Retatrutide is one of the most talked about weight loss drugs in development, with clinical trial results showing some of the largest weight loss numbers seen in this category of medicine. But there is an important fact that gets lost in a lot of online dosing charts: retatrutide is not an approved medicine yet, so there is no official, doctor-prescribed dosing schedule. This guide explains what the clinical trials actually used, what the results were, and what that means for you today.
What Is Retatrutide?
Retatrutide is an experimental drug made by Eli Lilly. It is designed to act on three different hormone receptors at once: GLP-1, GIP, and glucagon. Each of these plays a role in appetite, blood sugar, and how the body burns energy. Because it works on three pathways instead of one or two, it is often called a “triple agonist.” This is different from semaglutide (which acts on one pathway) and tirzepatide (which acts on two).
Is There an Official Retatrutide Dosage?
No. Retatrutide has not been approved by the FDA, so there is no official prescribing dose, no approved starting dose, and no government-approved dosing chart. According to Eli Lilly, the company running the trials, retatrutide is “legally available only to participants in Lilly’s clinical trials.” Source: Eli Lilly investor release
This matters because some dosing charts online are not based on an approved product. They are usually estimates built from the doses used in clinical trials. Anyone who obtains retatrutide from a source other than an approved clinical trial cannot be sure of its purity, dose accuracy, or safety, since it has not gone through the FDA approval process that confirms these things for real medicines.
What Doses Have Been Tested in Clinical Trials?
Even though there is no approved dose, real dosing data does exist from two rounds of Lilly’s own studies. The two trials used somewhat different final dose groups, which is normal as a drug moves through development.
| Trial | Final doses tested | Trial phase |
|---|---|---|
| Phase 2 trial (Jastreboff et al., published in NEJM) | 1 mg, 4 mg, 8 mg, and 12 mg, once weekly | Phase 2 |
| Phase 3 TRIUMPH-1 trial | 4 mg, 9 mg, and 12 mg, once weekly | Phase 3 |
Sources: Eli Lilly Phase 2 release and Eli Lilly Phase 3 TRIUMPH-1 release
In both trials, participants did not simply start at the final dose. Like similar weight loss drugs (semaglutide and tirzepatide), the dose was increased gradually over several weeks. This step by step increase is called dose escalation, and its purpose is to give the body time to adjust and to lower the chance of stomach related side effects. The exact escalation steps used in the trial protocols are not the same as a doctor prescribed schedule you could get today, since again, there is no approved product to prescribe.
Example: think of it like learning to run a long distance. Most people do not run a marathon on day one. They build up gradually. Dose escalation works on a similar idea, just for medication rather than exercise.
Weight Loss Results by Dose
This is where retatrutide has drawn a lot of attention. The numbers below come directly from Lilly’s published trial results.
Phase 2 trial results
- At 24 weeks: the highest dose group lost an average of up to 17.5% of body weight (about 41.2 pounds or 18.7 kilograms)
- At 48 weeks: the highest dose group lost an average of up to 24.2% of body weight (about 57.8 pounds or 26.2 kilograms)
Source: Eli Lilly Phase 2 release
Phase 3 TRIUMPH-1 trial results (80 weeks)
| Dose | Average weight loss (80 weeks) |
|---|---|
| Placebo | 2.2% |
| 4 mg | 19.0% |
| 9 mg | 25.9% |
| 12 mg | 28.3% |
At the 12 mg dose, 45.3% of participants lost 30% or more of their body weight, a result the company compared to outcomes typically seen with bariatric surgery. In a longer extension period for people with a higher starting BMI, the 12 mg group reached an average of 30.3% weight loss. Source: Eli Lilly Phase 3 TRIUMPH-1 release
It is worth noting these are average results across large groups of people. Individual results in any future real world use would likely vary.
Side Effects Seen in Trials
Across both trials, gastrointestinal side effects were the most common issue. Lilly’s own summary describes them as generally mild to moderate and most likely to happen during the dose escalation period, meaning while the dose was still being increased. The overall side effect pattern was described as similar to other drugs in this same hormone-based category, such as semaglutide and tirzepatide. Source: Eli Lilly Phase 2 release
Commonly reported types of side effects in this drug class include:
- Nausea
- Vomiting
- Diarrhea
- Constipation
Because retatrutide is not approved, a full, finalized side effect profile has not been published the way it would be on an approved drug’s label. More complete safety data is expected as Lilly’s additional Phase 3 trials, called TRIUMPH-2 and TRIUMPH-3, are completed and reported. Source: Eli Lilly Phase 3 TRIUMPH-1 release
Why You Should Be Careful About Online Dosing Charts
Because retatrutide is not approved, some of the “dosing charts” and calculators found online are not official medical guidance. They are typically built by taking the doses used in Lilly’s trials and presenting them as if they were a ready-to-use protocol. A few reasons to be cautious:
- The product is not verified. Anything sold outside of Lilly’s approved clinical trials is not guaranteed to be the same compound, at the same strength, tested to the same standard.
- There is no single official schedule. The Phase 2 and Phase 3 trials used different final doses, and Lilly has not published a public, patient-facing prescribing guide, because none exists yet.
- Trial dosing was medically supervised. Every dose increase in these trials happened under close monitoring by research staff, which is very different from self-directed use.
When Might Retatrutide Be Approved?
As of now, retatrutide remains investigational. Lilly has reported successful results from the first Phase 3 trial (TRIUMPH-1) and has said two more Phase 3 trials, TRIUMPH-2 and TRIUMPH-3, were expected to report results later in 2026. Source: Eli Lilly Phase 3 TRIUMPH-1 release A drug typically needs to complete its full Phase 3 program before a company can apply for FDA approval, and the FDA review itself takes additional time after that. No confirmed approval date has been announced, so any specific year mentioned online should be treated as a guess, not a fact.
Questions to Ask Your Provider
If you are interested in retatrutide, or are currently using another weight loss medication and are curious about it, these are useful questions for a licensed provider:
- Am I eligible for any current retatrutide clinical trials?
- Based on my health history, would a triple agonist like this be appropriate for me once available?
- What are the realistic risks of using an unapproved version of this drug from outside a clinical trial?
- What tests should I have done regularly if I am on any GLP-1 or multi-agonist medication?
Frequently Asked Questions
What is the starting dose of retatrutide?
There is no official starting dose because retatrutide is not an approved drug. In Lilly’s own trials, dosing started low and was increased gradually, similar to how other weight loss injections are introduced. Source: Eli Lilly Phase 2 release
What is the maximum dose of retatrutide?
The highest dose tested in both the Phase 2 and Phase 3 trials was 12 mg once weekly. Source: Eli Lilly Phase 3 TRIUMPH-1 release
How do you dose retatrutide?
There is no approved, publicly available dosing protocol yet. What is known comes only from Lilly’s clinical trial designs, where the dose was increased gradually under medical supervision over several weeks.
When did people increase their retatrutide dose in the trials?
Trial protocols increased the dose gradually over multiple weeks rather than jumping straight to the target dose, similar to how semaglutide and tirzepatide are introduced. Exact timing details are part of Lilly’s trial protocols rather than a public prescribing schedule.
Is retatrutide legal to buy?
Retatrutide has not been approved by the FDA and is described by Lilly as legally available only through its clinical trials. Products sold outside of that setting are not verified or approved.
How much weight can you lose on retatrutide?
In Lilly’s Phase 3 TRIUMPH-1 trial, average weight loss at 80 weeks ranged from 19.0% at the 4 mg dose to 28.3% at the 12 mg dose, with some participants reaching over 30% weight loss in a longer extension period.
Important Health Note
Retatrutide is not approved by the FDA and is not currently a legally available medicine outside of clinical trials. The dosing information in this article reflects what has been used in Lilly’s own clinical trials, not an approved prescribing guide, and it may change as research continues. Always speak with a qualified healthcare professional about weight loss options that are currently approved and appropriate for you.
Sources
- Triple-Hormone-Receptor Agonist Retatrutide for Obesity, A Phase 2 Trial, New England Journal of Medicine / PubMed: https://pubmed.ncbi.nlm.nih.gov/37366315/
- Lilly’s Phase 2 retatrutide results published in NEJM, Eli Lilly investor release: https://investor.lilly.com/news-releases/news-release-details/lillys-phase-2-retatrutide-results-published-new-england-journal
- Lilly’s triple agonist, retatrutide, delivered powerful weight loss in pivotal Phase 3 obesity trial (TRIUMPH-1), Eli Lilly investor release: https://investor.lilly.com/news-releases/news-release-details/lillys-triple-agonist-retatrutide-delivered-powerful-weight-loss