Quick answer: in the phase 3 TRIUMPH-1 trial, average retatrutide weight loss over 80 weeks was 17.6% on 4 mg, 23.7% on 9 mg and 25.0% on 12 mg, compared with 3.9% on placebo.[1] People with type 2 diabetes lost less, and Lilly’s headline figures (up to 28.3%) are higher because they assume everyone stayed on treatment.[2]
Retatrutide is an investigational once-weekly injection and is not FDA-approved. This page collects the weight results from every published or company-reported trial. For how it works and its status, see the retatrutide profile; for the dose steps, see the retatrutide dosage guide.
Two ways of counting: why the numbers differ
Trials of weight-loss drugs often report results in two ways:
- Treatment-regimen estimand: counts everyone who was randomized, including people who stopped the drug. This is the main figure in the published TRIUMPH-1 and TRIUMPH-2 papers.[1][3]
- Efficacy estimand: estimates what would have happened if everyone had stayed on treatment. Lilly’s press releases lead with this figure, so it is higher.[2]
Neither is wrong, but compare like with like. A 28% figure from a press release and a 21% figure from another drug’s journal paper are not a fair comparison.
TRIUMPH-1: weight loss in adults without diabetes
TRIUMPH-1 enrolled 2,339 adults with obesity, or overweight with a weight-related condition, and no diabetes. Participants started at 2 mg and stepped up every four weeks to their assigned dose.[1][2] The average starting weight was 112.7 kg (248.5 lb).[2]
| Dose | All randomized (published) | If stayed on treatment (Lilly) | Lost 25% or more | Lost 30% or more |
|---|---|---|---|---|
| 4 mg | −17.6% | −19.0% | 27.8% | 15.3% |
| 9 mg | −23.7% | −25.9% | 52.9% | 37.9% |
| 12 mg | −25.0% | −28.3% | 62.5% | 45.3% |
| Placebo | −3.9% | −2.2% | 2.2% | 0.5% |
Sources: published paper[1] and Lilly topline report (efficacy estimand for the last three columns).[2]
Other results Lilly reported for people who stayed on treatment:[2]
- Waist size fell by 24.1 cm (9.5 inches) on 12 mg, versus 3.6 cm on placebo.
- BMI under 30: 65.3% of people on 12 mg ended the trial below the obesity threshold.
- Weight in pounds: an average of 70.3 lb lost on 12 mg and 47.2 lb on 4 mg.
The 104-week extension
A pre-specified extension followed 532 participants who started with a BMI of 35 or more, finished 80 weeks and tolerated their dose. They were continued for 24 more weeks, with a blinded move up to the highest dose they could tolerate (9 or 12 mg). At 104 weeks, those originally assigned to 12 mg had lost 30.3% on average, or 29.9% counting everyone in the extension.[2] This group was selected for doing well, so it is not representative of everyone who starts the drug.
TRIUMPH-2: obesity with type 2 diabetes
TRIUMPH-2 enrolled 1,152 adults with type 2 diabetes and a BMI of 27 or more. Over 80 weeks, counting everyone randomized, weight fell 11.9% on 4 mg, 16.8% on 9 mg and 18.8% on 12 mg, versus 5.1% on placebo.[3] Lilly’s on-treatment figures were 12.7%, 19.1% and 20.8%, and HbA1c fell by up to 1.6 percentage points.[4]
That is less than in TRIUMPH-1, which enrolled people without diabetes.
TRIUMPH-3 and TRIUMPH-4
| Trial | Who | Weeks | 9 mg | 12 mg | Placebo |
|---|---|---|---|---|---|
| TRIUMPH-3 | 1,949 adults with severe obesity and heart disease | 80 | −21.6% | −22.6% | −3.2% |
| TRIUMPH-4 | 445 adults with obesity and knee osteoarthritis | 68 | −26.4% | −28.7% | −2.1% |
Both rows use Lilly’s efficacy estimand and have not yet been published in a journal.[4][5] For TRIUMPH-4, Lilly also gave the stricter treatment-regimen figures: 20.0% on 9 mg and 23.7% on 12 mg, versus 4.6% on placebo.[5]
TRIUMPH-3 was not designed to prove heart protection. Heart events were fewer than expected in both groups, and the difference between retatrutide and placebo was not statistically significant.[4]
TRANSCEND-T2D-1: early type 2 diabetes
In 537 adults with type 2 diabetes managed by diet and exercise alone, weight fell 11.5%, 13.9% and 15.3% over 40 weeks on the three doses, versus 2.6% on placebo. HbA1c fell by 1.69 to 1.94 percentage points, versus 0.81.[6]
How quickly weight comes off
The phase 2 trial in 338 adults gives the clearest picture of the time course:[7]
| Dose | Week 24 | Week 48 |
|---|---|---|
| 4 mg | −12.9% | −17.1% |
| 8 mg | −17.3% | −22.8% |
| 12 mg | −17.5% | −24.2% |
| Placebo | −1.6% | −2.1% |
Weight was still falling at 48 weeks on the higher doses. By week 48, 83% of people on 12 mg had lost at least 15%, versus 2% on placebo.[7]
In a liver substudy of the same trial, liver fat fell by 82.4% on 12 mg after 24 weeks, and the drop tracked closely with weight and belly-fat loss.[8]
Reading the results: three points to keep in mind
- Higher doses add less each step. In TRIUMPH-1, going from 4 mg to 9 mg added about 6 percentage points of weight loss, but going from 9 mg to 12 mg added only about 1.3.[1] Phase 2 showed the same flattening between 8 mg and 12 mg.[7] Higher doses also brought more stomach side effects; see retatrutide side effects.
- The drug was not used alone. The TRIUMPH trials gave retatrutide alongside advice on healthy eating and physical activity, and the placebo groups received the same support.[5]
- Averages hide a wide range. Even on 12 mg, just over a third of people who stayed on treatment lost less than 25% of their weight.[2]
How it compares and what is still unknown
Retatrutide’s numbers are larger than those in the main trials of tirzepatide and semaglutide, but the trials differed in length, people and analysis. The direct comparison, TRIUMPH-5, is randomizing about 800 adults to retatrutide or tirzepatide, with primary completion estimated for November 2026.[9] See retatrutide vs tirzepatide, retatrutide vs semaglutide, and the separate tirzepatide weight loss results and semaglutide weight loss results.
What happens after stopping is not yet known for retatrutide. TRIUMPH-6, a 643-person trial of weight maintenance, is under way, with primary completion estimated for April 2028.[10] For what trials of other drugs in this class found after stopping, see stopping GLP-1 medications.
Questions to ask a clinician
- What weight loss could I expect from the approved options available to me now?
- Would I qualify for a retatrutide clinical trial?
- How would we judge whether a medicine is working for me, beyond the scale?
- What is the plan if I need to stop?
