Retatrutide Doses in Trials: What the 4, 9 and 12 mg Arms Showed

Retatrutide has no approved dose chart because it isn't approved; Lilly plans to file with the FDA in the first quarter of 2027. Its phase 3 trials tested 4, 9 and 12 mg once a week. In the published TRIUMPH-1 trial, average weight loss at 80 weeks was 17.6%, 23.7% and 25.0%, against 3.9% on placebo.

Those numbers are trial results, not a prescription. Nobody outside a Lilly study is taking retatrutide legally, and the trials themselves were run under close supervision with a fixed step-up schedule. What the arms do give you is the cleanest picture yet of how this drug behaves across its dose range, including at the bottom of it.

If your real question is whether a dose below 1 mg could work, that is a different page: microdosing retatrutide covers why no trial has ever gone that low. This one is about the doses that were studied.

Is retatrutide approved, and when could it be?

No. In August 2026 Lilly said that no medicine containing retatrutide has been approved for human use by any regulator in the world and that it cannot be sold to consumers ⁸. In its July 2026 TRIUMPH-2 and TRIUMPH-3 announcement, the company said it is finishing the manufacturing and quality-control data package a Biologics License Application needs and plans to submit retatrutide for US approval in the first quarter of 2027 ⁶. It repeated the Q1 2027 plan in September ⁷.

A submission starts an FDA review. It is not an approval, and Lilly has not given a date for one.

Which doses were tested?

Two dose sets exist, and they don't line up exactly.

The phase 2 obesity trial (338 adults, 48 weeks) tested 1, 4, 8 and 12 mg. The 4 and 8 mg groups were each split by starting dose, 2 mg or 4 mg, and the 12 mg group started at 2 mg ¹. That design was a deliberate test of how hard to push the first weeks.

Phase 3 settled on 4, 9 and 12 mg. In TRIUMPH-1, everyone on retatrutide started at 2 mg and moved up one step every four weeks: the 4 mg group took a single step from 2 mg, the 9 mg group went through 2, 4 and 6 mg, and the 12 mg group went through 2, 4, 6 and 9 mg ⁵. TRIUMPH-2, in people with type 2 diabetes, and the 40-week TRANSCEND-T2D-1 diabetes trial used the same three target doses ^3,4.

How much weight did each dose take off?

Every trial shows the same shape: more drug, more weight loss, with the gaps narrowing near the top.

Two things to keep in mind when reading that table.

There are two sets of TRIUMPH-1 numbers, and both are real. Lilly's May headline (19.0%, 25.9% and 28.3%) used the efficacy estimand, which estimates what happens if everyone stays on the drug ⁵. The NEJM paper leads with the treatment-regimen estimand, which counts everyone randomized whether or not they kept taking it, and lands at 17.6%, 23.7% and 25.0% ². Lilly's own release reports both ⁵. The lower set is the more realistic expectation for a group of people.

Diabetes changes the numbers. People with type 2 diabetes lose less weight on every incretin drug, and retatrutide is no exception: 11.9%, 16.8% and 18.8% at 80 weeks in TRIUMPH-2 ³, and 11.5%, 13.9% and 15.3% after 40 weeks in TRANSCEND-T2D-1 ⁴.

Two other trials are worth knowing about even though they don't fill out a dose ladder. TRIUMPH-4, in adults with knee osteoarthritis, tested only the 9 and 12 mg doses and reported weight loss of up to 28.7% at 68 weeks ⁹. TRIUMPH-3, in people with severe obesity and established heart disease, also tested only 9 and 12 mg ⁶.

What does the 4 mg arm tell a low-dose reader?

This is the most useful row in the whole program if you care about the low end.

The 4 mg group got there after one step and four weeks at 2 mg. It still lost 17.6% of body weight at 80 weeks by the stricter count ², and 27.8% of that group lost a quarter of their body weight or more by Lilly's efficacy count ⁵. Tripling the dose to 12 mg added about 7 percentage points. That is a real gain, but it is a smaller gain than the first 4 mg delivered over placebo.

The cost side runs the other way. Discontinuation because of side effects was 4.1% at 4 mg, close to the 4.9% on placebo, and 11.3% at 12 mg ⁵.

So the 4 mg arm says the dose-response curve for retatrutide is steep at the bottom and flatter at the top, which is the same pattern seen with semaglutide and tirzepatide. It does not say that a small dose is a small drug. The 17.6% average on 4 mg is higher than the 14.9% that semaglutide 2.4 mg, the standard Wegovy maintenance dose, produced in its pivotal STEP 1 trial ¹⁰. Comparisons across separate trials are rough, but the point stands: 4 mg of retatrutide is a full-strength effect, reached with less titration.

Side effects by dose

Gastrointestinal effects rose with dose in every trial. In phase 2 they were mostly mild to moderate and were partly softened by starting at 2 mg instead of 4 mg; heart rate rose in a dose-dependent way, peaked around week 24 and then eased ¹.

Two effects stand out from the older GLP-1 drugs. Dysesthesia, an abnormal skin sensation such as tingling or skin sensitivity, ran at 5.1% on 4 mg and about 12% on 9 and 12 mg, against 0.9% on placebo; Lilly says most cases were mild to moderate and resolved during treatment ⁵. In TRIUMPH-2, low blood pressure was reported by 1% at 4 mg, 5% at 9 mg and 6% at 12 mg, against under 1% on placebo ³.

Discontinuation does not always climb neatly. In TRIUMPH-2, 4% stopped for side effects at 4 mg, 12% at 9 mg and 8% at 12 mg ³. Small differences between the two top doses are within the noise of a single trial.

Why "research" retatrutide is not a way to get these doses

The trial numbers describe Lilly's drug, made to Lilly's specification, given at a verified strength. Nothing sold online today is that.

The FDA says retatrutide cannot be used in compounding under federal law, is not a component of any FDA-approved drug and has not been found safe and effective for any condition ¹¹. Lilly adds that products sold as "research-use only" are of unknown quality, and it has sued sellers and referred more than 200 people and businesses to regulators and law enforcement ⁸. A vial labeled 10 mg from an unregulated seller could contain more, less, something else, or contaminants. Any dose you calculate from it inherits that uncertainty, which is why the trial table can't be used as a guide for gray-market product. The broader risks of unregulated GLP-1 products are covered in is compounded GLP-1 safe.

What can you take now?

If the 4 mg result is what caught your eye, the approved drugs already offer low-dose starting points with labels behind them. Tirzepatide (Zepbound) starts at 2.5 mg weekly, and the reasons people try to stay near that end are covered in microdosing Zepbound. Foundayo, the daily GLP-1 pill, starts at 0.8 mg, and its low doses and their evidence are mapped out separately. Staying at a starting dose on purpose is still off-label and unproven, but at least the drug in the syringe or bottle is the drug on the label.

For retatrutide itself, the earliest step is a Lilly submission in early 2027, followed by however long the FDA review takes.