got placebo or another drug. The study ran 36 weeks ^[2].

With 12 mg, the long-term sugar reading fell 2.02% by 24 weeks. Placebo brought a 0.01% fall. By 36 weeks, body weight fell 16.94%. Placebo brought a 3.00% fall. Stomach or bowel trouble affected 35%. Most cases were mild or moderate. No one had a severe sugar drop. No one died. A 2026 review found sugar drops up to 2.16%. Weight fell as much as 26.56% ^[12].

If you use insulin, ask your doctor about that risk.

The fatty liver study followed ninety-eight people

The study followed ninety-eight people with excess weight. All had fatty liver disease. A scan showed at least 10% liver fat. None had type 2 diabetes. Groups got 1, 4, 8, or 12 mg each week. One group got placebo. The study ran 48 weeks ^[5].

At 24 weeks, liver fat fell 42.9%, 57.0%, 81.4%, and 82.4%. Those results match the 1, 4, 8, and 12 mg groups. Placebo brought a 0.3% rise. In the 12 mg group, 86% reached less than 5% liver fat. At 48 weeks, that group was down 86.0%.

A review allowed for the placebo result. It found an 81% drop for retatrutide. That was the largest drop reviewed. Semaglutide showed 41%. Tirzepatide showed 47% ^[7]. Another review covered 25 studies and 2,600 people. Retatrutide had the largest liver-fat drop. Blood tests tied to liver strain also fell ^[8].

A 2025 study in mice found less liver fat and swelling ^[13]. The mice had a fast form of fatty liver disease. Researchers checked the 12 mg result again at week 24. A 2026 Phase 2 review also found signs of help. Those people had diabetes ^[15]. A mouse result can't predict your result.

Your liver scan needs its own medical reading.

Papers from 2024-2025 filled in a few gaps

2024: pictures from cells in a dish. The team saw retatrutide start all three hormone jobs ^[3]. They took a second view of GLP-1, the hunger hormone. A third GLP-1 view confirmed the fit. A fourth GLP-1 test checked the same place.

2025: weight after stopping. One review warned that people regain weight after similar drugs. Retatrutide hasn't been followed long enough to answer that concern ^[10].

2024: newer weight drugs. A Phase 2 review covered retatrutide while it was still in testing. The paper noted its three hormone jobs ^[11].

2026: why weight loss may stop. A review named weight regain after care ends. It was one of three ways care may fail. The authors said early clues may help doctors adjust care ^[14].

2026: all early studies. A Phase 1/2 review found more stomach trouble with some starting amounts. Faster dose increases mattered too ^[12].

A review can guide questions. It can't prove a cause.

Retatrutide research leaves four questions open

Studies of older GLP-1 hunger drugs give some context. Phase 2 work answered short-term questions. It left four gaps.

Heart health. A broad heart study is still running. Phase 2 found a pulse rise at larger doses. That study was too small to judge uneven beats. It also couldn't judge major heart harm.

Kidney health. A kidney trial is running too. Phase 2 left out people with late kidney disease. Doctors still need a study of those people. The current kidney trial asks a different question.

Weight after stopping. People often regain weight after stopping similar drugs. Retatrutide has no published follow-up after stopping.

Muscle over time. A 2025 Phase 2 study found some muscle loss. Phase 3 may show more over a longer time. Another Phase 2 report cannot answer that question. It may also show whether protein and strength work help.

You can check each paper on the Retatrutide references page.

Take these four questions to your doctor.