Retatrutide study findings: what do the clinical trials show?

What are the real results from retatrutide trials?

In the Phase 2 obesity trial of 338 adults, funded by the developer, the highest arm averaged -24.2% at 48 weeks against -2.1% with placebo, a group average from one 48-week trial (Jastreboff et al., New England Journal of Medicine, 2023). In the Phase 3 TRIUMPH-1 trial of 2,339 adults without diabetes, also funded by the developer, the three arms averaged -17.6% to -25.0% at 80 weeks against -3.9% with placebo, a result that excludes people with diabetes (Jastreboff et al., New England Journal of Medicine, 2026). In TRIUMPH-2, a developer-funded trial, 1,152 adults with type 2 diabetes averaged -11.9% to -18.8% against -5.1%, a result for that population only (Bellido et al., The Lancet, 2026).

These are averages for groups, not forecasts for one person. In the Phase 2 obesity trial of 338 adults, 83% of people in the highest arm had lost at least 15% of body weight at 48 weeks, against 2% on placebo, an early-phase result from a developer-funded trial (Jastreboff et al., NEJM, 2023).

Other trials asked other questions. TRANSCEND-T2D-1 followed 537 adults with type 2 diabetes for 40 weeks and reported HbA1c (a three-month blood-sugar marker) falling 1.69 to 1.94 points across the retatrutide arms against 0.81 with placebo, a result for adults with type 2 diabetes in a developer-funded trial (Bajaj et al., The Lancet, 2026). The retatrutide research guide covers what the compound is.

A before-and-after photo is not a result. It has no comparison group, no measured baseline and no way to separate one compound from everything else that changed in a person's life. Trials close those gaps by design, and that is why this page quotes trials, registries, regulator documents and reviews, each with its source.

Evidence limits

What do the retatrutide studies not show?

Abstracts leave out detail. The journal papers hold tables of side effects by trial arm, and this page cannot quote what it did not read. Where a rate is missing below, the page says so and does not estimate it.

The trials also enrolled screened volunteers. TRIUMPH-1 excluded people with diabetes, a history of pancreatitis, and recent weight-loss drugs (ClinicalTrials.gov NCT05929066), so its averages describe that group. Two other Phase 3 trials, TRIUMPH-3 and TRIUMPH-4, are completed in the registry and have no results posted (ClinicalTrials.gov NCT05882045 and NCT05931367, checked 14 October 2026).

How quickly did weight change in retatrutide trials?

No retatrutide paper opened for this page reports an average weight change at four weeks, so the published time points start later. In the first-in-human study of 45 healthy adults, a body-weight reduction persisted up to day 43 after a single exposure, an early safety-study finding (Coskun et al., Cell Metabolism, 2022). In the 12-week Phase 1b trial of 72 adults with type 2 diabetes, the placebo-adjusted fall reached up to 8.96 kg in the highest group, a result from one small early-phase trial (Urva et al., The Lancet, 2022). In the Phase 2 obesity trial of 338 adults, the highest arm averaged -17.5% at 24 weeks and -24.2% at 48 weeks, a result for that trial population only (Jastreboff et al., NEJM, 2023).

In the Phase 2 obesity trial of 338 adults, weight kept falling between those two time points in every retatrutide arm, from -17.5% to -24.2% in the highest arm and from -7.2% to -8.7% in the lowest, group averages from one developer-funded trial (Jastreboff et al., NEJM, 2023). The curve matters more than any single week.

Some early signals came from interviews, not scales. In an exit-interview study of 40 adults with obesity from the Phase 2 trial, funded by the developer, 31 of 36 retatrutide-treated people said their eating habits had changed within the trial's first 8 weeks, and the authors note that interviews came at one time point at the end of the trial, so recall may be imperfect (Goetz et al., Obesity Pillars, 2025).

No typical first week was found in the sources checked. In the Phase 1b trial of 72 adults with type 2 diabetes, gut disorders were the most frequently reported side effects over its 12 weeks, in a small early-phase trial (Urva et al., The Lancet, 2022), and the side-effect record sits on its own page.

Did every participant in retatrutide trials lose weight?

The reported group averages do not show what each participant lost. In the Phase 2 obesity trial of 338 adults at 48 weeks, 92% of people in the second-lowest arm level had lost at least 5% of body weight and 60% had lost at least 15%, while 27% of people on placebo had lost at least 5%, an early-phase developer-funded trial read from its abstract; the 92% figure implies that some people in that arm lost less than 5%, which does not show weight gain or no weight loss (Jastreboff et al., New England Journal of Medicine, 2023). The abstract gives no responder rows for the lowest arm, and no paper opened for this page explains why one participant lost less than another.

Weight gain is a separate question. Weight increase is not on the ClinicalTrials.gov list of events reported by 5% or more of people in any arm of the 338-adult Phase 2 obesity trial, and that list does not show how many people gained weight (NCT04881760). In the 338-adult Phase 2 obesity trial the placebo group changed too, averaging -2.1% at 48 weeks, a group average from one developer-funded trial (Jastreboff et al., NEJM, 2023).

The exit-interview study gives a human side to the averages. In that study of 40 adults with obesity from the Phase 2 trial, funded by the developer, 30 of 36 retatrutide-treated participants had weight reduction as a goal, 76.7% of those 30 said they reached it, and 3 described frustration with disappointing weight loss, all self-reports that are not measurements (Goetz et al., Obesity Pillars, 2025). This page does not guess at causes for any one person's result.

What do studies show about retatrutide, fat loss and energy?

In a developer-funded substudy of 189 adults with type 2 diabetes, total fat mass measured by DXA scans fell 23.2% in the highest arm and 26.1% in the pooled third-level arms by week 36, against 4.5% with placebo and 2.6% with dulaglutide, in a substudy where only 103 people completed treatment with both scans (Coskun et al., The Lancet Diabetes & Endocrinology, 2025). A DXA scan is an X-ray that separates fat from lean tissue. The word burn implies energy use, and that substudy did not measure it. In an imaging study of 98 adults whose liver fat started at 10% or higher, by authors including developer employees, liver fat fell 82.4% by week 24 in the highest arm, a result from one small study (Sanyal et al., Nature Medicine, 2024).

In the DXA substudy of 189 adults with type 2 diabetes, the body-composition authors report that lean mass made up a similar share of the weight lost as with other obesity treatments, a comparison drawn by developer-funded authors from the 103 people who completed treatment with both scans (Coskun et al., The Lancet Diabetes & Endocrinology, 2025).

Energy use has a mouse result and a human trial with no published numbers yet. In obese mice, glucagon-receptor activity added an increase in energy expenditure to the calorie-intake effect of the other two receptors, a mouse result whose abstract gives no animal count and that does not establish a human result (Coskun et al., Cell Metabolism, 2022). A human study of calorie intake and energy use, NCT06313528, completed on 26 August 2025 and has no results posted (ClinicalTrials.gov, checked 14 October 2026).

Energy as a feeling is a different measure. In the exit-interview study of 40 adults with obesity from the Phase 2 trial, 24 of 36 retatrutide-treated participants reported changes in energy levels that they described as improvements, self-reports that are not a measured energy outcome (Goetz et al., Obesity Pillars, 2025). Fatigue was also a recorded side effect in the Phase 2 obesity trial of 338 adults: 19 of 267 retatrutide participants and 3 of 70 on placebo, which is likewise not a measured energy outcome (ClinicalTrials.gov NCT04881760).

What do studies show about retatrutide and alcohol?

No human study of retatrutide with alcohol was found among the sources opened for this page, and a ClinicalTrials.gov search on 14 October 2026 found no registered retatrutide trial on alcohol use or alcohol interaction among its 34 records. The only alcohol data found for retatrutide come from rats. In a 2026 study in male and female rats, a single treatment with retatrutide, like semaglutide and tirzepatide, weakened the animals' ability to tell alcohol's effects apart, a rat result whose abstract gives no animal count and that does not establish a human result (Windram et al., Psychopharmacology, 2026).

For the wider drug class, one randomised trial in people was found among the sources opened for this page. In 48 adults with alcohol use disorder, semaglutide, not retatrutide, reduced alcohol intake in a laboratory task, drinks per drinking day and craving over 9 weeks, and it did not change average drinks per calendar day or the number of drinking days, in a small 9-week trial whose authors call it initial evidence that justifies larger trials (Hendershot et al., JAMA Psychiatry, 2025).

Hangovers and getting drunk faster are not measured in any study opened for this page. Gastric emptying (the speed at which the stomach empties) was studied for retatrutide in a 2023 paper (Urva et al., Diabetes, Obesity and Metabolism, 2023), and no study opened for this page linked retatrutide to alcohol absorption.

Can retatrutide cause hair loss?

No retatrutide hair-loss rate appears in the sources opened for this page. The posted side-effect table of the Phase 2 obesity trial of 338 adults lists events reported by 5% or more of people in any arm and does not list hair loss (ClinicalTrials.gov NCT04881760), and the posted table of the Phase 2 type 2 diabetes trial of 281 adults, with the same threshold, does not list it either (ClinicalTrials.gov NCT04867785); neither table shows how often hair loss occurred or how it was coded. The Phase 3 papers were read as abstracts, which do not list it. For comparison, the US Zepbound label states that in a pool of two placebo-controlled trials that included 2,519 adults with obesity or overweight treated with tirzepatide, hair loss was reported in 7.1% of female and 0.5% of male patients on tirzepatide against 1.3% and 0% on placebo, and links it to weight reduction, a figure for another medicine in other trials and not a retatrutide rate (DailyMed, 2 September 2026).

The US Wegovy label reports hair loss in 3.3% of patients on semaglutide against 1% on placebo in a pool of three trials of adults with obesity or overweight (2,116 treated with semaglutide and 1,261 on placebo), and also links it to weight reduction, a figure for another medicine in other trials that is not a retatrutide rate (DailyMed, 30 June 2026). A 2026 dermatology review lists alopecia among the skin side effects of the whole drug class, and as a narrative review whose abstract gives no study count it gives no retatrutide rate (Narla et al., Clinics in Dermatology, 2026).

Those are statements about other medicines and about the class. They are not a measured retatrutide rate, and this page does not infer one. The retatrutide side-effect numbers that exist are on the side-effects page.

What causes diarrhoea with retatrutide?

No retatrutide trial opened for this page pinned down one cause of diarrhoea, but these trials show how often it happened. In TRIUMPH-2, a developer-funded trial of 1,152 adults with type 2 diabetes, diarrhoea affected 27%, 34% and 34% of people in the three retatrutide arms against 13% on placebo, a result for that population only (Bellido et al., The Lancet, 2026). In the Phase 2 obesity trial of 338 adults, the registry lists diarrhoea in 37 of 267 retatrutide participants (14%) against 8 of 70 on placebo (11%), counting only events reported by 5% or more of people in any arm of one small developer-funded trial (ClinicalTrials.gov NCT04881760). A 2026 narrative expert review of the drug class, not a trial, lists delayed gastric emptying, altered gut movement and the effects of rapid weight loss as suspected mechanisms for gut side effects, and its abstract gives no study count and does not show them for retatrutide (Singhani et al., Nutrition in Clinical Practice, 2026).

The papers also describe severity. The Phase 2 obesity paper says gut events grew with the trial arm level and were mostly mild to moderate in its 338 developer-funded participants (Jastreboff et al., NEJM, 2023). TRANSCEND-T2D-1, a trial of 537 adults with type 2 diabetes, says they were generally mild to moderate and subsided over time, a developer-funded result for that population (Bajaj et al., The Lancet, 2026).

A suspected mechanism is not a proven cause for retatrutide. Gut side effects also depend on the person, and the trials report group counts only. The side-effects page sets out nausea, vomiting and constipation rates beside diarrhoea.

When were the first retatrutide trials registered and published?

The first retatrutide trial appeared on ClinicalTrials.gov on 15 February 2019 (NCT03841630, a Phase 1 first-in-human safety study). The Phase 2 obesity trial, NCT04881760, was first posted on 11 May 2021, started on 20 May 2021 and was published online in the New England Journal of Medicine on 26 June 2023 (Jastreboff et al., 2023). Its results were first posted on ClinicalTrials.gov on 13 September 2023. The Phase 2 trial in type 2 diabetes, NCT04867785, was published online in The Lancet on the same day (Rosenstock et al., 2023).

The year 2023 causes a common mix-up. It is when Phase 2 results reached print, not when human trials began. Phase 1 started on 13 March 2019 (ClinicalTrials.gov NCT03841630). The first human results paper appeared in 2022 (Coskun et al., Cell Metabolism, 2022).

The Phase 2 paper, read in detail explains which end point was primary and which was secondary. The comparison table below lists the registered trials that matter most, with their first-posted dates.

Which retatrutide Phase 3 trials are registered, and what have they reported?

ClinicalTrials.gov listed 34 retatrutide records on 14 October 2026, and 14 of them are Phase 3. A PubMed search on 14 October 2026 found journal results for three Phase 3 trials: TRANSCEND-T2D-1 in The Lancet on 13 June 2026 (Bajaj et al., 2026), TRIUMPH-1 in the New England Journal of Medicine on 29 September 2026 (Jastreboff et al., 2026) and TRIUMPH-2 in The Lancet on 10 October 2026 (Bellido et al., 2026). TRIUMPH-3 and TRIUMPH-4 are completed with no results posted. Eli Lilly is the lead sponsor of 32 of the 34 records (ClinicalTrials.gov, checked 14 October 2026).

In the 574 participants with knee osteoarthritis, a subgroup of the developer-funded TRIUMPH-1 obesity trial, the WOMAC pain score (a 1 to 10 scale where higher means worse pain) changed by -3.2 to -3.6 in the retatrutide arms against -1.9 with placebo, using the paper's hybrid estimand, a method that handles events such as stopping treatment, in a subgroup result read from the abstract that does not describe other participants (Jastreboff et al., NEJM, 2026).

Several Phase 3 trials are still running. TRIUMPH-5 (NCT06662383) compares retatrutide with tirzepatide in 800 adults and lists its primary completion as estimated for November 2026. TRIUMPH-6 (NCT06859268) tests weight maintenance and lists April 2028. Registry dates are plans, and they change.

Is there a retatrutide clinical trial in Australia, and who can join one?

Yes. Six ClinicalTrials.gov retatrutide records list Australian sites, and one of them, NCT07165028, is recruiting as of 14 October 2026. That Phase 3 trial tests retatrutide and tirzepatide against placebo in adults with metabolic dysfunction-associated steatotic liver disease (MASLD) who are at risk of liver outcomes. Its Australian sites include Fiona Stanley Hospital in Murdoch and a second site in Osborne Park, Western Australia (ClinicalTrials.gov, checked 14 October 2026). The other five Australian-site records are completed or active and not recruiting. Each record sets its own entry rules, and this page does not recruit.

A registry record lists who may take part and where the sites are. NCT07165028 requires liver fat of 8% or more and sets liver-stiffness limits. It excludes people with another liver disease, a body mass index under 25, or type 1 diabetes. It is a liver-outcomes trial, not a weight-loss trial.

The Australian New Zealand Clinical Trials Registry (ANZCTR) is the Australian registry. A search there could not be completed for this page, so a trial listed only on ANZCTR would not appear here. Retatrutide's approval and legal status in Australia covers the TGA position and the registry records in more detail.

Do these findings apply to research-use retatrutide?

No. The human trial results on this page come from trial drug product given to enrolled participants under clinical trial conditions (Jastreboff et al., NEJM, 2026; Bellido et al., The Lancet, 2026), and the mouse and rat findings come from laboratory animals. Research-use reference material is a laboratory compound. Research material is not a medicine, is not a substitute for one, and is not for human or animal use. No trial result here describes it. The TGA reported on 14 September 2026 that one product sold as retatrutide held undeclared semaglutide and no retatrutide, a finding about that one sample (TGA safety alert, 14 September 2026).

What exists for laboratory work is reference material with paperwork. This site's retatrutide reference material listing is freeze-dried laboratory stock. Available reports cover historical samples, and matching current certification is unverified.