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 2026 (Lilly release; AJMC coverage), used different arms than phase 2: 4 mg, 9 mg, and 12 mg weekly versus placebo, in 2,339 participants.
| TRIUMPH-1 arm | Mean weight change, 80 wk | 104-wk extension |
|---|---|---|
| 4 mg weekly | −17.6% | — |
| 9 mg weekly | −23.7% | — |
| 12 mg weekly | −25.0% | −30.3% (−85 lbs), no plateau observed |
| Placebo | −3.9% | — |
At 12 mg, 45.3% of participants lost 30% or more of their body weight at 80 weeks — a threshold historically associated with bariatric surgery. 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.
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: in 2024, roughly 43% of research peptides submitted to Janoshik Analytical missed their label claims (an order-of-magnitude signal, not a precise figure). 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.
About PeptideCensus →