Retatrutide Dosage Calculator
Quick answer: Retatrutide is not FDA-approved, so there is no personal dosing recommendation this tool — or anyone — can give you. What it can do is show you exactly what dose was scheduled at any given week inside the published clinical trials, straight from the peer-reviewed data. Pick a trial and a dose arm below to see the studied protocol.
Studied dose at this point in the trial
Phase 2 titration schedule — every studied arm side by side
| Target Dose | Starting Dose | Week 1–4 | Week 5–8 | Week 9–12 | Week 13+ | 48-Wk Result* |
|---|---|---|---|---|---|---|
| 1 mg | 1 mg | 1 mg | 1 mg | 1 mg | 1 mg | Smallest studied effect |
| 4 mg | 2 mg | 2 mg | 4 mg | 4 mg | 4 mg | ~17% |
| 4 mg | 4 mg | 4 mg | 4 mg | 4 mg | 4 mg | ~17% |
| 8 mg | 2 mg | 2 mg | 4 mg | 8 mg | 8 mg | ~22% |
| 8 mg | 4 mg | 4 mg | 8 mg | 8 mg | 8 mg | ~22% |
| 12 mg | 2 mg | 2 mg | 4 mg | 8 mg | 12 mg | ~24% |
*Approximate mean body-weight reduction at 48 weeks, rounded to the nearest whole percent, as reported in Jastreboff et al., N Engl J Med 2023. Individual trial results varied by participant.
What is retatrutide?
Retatrutide, known by its development code LY3437943, is an experimental injectable peptide built to act on three separate metabolic switches at once: the GIP, GLP-1, and glucagon receptors. Most weight-loss injectables on the market today, like semaglutide, work on a single one of these receptors. Tirzepatide works on two. Retatrutide is the first compound to reach late-stage human trials while activating all three, which is part of why its trial results have drawn so much attention from researchers and the media alike.
Is retatrutide FDA-approved?
No. As of today, retatrutide has no approved use anywhere in the world. It exists only inside Eli Lilly’s clinical trial program, known as TRIUMPH, along with a companion diabetes program. Nobody, including a doctor, can legally write you a prescription for it, and there is no manufacturer, pharmacy, or telehealth service that can legitimately sell you the version being tested in these trials. Any product marketed outside a registered trial as “retatrutide for weight loss” sits well outside FDA oversight, and its contents, purity, and dosing accuracy cannot be verified.
How dosing worked in the Phase 2 trial
The foundational human data on retatrutide comes from a Phase 2 trial led by Dr. Ania Jastreboff and colleagues, published in the New England Journal of Medicine in 2023. Investigators split 338 participants across a placebo group and several active-dose groups, each aiming for a different weekly target: 1 mg, 4 mg, 8 mg, or 12 mg. Rather than starting everyone at their full target immediately, most groups began at a lower “starting dose” and stepped up every four weeks, a strategy explained below.
Two of the target-dose groups (4 mg and 8 mg) were further split to compare a gentler 2 mg starting point against a steeper 4 mg starting point. That comparison turned out to matter: participants who began at 2 mg had noticeably fewer stomach-related side effects than those who jumped straight to 4 mg, while ending up at similar weight-loss results after 48 weeks. That single finding shaped how the entire Phase 3 program was later designed.
Why trials increase the dose gradually
- Three receptors, three adjustment periods. Because retatrutide engages GIP, GLP-1, and glucagon receptors simultaneously, the digestive system needs time to adapt to each one rather than all three at once.
- Lower discontinuation. Participants who escalated slowly were far more likely to stay in the trial through its full length than those started at a higher dose.
- Same destination, gentler road. The 48-week weight-loss outcomes for a given target dose were similar regardless of starting dose — the titration schedule changed how the journey felt, not where it ended.
How Phase 3 (TRIUMPH) dosing differs
Eli Lilly’s Phase 3 program, TRIUMPH, is actually a family of separate trials, each studying retatrutide in a different population: general obesity, type 2 diabetes, knee osteoarthritis, obstructive sleep apnea, and more. The first Phase 3 trial to report results, TRIUMPH-4, tested only the two highest doses seen in Phase 2 — 9 mg and 12 mg — in adults with obesity or overweight and knee osteoarthritis, over a longer 68-week period. Announced by Lilly on December 11, 2025, both doses met their primary and secondary goals, with the 12 mg group losing an average of 28.7% of body weight and the 9 mg group losing 26.4%, alongside meaningful improvements in knee pain and physical function.
Six more Phase 3 trials from the TRIUMPH program, plus a separate diabetes program, are expected to report through the rest of this year, including a trial testing a lower 4 mg maintenance dose. Full participant-level results and the detailed dosing protocol for TRIUMPH-4 have not yet appeared in a peer-reviewed journal, which is why this page shows Phase 3 outcomes at a trial level rather than inventing a week-by-week schedule that hasn’t been published.
Why you can’t calculate a personal dose from this data
The numbers on this page describe fixed research protocols applied to specific, medically screened trial populations under close clinical supervision — they were never designed to be scaled to an individual’s weight, goals, or health history outside that setting. A real dosing decision for an investigational drug depends on lab work, medical history, concurrent medications, and in-person monitoring that no calculator, including this one, can replace. If you’re seeing this compound discussed online outside of a registered clinical trial, treat that as a signal to stop and talk to a licensed physician rather than a reason to estimate a dose yourself.
Frequently asked questions
What doses of retatrutide were tested in clinical trials?
The Phase 2 trial tested target doses of 1 mg, 4 mg, 8 mg, and 12 mg weekly, with some groups also comparing a 2 mg versus 4 mg starting dose. The Phase 3 TRIUMPH-4 trial tested only the two highest doses, 9 mg and 12 mg, weekly, over a longer 68-week period.
How long does it take to reach the highest studied dose?
In the Phase 2 trial’s 12 mg arm, participants stepped up every four weeks — 2 mg, then 4 mg, then 8 mg, then 12 mg — reaching the full target dose at week 13, roughly three months after the first dose.
Is retatrutide approved for weight loss?
No. Retatrutide has no FDA approval, EMA approval, or approval from any other regulatory body, for weight loss or any other use. It remains an investigational drug available only inside registered clinical trials.
What’s the difference between Phase 2 and Phase 3 dosing?
Phase 2 tested four target doses (1, 4, 8, and 12 mg) and compared different starting points. Phase 3’s first completed trial, TRIUMPH-4, narrowed the focus to the two highest-performing doses from Phase 2 — 9 mg and 12 mg — and studied them over a longer 68-week period in a larger, more specific patient population.
Why do the trials increase the dose slowly instead of starting at the target?
Because retatrutide activates three separate hormone receptors at once, a gradual increase gives the digestive system time to adjust. Phase 2 data showed that participants who started at a lower dose had meaningfully fewer gastrointestinal side effects than those started at a higher dose, without sacrificing long-term results.
Can I use this tool to figure out my own dose?
No — this tool looks up what dose was scheduled for a given week inside a specific published clinical trial. It isn’t personalized to any individual, and retatrutide isn’t approved for use outside of those trials, so there’s no safe way to convert this data into a personal dosing plan.
References
Jastreboff AM, Kaplan LM, Frías JP, et al. Triple–Hormone-Receptor Agonist Retatrutide for Obesity — A Phase 2 Trial. New England Journal of Medicine, 2023. nejm.org ↗
A Study of Retatrutide (LY3437943) in Participants Who Have Obesity or Overweight and Osteoarthritis of the Knee (TRIUMPH-4). ClinicalTrials.gov identifier NCT05931367. clinicaltrials.gov ↗
Eli Lilly and Company. Lilly’s triple agonist, retatrutide, delivered weight loss of up to an average of 71.2 lbs along with substantial relief from osteoarthritis pain in first successful Phase 3 trial. Investor news release, December 11, 2025. investor.lilly.com ↗
U.S. Food and Drug Administration. Investigational New Drug (IND) Application. Explains why unapproved compounds like retatrutide are legally restricted to registered clinical trials. fda.gov ↗
Eli Lilly and Company, Medical Affairs. Preliminary results with retatrutide from TRIUMPH-4 in participants with obesity or overweight and osteoarthritis. medical.lilly.com ↗
Manzoor is a licensed pharmacist and the founder of DexoCalc, with over 13 years of experience bridging clinical pharmacology and consumer health education. Every figure on this page is sourced directly from peer-reviewed trials or the trial sponsor’s own published data. Read full bio ↗