Retatrutide dosing information online is a mess of forum lore and vendor blogs. The only dosing data that actually exists comes from Eli Lilly’s clinical trials. That is what this page documents: what the phase 2 and phase 3 trials used, how dose escalation was structured, and the reconstitution math for research contexts. It is a factual summary of published research, not a dosing recommendation; retatrutide is investigational and not approved for use.
In the published phase 2 obesity trial (Jastreboff et al., New England Journal of Medicine, June 2023), participants received once-weekly subcutaneous retatrutide for 48 weeks across four target doses:
| Phase 2 arm (target) | Starting dose | Mean weight change, 24 wk | Mean weight change, 48 wk |
|---|---|---|---|
| 1 mg weekly | 1 mg | −7.2% | −8.7% |
| 4 mg weekly | 2 or 4 mg | −12.9% | −17.1% |
| 8 mg weekly | 2 or 4 mg | −17.3% | −22.8% |
| 12 mg weekly | 2 mg | −17.5% | −24.2% |
| Placebo | — | −1.6% | −2.1% |
In the 12 mg group, 100%, 93%, and 83% of participants lost at least 5%, 10%, and 15% of body weight respectively at 48 weeks.
The first phase 3 results, announced May 21, 2026 (Lilly TRIUMPH-1 release; AJMC coverage), used different arms than phase 2: 4 mg, 9 mg, and 12 mg weekly versus placebo, in 2,339 participants over 80 weeks.
| TRIUMPH-1 arm | Weight change at 80 wk (efficacy estimand) | Weight change at 80 wk (treatment-regimen estimand) |
|---|---|---|
| 4 mg weekly | −19.0% | −17.6% |
| 9 mg weekly | −25.9% | −23.7% |
| 12 mg weekly | −28.3% | −25.0% |
| Placebo | −2.2% | −3.9% |
Lilly reports the results two ways. The efficacy estimand estimates the effect if everyone had stayed on the drug. The treatment-regimen estimand averages everyone who was randomized, including people who stopped, so its numbers are lower. At 12 mg, 45.3% of participants lost 30% or more of their body weight at 80 weeks (efficacy estimand), a threshold historically associated with bariatric surgery. In a pre-specified extension for participants with a baseline BMI of 35 or higher, the 12 mg group reached −30.3% (−85 lbs) at 104 weeks with no plateau observed. All three doses met their primary endpoints.
Neither trial started participants at target dose. Per the phase 2 protocol, arms targeting 4 mg or higher began at 2 mg or 4 mg and escalated every 4 weeks, over up to 12 weeks, until reaching target. The 12 mg arm’s pathway was 2 → 4 → 8 → 12 mg.
| Weeks (12 mg arm, phase 2) | Weekly dose |
|---|---|
| Weeks 1–4 | 2 mg |
| Weeks 5–8 | 4 mg |
| Weeks 9–12 | 8 mg |
| Week 13 onward | 12 mg (maintenance) |
The trial’s most instructive dosing finding: gastrointestinal side effects (the most common adverse events, and dose-related) were partially mitigated by the lower 2 mg starting dose versus 4 mg. Escalation is not an inconvenience layered onto the protocol; it is part of why the protocol worked.
Gastrointestinal effects were the most common side effects in TRIUMPH-1: nausea affected 28.6% to 42.4% of participants depending on dose, against 14.8% on placebo. Diarrhea, constipation and vomiting followed the same pattern, rising with dose. The table shows the rates Lilly reported for the 80-week trial (Lilly TRIUMPH-1 release).
| TRIUMPH-1, 80 weeks | 4 mg | 9 mg | 12 mg | Placebo |
|---|---|---|---|---|
| Nausea | 28.6% | 38.4% | 42.4% | 14.8% |
| Diarrhea | 25.2% | 34.1% | 32.0% | 13.5% |
| Constipation | 23.8% | 25.9% | 26.1% | 10.9% |
| Vomiting | 10.6% | 22.8% | 25.3% | 4.8% |
| Dysesthesia (abnormal skin sensation) | 5.1% | 12.3% | 12.5% | 0.9% |
| Urinary tract infection | 7.5% | 8.8% | 8.4% | 5.3% |
| Stopped treatment due to side effects | 4.1% | 6.9% | 11.3% | 4.9% |
Dysesthesia, a tingling, burning or touch-sensitive feeling in the skin, is the side effect that sets retatrutide apart from older drugs in its class. Lilly describes the dysesthesia and urinary tract infection events as generally mild to moderate. In the phase 2 trial, starting at 2 mg instead of 4 mg partly reduced gastrointestinal side effects, which is why escalation matters.
Retatrutide has no FDA label yet, so it carries no official warnings. Approved drugs in the same incretin class do: Lilly’s safety summary for Zepbound (tirzepatide) warns of possible thyroid tumors, including medullary thyroid carcinoma, inflammation of the pancreas, gallbladder problems, and kidney problems from dehydration when vomiting or diarrhea will not stop. Whether these risks apply to retatrutide is not yet known. Signs that need urgent medical care on approved drugs in this class include severe stomach pain that will not go away, sometimes spreading to the back; vomiting or diarrhea you cannot stop; yellowing of the skin or eyes; and swelling of the face or throat.
Research vials ship as lyophilized powder and are reconstituted with bacteriostatic water. Three numbers determine everything:
All of this math assumes the vial contains what its label claims. Published third-party testing shows that assumption regularly fails in this market: failed results turn up regularly in Janoshik’s public results database. A “12 mg” vial that tests at 9 mg changes every downstream number by 25%. Before relying on any label, check whether the batch has a published test result on the vendor’s PeptideCensus profile.
Is there an official recommended dose? No. Retatrutide is not an approved medicine; the only structured dosing information that exists is the trial protocol data summarized above.
What starting dose did the trials use? Phase 2 arms started at 2 mg or 4 mg weekly, and the trial reported fewer gastrointestinal side effects with the 2 mg start.
Why do phase 2 and phase 3 doses differ? Phase 2 tested 1/4/8/12 mg to find the dose-response range; TRIUMPH-1 carried 4/9/12 mg forward. Dose selection between phases is normal drug development.
Does weight loss plateau? In the TRIUMPH-1 104-week extension, the 12 mg group had not plateaued at −30.3%.
How should vials be stored? Lyophilized (unmixed) vials are typically kept refrigerated and away from light; once reconstituted with bacteriostatic water, research protocols keep vials refrigerated and work within a limited window. Stability varies by compound and preparation; treat vendor storage guidance plus the batch’s test date as your reference points.
How does it compare to tirzepatide or semaglutide dosing? Different molecules, different receptor profiles, different trial ranges; see the tirzepatide and semaglutide hubs.
This article summarizes published clinical research for informational purposes. It is not medical advice, and research compounds are not for human use.
PeptideCensus Editorial is the research team behind the independent peptide lab-result index. Every article is built from published third-party data - trial publications, lab reports, and regulatory records - with every number linked to its source. We don't test, we don't sell, and commissions never touch scores or rankings.
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