The only published retatrutide dosage is a trial protocol: 1, 4, 8 or 12 mg once weekly for 48 weeks, titrated up over the first 12. No dose has been approved anywhere. A number written into a research protocol isn't a dose, and that gap is the point.
Retatrutide has no approved dose. It's still investigational and now in Phase 3. What exists is a published trial protocol. The Phase 2 trial, Jastreboff et al. in NEJM 2023, used 1, 4, 8 or 12 mg once weekly for 48 weeks. Participants titrated up from 2 mg or 4 mg over about 12 weeks.
“Retatrutide dosage” is one of the most-searched peptide queries there is. Almost everything written about it presents a schedule with more confidence than the evidence supports.
So here's the distinction that matters. There's a trial protocol, published and peer-reviewed, and there's no approved dose. Those aren't the same thing, and the gap between them is where most of the risk lives.
What doses did the trial actually use?
Jastreboff and colleagues randomized 338 adults with obesity to placebo or one of five retatrutide arms, dosed subcutaneously once weekly for 48 weeks. The randomization was 2:1:1:1:1:1. Each active arm was defined by a starting dose and a target dose rather than a single number.
| Arm | Starting dose | Target dose | Weight change at 48 weeks |
|---|---|---|---|
| Placebo | — | — | −2.1% |
| 1 mg | 1 mg | 1 mg | −8.7% |
| 4 mg | 2 mg | 4 mg | −17.1% |
| 8 mg (slow) | 2 mg | 8 mg | −22.8% (combined) |
| 8 mg (fast) | 4 mg | 8 mg | |
| 12 mg | 4 mg | 12 mg | −24.2% |
The published paper grouped the two 8 mg arms together for the headline analysis, which is why you usually see four numbers rather than five. The two-versus-four-milligram starting-dose split existed to answer a specific question: does the route you take to 8 mg change how well you tolerate it?
The finding most dosing charts leave out. The titration schedule wasn't incidental to the result. It was part of the result. Gradual escalation over the first 12 weeks was designed to blunt the dose-dependent gastrointestinal effects that would otherwize have been limiting.
It worked. Slow titration is what kept most participants on the 12 mg arm through all 48 weeks. A chart that lists target doses without the escalation is missing the part that made those doses reachable.
How the escalation was structured
Target dose was reached over roughly the first 12 weeks, with step increases at about four-week intervals. That cadence is consistent across the incretin class. Tirzepatide's SURMOUNT-1 protocol used 2.5 mg increments every four weeks.
Semaglutide's STEP-1 stepped 0.25, 0.5, 1.0, 1.7 then 2.4 mg on the same four-week rhythm. The interval exists because that's roughly how long gastrointestinal tolerance takes to develop at a given dose.
The practical consequence in the trial was that participants spent a meaningful share of the 48 weeks below their target dose. When you read “24.2% at 12 mg,” that is the outcome of a protocol in which 12 mg was reached around week 12, not a description of 48 weeks at 12 mg.
Why there is no approved dose
Retatrutide (development code LY3437943) is in Phase 3. Lilly's TRIUMPH program is running the trials that would support an application. Until those read out and a regulator reviews them, there is no approved indication, no approved dose, no approved titration schedule, and no label. Where the approval process actually stands is worth reading before you treat any number as settled.
This matters for a reason beyond pedantry. Phase 2 doses are dose-finding doses. Their job is to map the response curve, including its top end.
The dose that eventually reaches a label often differs from the highest dose tested in Phase 2. Sometimes the ceiling dose turns out to be poorly tolerated at scale. Sometimes a lower dose captures most of the benefit.
The 12 mg arm produced the largest weight reduction in the trial. That doesn't make 12 mg the answer to a question the trial wasn't asking.
The compounds sold as research retatrutide also aren't the trial material. They're research-use-only reference compounds, a different manufacturing and quality regime from the investigational drug product used in a registrational trial. The difference is substantial, and it isn't primarily about the sequence.
The reconstitution arithmetic
Separate from any dosing question is the plain arithmetic of getting from a lyophilized vial to a concentration. That part isn't clinical judgment, it's division: milligrams in the vial, milliliters of diluent added, and the resulting mg/mL. A 10 mg vial reconstituted with 2 mL of bacteriostatic water gives 5 mg/mL, so 0.1 mL carries 0.5 mg.
Our peptide calculator runs that conversion and shows you the formula, not just the answer. Our reconstitution guide covers why diluent choice and mixing technique matter for a peptide's stability.
GLP3-R (retatrutide)
The triple-agonist reference compound used across the Jastreboff Phase 2 literature. Research use only — supplied with a batch-matched certificate of analysis.
What the dose costs in side effects
Gastrointestinal adverse events in the Phase 2 trial were class-typical: dose-related, mostly mild to moderate, front-loaded into the escalation period.
The trial also documented a dose-dependent heart-rate increase that peaked around week 24 and then declined. That's the cardiovascular signal Phase 3 is positioned to characterize. Our full side-effect page goes through the rates by dose.
What we're watching
Three things. First, what dose or doses TRIUMPH carries into a filing. Phase 3 programs frequently narrow the range tested in Phase 2.
Second, whether the heart-rate signal behaves the same way over longer exposure and in a larger population.
Third, whether the 24.2% headline holds at Phase 3 scale. We'd expect some regression, plausibly into the 18–22% range, which would still lead the class.
Frequently asked questions
What doses of retatrutide were used in the clinical trial?
The Phase 2 trial ran four target doses: 1 mg, 4 mg, 8 mg and 12 mg, injected subcutaneously once weekly for 48 weeks. Participants didn't start there. Every arm titrated up over the first 12 weeks from a 2 mg or 4 mg start, which kept side effects manageable enough for people to stay in.
What is the starting dose of retatrutide in the trials?
2 mg or 4 mg once weekly, depending on the arm. The trial deliberately separated starting dose from target dose. Two of the six arms reached 8 mg, one starting at 2 mg and one at 4 mg, specifically to test whether the escalation route mattered for tolerability. It did.
How long did dose escalation take?
About 12 weeks to reach target dose, with step increases roughly every four weeks. The investigators called slow titration one of the underappreciated findings of the study. It's what kept most participants on the 12 mg arm through the full 48 weeks rather than dropping out over nausea.
Is there an approved retatrutide dose?
No. Retatrutide has no approved dose anywhere in the world because it has no approval anywhere in the world. It is in Phase 3 under Eli Lilly's TRIUMPH program. Any dosing chart presented as official is someone's reconstruction of the trial protocol, at best.
Does a higher retatrutide dose always mean more weight loss?
In the Phase 2 data the dose-response was close to linear up to 12 mg, and the curve hadn't clearly plateaued at the top dose. 12 mg still outperformed 8 mg. It also carried the highest rate of gastrointestinal adverse events and the largest dose-dependent heart-rate increase, which peaked around week 24 before declining.
GLP3-R (retatrutide)
Research-use-only material, sold by the vial with batch documentation. Check the certificate of analysis against the batch you receive.
What to know now
- No approved dose exists. Retatrutide is investigational and now in Phase 3, so there is no label to dose from.
- Phase 2 used 1, 4, 8 or 12 mg once weekly for 48 weeks. Jastreboff and colleagues published it in the NEJM in 2023.
- Escalation took about 12 weeks. Participants started at 2 mg or 4 mg and stepped up toward their assigned target.
- The vial does not know your dose. Reconstitution volume sets the concentration, so every dose rests on arithmetic you do yourself.
- The top dose has a cost. Tolerability is part of the dose question, and the highest arm is not automatically the best one.
References
- Jastreboff, A. M., Kaplan, L. M., Frías, J. P., Wu, Q., Du, Y., Gurbuz, S., Coskun, T., Haupt, A., Milicevic, Z., & Hartman, M. L. (2023). Triple–hormone-receptor agonist retatrutide for obesity — A phase 2 trial. New England Journal of Medicine, 389(6), 514–526. https://doi.org/10.1056/NEJMoa2301972
- ClinicalTrials.gov. A Study of Retatrutide (LY3437943) in Participants Who Have Obesity or Are Overweight (TRIUMPH-1). clinicaltrials.gov retatrutide https://clinicaltrials.gov/search?cond=&term=retatrutide
- Jastreboff, A. M., Aronne, L. J., Ahmad, N. N., et al. (2022). Tirzepatide once weekly for the treatment of obesity. New England Journal of Medicine, 387(3), 205–216. https://doi.org/10.1056/NEJMoa2206038
- Wilding, J. P. H., Batterham, R. L., Calanna, S., et al. (2021). Once-weekly semaglutide in adults with overweight or obesity (STEP-1). New England Journal of Medicine, 384(11), 989–1002. https://doi.org/10.1056/NEJMoa2032183
Dose figures and the titration schedule are from the published Phase 2 protocol; the four-week escalation cadence is compared against the SURMOUNT-1 and STEP-1 protocols cited alongside it.