What did the first small and mid-sized Phase 2 retatrutide studies find?
For each test, learn about the people, the time under medical watch, and the questions the result leaves open for you.
What should you know before reading retatrutide research?
Retatrutide remains a study drug for obesity and type 2 diabetes. This page follows the human tests in time order and explains their limits. Doctors knew what was in each shot and watched every person closely.
Material bought beyond a study lacks those safeguards. A result first applies to the people who joined, so the same change isn't promised for you. Check who took part and how long they were watched before trusting an average.
The first human test was small. Next came three Phase 2 tests, the mid-sized stage: one for obesity, one for type 2 diabetes, and one Phase 2 test for liver fat in the first human work. Work with cells asked how the drug touches hormone-receiving proteins. The papers appear in Retatrutide references.
What did the first small retatrutide study find in people?
The opening human test was small and short. It included 72 adults with type 2 diabetes and was run by Eli Lilly [4]. The weekly amount reached 12 mg during the 12 weeks.
Doctors found that the amount in blood dropped by half after about 6 days. That span is called the half-life. It helps explain why much of a shot could remain one week later.
During 12 weeks, the largest-amount group lost 8.96 kilograms beyond the average for people who received a placebo [4]. The authors said they were 90% sure the true average gap fell within their stated span, so its exact size remains uncertain. At 3 mg, 63% had side effects, mostly stomach or bowel trouble.
What did Phase 2—the mid-sized test—show after 48 weeks?
This short, 48-week Phase 2 study was a mid-sized test. It included 338 adults with obesity [1]. Some scored 30 or more on a doctor's weight-for-height chart. Others scored 27 up to 30 and had another weight-linked illness, while weekly amounts of 1, 4, 8, and 12 mg rose in steps that aren't personal directions for you.
After 48 weeks, the average person receiving 12 mg had lost −24.2% of starting weight. The placebo group changed −2.1% [1]. Weight loss grew across all four retatrutide amounts, and reviewers in 2025 called the result a sharp break from older drugs [6].
Constipation, diarrhea, nausea, and vomiting were the main troubles. The pulse rose too, reaching its high point near week 24. At the largest amount, 18% left because of side effects [1].
These retatrutide results came from Phase 2, so they aren't the final word. Phase 3 is the larger stage, with more people watched for longer. Those studies will test whether the weight loss and risks hold up. Less than a year can't settle what happens after years or after the drug stops.
What did Phase 2 find in people with type 2 diabetes?
This Phase 2 study was a short, mid-sized test with 281 adults who had type 2 diabetes [2]. Weekly amounts rose slowly and reached 12 mg during the 36 weeks. Other people received a placebo or a different drug so doctors could compare the groups.
For people receiving 12 mg, the three-month blood sugar test fell −2.02 points after 24 weeks. The placebo reading changed −0.01% [2]. That average can't show every daily high or low.
With 12 mg after 36 weeks, body weight fell −16.94%. Placebo weight fell −3.00% [2]. Mild or moderate stomach and bowel trouble affected 35% of the group. Doctors recorded no dangerous low blood sugar and no deaths.
What did Phase 2 find about liver fat after 24 weeks?
This small study included only 98 people with overweight or obesity and fatty liver [5]. A special magnetic scan found that liver fat started at 10% or more. None of the people had type 2 diabetes.
Among those receiving 12 mg, liver fat fell −82.4% after 24 weeks. With 12 mg, eighty-six percent ended below 5%, the level doctors call normal. At 48 weeks, the change was still −86.0% with 12 mg [5].
The result looked large, but the group was small and the study ended before a year. You can't treat that as a settled answer for everyone. Fatty liver often comes with obesity and type 2 diabetes, and no drug was approved just for this kind of fatty liver in 2026, so the finding can't name a care plan for you.
What did close-up lab pictures show about retatrutide?
A 2024 lab study took close-up pictures of retatrutide touching proteins from cells [3]. Those proteins normally receive messages from GLP-1 and two other hormones. No people took part, so the work can't show what would happen to you.
The drug sat against each protein in a different way [3]. That detail helped the makers explain how a single drug could carry three copied messages. It can't tell whether your hunger, blood sugar, pulse, or weight would change.
The makers chose a mild glucagon effect on purpose. A strong effect can raise blood sugar, while a milder one may put more stored fuel to work. The page on how retatrutide works explains why that balance may matter.
What did people taking retatrutide say about hunger and meals?
A 2025 study asked how hunger and eating changed during retatrutide use [8]. Another 2025 paper spoke with 40 people after a Phase 2 trial. Among the 36 who received retatrutide, 31 noticed changes within the first 8 weeks [10].
People described less hunger, smaller helpings, different food choices, and more control over eating. These were their own memories, not blood tests or scale readings. Even so, each person had taken part in a known study.
A 2025 review asked how the gut hormone GLP-1 may affect cravings and parts of the brain tied to reward [7]. Those brain areas can respond to GLP-1. That may help explain why some people said thoughts of food grew quiet.
Retatrutide vs tirzepatide: has one study compared them fairly?
No direct comparison had reported results by mid-2026. A large Phase 3 study is comparing retatrutide with tirzepatide. Until those results arrive, no fair answer is possible.
A separate Phase 2 tirzepatide study found about 20% weight loss over 72 weeks at the largest amount. Tirzepatide copies GLP-1 and one other gut hormone. The retatrutide Phase 2 study found about 24% at 48 weeks. Different people joined, so the separate numbers can't name a winner.
Retatrutide copies GLP-1, another gut hormone, and glucagon rather than GLP-1 alone. Work from 2025 says glucagon may raise daily fuel use [9]. Whether that leads to better Phase 3 results for many people isn't known.
What did newer retatrutide work from 2024–2026 add?
A 2026 study tested mice and hamsters, not people. Mice with obesity lost 31% of their body weight, chose food with less energy, and had less liver fat [13]. In hamsters, muscle and other lean tissue hadn't changed after 5 weeks at the amounts tested. That short animal result can't tell you whether an older man's muscle would remain safe.
One 2026 review found that stomach and bowel trouble often makes people stop this kind of weight drug [12]. Another 2026 review tied nausea from GLP-1 medicines to slower stomach emptying and the part of the brain that causes nausea [12]. A third 2026 paper found reports of burning, prickling, or tingling skin [17], but it couldn't show how often this happened or prove that retatrutide caused it for you.
Is retatrutide FDA approved? No. It wasn't approved by the FDA or any similar agency in mid-2026. Large Phase 3 studies had not finished. Approval depends on their results and a later public review.