A study-by-study look at retatrutide clinical trials: what has been published, what is still running, and what it could mean for people using Mounjaro.
Last updated: this post reflects publicly available information as of its publication date. Scheduled review: six months after publication.
Retatrutide clinical trials are some of the most closely watched studies in obesity research right now. Eli Lilly is developing the molecule, and it belongs to the same broad family as tirzepatide, the active ingredient in Mounjaro. It is still investigational, though, so you can't get it as a treatment. This post walks through the program study by study, so you can see what has been published, what is still running, and what it could mean if you already use Mounjaro.
What Retatrutide Is
Retatrutide is a single molecule that binds to three receptors: GIP, GLP-1, and glucagon. Tirzepatide binds to only two of them, GIP and GLP-1. Retatrutide doesn't arrive as two drugs mixed together. One compound is designed to act on all three.
GIP and GLP-1 are already familiar from current incretin medicines. Glucagon is the newer piece. Researchers study glucagon activity because it may influence how the body uses energy and how the liver handles fat. The phase 2 paper discusses this mechanism, and the ongoing trials are designed to test whether the third receptor adds real value. Here at MounjaBlog, we think that question matters more than any single headline.
As of the date of this post, the FDA, the EMA, and Anvisa have not approved retatrutide. Mounjaro and tirzepatide are the approved products in relevant markets, and approval status varies by country. Regulatory status can change, so check the agency databases listed below on the day you read this.
The Phase 2 Obesity Study
Jastreboff and colleagues published the phase 2 obesity trial in the New England Journal of Medicine in 2023. Participants had obesity but not diabetes. The study compared several retatrutide dose arms with placebo over 48 weeks. Exact sample sizes, per-arm numbers, and percent body weight change appear in the paper's results tables, so pull them from there rather than from news summaries.
The primary endpoint was percent change in body weight. Researchers also examined the dose-response pattern, which shows how weight change shifted as doses increased. Discontinuation rates matter just as much. A drug can only help if people stay on it, so the number who stopped early says a lot about tolerability.
The adverse events table lists gastrointestinal effects such as nausea, diarrhea, and vomiting. It also reports dysesthesia, meaning skin sensations like tingling or burning, along with heart rate increases. Check the incidence for each arm directly in that table.
The study has clear limits. It enrolled a relatively small group, ran for a relatively short time, and compared retatrutide with placebo rather than with tirzepatide. Nobody in it had diabetes, so the findings can't be assumed to apply to people who do.
The Type 2 Diabetes Phase 2 Work
Retatrutide has also been tested in people with type 2 diabetes. To find that work, search PubMed for retatrutide and type 2 diabetes phase 2, then confirm the journal, year, and design before you cite it. The outcomes to watch are change in HbA1c and change in body weight compared with placebo. Check the baseline HbA1c and the treatment duration too, because both shape how the numbers should be read.
Diabetes and obesity trials can't be compared directly. Participants with diabetes start with different glucose control and often take other medicines, such as metformin or insulin. A weight change in one population doesn't translate neatly to the other.
Phase 2 results are an early signal. These studies identify dose ranges and watch for safety patterns. They aren't designed to prove benefit. A promising result justifies larger testing, and that's all it does.
The Phase 3 TRIUMPH and Diabetes Programs
Lilly's phase 3 work includes the TRIUMPH program, which focuses on obesity and related conditions, and TRANSCEND-T2D, which focuses on type 2 diabetes. ClinicalTrials.gov lists each trial with its enrollment status, primary endpoint, and estimated completion date. Those fields change, so check them on the day you read this. Some trials list weight-related conditions such as knee osteoarthritis or sleep apnea as endpoints. Confirm that on the individual trial record.
A topline press release is a short company summary, often issued before the full analysis is complete. The numbers can shift once the complete dataset is reviewed. A peer-reviewed paper gives you the methods, subgroup results, and adverse event tables that press releases leave out.
The primary endpoint is the main outcome a trial was built to test. Secondary and exploratory outcomes can be interesting, but they carry less weight. Before getting excited about a headline, ask what the primary endpoint was and whether the trial met it.
Safety Signals and What Is Still Unknown
Phase 2 reported gastrointestinal effects, dysesthesia, and heart rate increases. Small, short trials can't capture rare events or long-term effects. That limit applies to almost any new drug, which is why phase 3 programs enroll more people for longer.
The tirzepatide label offers a useful comparison. The US prescribing information, available on DailyMed, carries a boxed warning for thyroid C-cell tumors, a class warning for incretin-based medicines. Tirzepatide is contraindicated in people with a personal or family history of medullary thyroid carcinoma or multiple endocrine neoplasia syndrome type 2. The label also covers pancreatitis, gallbladder disease, and hypoglycemia, especially when the drug is combined with insulin or sulfonylureas. Any warnings for retatrutide will depend on what regulators decide after reviewing its own data.
Talk with your prescriber about any side effect or safety question. Never self-dose. Avoid unapproved products from online sellers too, since their contents and doses can't be verified.
What This Means for People Using Mounjaro Today
Nothing changes for people taking tirzepatide because of these studies. Don't stop, skip, or adjust a dose based on trial news. Your plan depends on your health history and your prescriber's judgment.
No head-to-head trial comparing retatrutide with tirzepatide had been published at the time of writing. Verify that before relying on it, since results can appear at any time. Without that comparison, nobody can say whether retatrutide performs better, similarly, or worse.
Any future approval would follow regulatory review by agencies such as the FDA, EMA, and Anvisa. It would also require safety data from longer studies, a defined indication for a specific population, and labeling that explains risks and dosing. Each step takes time.
Bring questions about future options to your healthcare team, and ask what would change the plan if your situation shifts. Keeping track of your current options is easier with reliable reading, and our tirzepatide guides on MounjaBlog cover dosing questions, side effects, and what to ask at your next visit.
How to Keep Up With the Evidence
A few sources do most of the work here.
- ClinicalTrials.gov trial pages and PubMed alerts, which track new registrations, enrollment changes, and publications.
- Lilly press releases, quarterly investor reports, and the FDA, EMA, and Anvisa websites, which cover company updates and regulatory decisions.
Check the publication date of every article you read. Be cautious with headlines that give a percentage without context, because the baseline, comparator, population, and time frame all shape what that number means. The MounjaBlog team will update this post when major results or regulatory decisions appear.
FAQ
Is retatrutide approved anywhere?
As of the date of this post, the FDA, EMA, and Anvisa have not approved it. Check their databases for current status, since it can change.
Is retatrutide better than tirzepatide?
That isn't known yet. No head-to-head trial comparing the two had been published at the time of writing.
Should I switch to retatrutide when it becomes available?
Don't plan a switch based on news coverage. Talk with your prescriber about your current treatment and any future options.
Sources
- Triple-Hormone-Receptor Agonist Retatrutide for Obesity: A Phase 2 Trial (Jastreboff et al., New England Journal of Medicine, 2023)
- ClinicalTrials.gov
- PubMed
- Eli Lilly and Company Investor Relations
- U.S. Food and Drug Administration
- European Medicines Agency
- Anvisa, Agência Nacional de Vigilância Sanitária
- DailyMed: Mounjaro (tirzepatide) prescribing information
Disclaimer: This content is for informational purposes only and does not replace professional medical advice. Always consult your doctor before starting, changing or stopping any treatment.
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