Why did phase 3 switch from 8 mg to 9 mg?

Lilly has not published a detailed reason in the sources reviewed here. The phase 2 trials used 8 mg, and the TRIUMPH program lists 4 mg, 9 mg, and 12 mg as maintenance doses. The 9 mg dose sits where 8 mg did in the dose range, between the low and high arms.

What was the highest retatrutide dose tested?

The highest maintenance dose in every published trial is 12 mg once weekly. In phase 2, the 12 mg arm started at 2 mg. In TRIUMPH-1, participants reached 12 mg after four escalation steps spaced 4 weeks apart.

What was the lowest dose tested?

The type 2 diabetes trial in The Lancet included a 0.5 mg weekly arm. It lowered HbA1c by 0.43 percentage points at 24 weeks and body weight by 3.19% at 36 weeks. The obesity trial's lowest dose was 1 mg.

How long did participants stay on each dose?

The phase 2 obesity trial lasted 48 weeks and the diabetes trial lasted 36 weeks. TRIUMPH-1, -2, and -3 ran 80 weeks, and TRIUMPH-4 ran 68 weeks. Some TRIUMPH-1 participants continued on 12 mg to 104 weeks in an extension.

Can I use these trial doses if I buy retatrutide online?

No. Retatrutide is not FDA approved, and no product sold online is the trial drug. The trial doses apply only to verified pharmaceutical material given under medical supervision. Talk with a clinician about approved options.

What Doses of Retatrutide Were Used in the Trials?

The short answer: Retatrutide trials have tested once-weekly injections from 0.5 mg up to 12 mg. The phase 2 obesity trial used 1 mg, 4 mg, 8 mg, and 12 mg for 48 weeks. The phase 3 TRIUMPH program uses 4 mg, 9 mg, and 12 mg, each reached by stepping up from a 2 mg start every 4 weeks. Retatrutide is not FDA approved, so these are study doses, not dosing guidance.

What doses did the phase 2 obesity trial use?

The main obesity study was published by Jastreboff and colleagues in the New England Journal of Medicine in 2023. It enrolled 338 adults with obesity and ran for 48 weeks. Participants were randomized in a 2:1:1:1:1:2:2 ratio to one of six retatrutide arms or placebo.

The arms were defined by both the maintenance dose and the starting dose:

1 mg weekly
4 mg weekly, starting at 2 mg
4 mg weekly, starting at 4 mg
8 mg weekly, starting at 2 mg
8 mg weekly, starting at 4 mg
12 mg weekly, starting at 2 mg
Placebo

Weight loss rose with dose. At 24 weeks, the least-squares mean change in body weight was -7.2% at 1 mg, -12.9% in the combined 4 mg group, -17.3% in the combined 8 mg group, and -17.5% at 12 mg. Placebo was -1.6%. At 48 weeks the figures were -8.7%, -17.1%, -22.8%, and -24.2%, versus -2.1% for placebo.

At 48 weeks, a loss of 15% or more was reached by 60% of the 4 mg group, 75% of the 8 mg group, and 83% of the 12 mg group. Only 2% of placebo participants reached it. Our guide on how much weight people lose on retatrutide covers these results in more detail.

What doses did the phase 2 type 2 diabetes trial use?

Rosenstock and colleagues published the diabetes trial in The Lancet in 2023. It enrolled 281 adults aged 18 to 75 with type 2 diabetes and an HbA1c between 7.0% and 10.5%. Treatment lasted 36 weeks. It added an active comparator, dulaglutide 1.5 mg.

The retatrutide arms were 0.5 mg, 4 mg (starting at 2 mg), 4 mg with no escalation, 8 mg (starting at 2 mg), 8 mg (starting at 4 mg), and 12 mg (starting at 2 mg).

At 24 weeks, HbA1c fell by 0.43 percentage points at 0.5 mg, 1.39 at 4 mg with escalation, 1.30 at 4 mg without escalation, 1.99 at 8 mg with slow escalation, 1.88 at 8 mg with fast escalation, and 2.02 at 12 mg. Placebo fell 0.01 and dulaglutide fell 1.41. Body weight at 36 weeks fell 3.19% at 0.5 mg and 16.94% at 12 mg, versus 3.00% on placebo and 2.02% on dulaglutide. Mild to moderate gastrointestinal events were reported in 67 of 190 retatrutide participants (35%).

What did the liver fat substudy find at each dose?

A substudy of the obesity trial measured liver fat by MRI in 98 participants with metabolic dysfunction-associated steatotic liver disease. Sanyal and colleagues reported it in Nature Medicine in 2024. The doses were the same 1 mg, 4 mg, 8 mg, and 12 mg.

At 24 weeks, the mean relative change in liver fat was -42.9% at 1 mg, -57.0% at 4 mg, -81.4% at 8 mg, and -82.4% at 12 mg. Placebo rose 0.3%. Normal liver fat, defined as below 5%, was reached by 27% at 1 mg, 52% at 4 mg, 79% at 8 mg, and 86% at 12 mg. No placebo participant reached it. The 8 mg and 12 mg results were close.

What doses does the phase 3 TRIUMPH program use?

Lilly moved to phase 3 with a different set of maintenance doses: 4 mg, 9 mg, and 12 mg. The 8 mg dose from phase 2 was replaced by 9 mg. The TRIUMPH design paper, published online in October 2025, describes four registrational trials with more than 5,800 participants combined. The ClinicalTrials.gov entry for TRIUMPH-1 lists the arms only as "Retatrutide Dose 1," "Dose 2," and "Dose 3" plus placebo. The milligram amounts come from Lilly's results announcements.

The registry numbers, per Lilly Medical, are NCT05929066 (TRIUMPH-1), NCT05929079 (TRIUMPH-2), NCT05882045 (TRIUMPH-3), and NCT05931367 (TRIUMPH-4). Here is what each tested:

TRIUMPH-1 (obesity without diabetes, 2,339 participants, 80 weeks): 4 mg, 9 mg, 12 mg, or placebo. Lilly's May 21, 2026 release reported average weight loss of 19.0% (47.2 lb), 25.9% (64.4 lb), and 28.3% (70.3 lb) versus 2.2% (5.5 lb) on placebo. Among 532 participants with a BMI of 35 or higher who stayed on 12 mg to 104 weeks, the average loss was 30.3% (85.0 lb).
TRIUMPH-2 (type 2 diabetes with obesity or overweight, 1,152 participants, 80 weeks): 4 mg, 9 mg, 12 mg, or placebo. Lilly's July 23, 2026 release reported weight loss of 12.7%, 19.1%, and 20.8% versus 4.0% on placebo, with A1C reductions up to 1.6 percentage points versus 0.2 on placebo.
TRIUMPH-3 (BMI of 35 or higher with established cardiovascular disease, 1,949 participants, 80 weeks): 9 mg, 12 mg, or placebo, randomized 1:1:2. Weight loss was 21.6% and 22.6% versus 3.2% on placebo.
TRIUMPH-4 (obesity with knee osteoarthritis, 445 participants, 68 weeks): 9 mg, 12 mg, or placebo. Lilly's December 11, 2025 release reported weight loss of 26.4% (64.2 lb) and 28.7% (71.2 lb) versus 2.1% on placebo. WOMAC pain scores fell 4.5 points (75.8%) at 9 mg and 4.4 points (74.3%) at 12 mg, versus 2.4 points (40.3%) on placebo.

Lilly said it plans to submit a Biologics License Application to FDA in the first quarter of 2027. For the current status of every study, see our retatrutide clinical trials tracker. A head-to-head trial against tirzepatide (TRIUMPH-5, NCT06662383) is still running; mounjaro.md covers that drug.

How were doses escalated, and why?

In phase 2, the 8 mg and 12 mg arms began at 2 mg or 4 mg and stepped up. In TRIUMPH-1, everyone on retatrutide started at 2 mg weekly. The dose rose every 4 weeks until the target was reached. The 4 mg arm needed one step, the 9 mg arm needed three, and the 12 mg arm needed four. TRIUMPH-4 used the same 2 mg start and 4-week steps.

The reason is tolerability. The NEJM authors wrote that gastrointestinal adverse events were dose-related, mostly mild to moderate, and "partially mitigated with a lower starting dose (2 mg vs. 4 mg)." The Lancet trial tested the same idea by giving 4 mg with and without escalation.

Even with slow escalation, side effects rose with dose in phase 3. In TRIUMPH-1, discontinuation due to adverse events was 4.1% at 4 mg, 6.9% at 9 mg, and 11.3% at 12 mg, versus 4.9% on placebo. At 12 mg, nausea occurred in 42.4% of participants versus 14.8% on placebo, and vomiting in 25.3% versus 4.8%. In TRIUMPH-4, 18.2% of the 12 mg group stopped because of adverse events.

Is gray-market "research" retatrutide the same as the trial drug?

No. Every dose in this article was pharmaceutical-grade retatrutide made by Lilly, given under a protocol with lab monitoring. Vials sold online as "research peptides" are not part of any of these trials. Their identity, purity, and actual milligram content are not verified by FDA or by Lilly. A label that says "12 mg" does not mean the vial matches the 12 mg arm of TRIUMPH-1.

The trial dose tables above do not transfer to those products. Our article on gray-market retatrutide explains the risks.

The bottom line

Retatrutide has been studied at 0.5 mg, 1 mg, 4 mg, 8 mg, 9 mg, and 12 mg once weekly. Phase 2 used 1 mg to 12 mg for 48 weeks and showed weight loss of 8.7% to 24.2%. The phase 3 TRIUMPH trials settled on 4 mg, 9 mg, and 12 mg, reached by 4-week steps from a 2 mg start. At 80 weeks in TRIUMPH-1, those doses produced 19.0%, 25.9%, and 28.3% weight loss. Higher doses brought more weight loss and more gastrointestinal side effects. The drug is not FDA approved, and trial doses are not a guide for anyone outside a trial.

Last updated: September 2026. This article is for informational purposes only and does not constitute medical advice. Retatrutide is an investigational drug that is not FDA approved. Trial doses are reported for education and are not a recommendation for use.