PeptidesInfo
Research

Retatrutide: The Triple-Hormone Weight-Loss Drug Still in Trials

Retatrutide is the next-generation weight-loss drug that hits three hormone targets at once. Trial results are striking, but it is not FDA-approved and cannot be legally compounded. Here is what the evidence actually shows.

Abstract lattice illustration for the retatrutide research analysis
Contents
  1. What retatrutide is
  2. What the trials actually found
  3. Side effects, so far
  4. The part that matters most right now
  5. The bottom line
  6. Where to go next

Key findings

  1. 1Retatrutide is a "triple agonist" — it activates three appetite and metabolism hormones (GIP, GLP-1 and glucagon), one more than tirzepatide and two more than semaglutide.
  2. 2In a 48-week phase 2 trial of 338 adults with obesity, the highest dose (12 mg) produced about 24% average weight loss — the largest reported for a weight-loss drug at the time.
  3. 3Positive phase 3 (TRIUMPH) topline results reported even larger loss (about 28% over 80 weeks), but the full data are not yet published or peer-reviewed.
  4. 4Side effects were mostly stomach-related (nausea, diarrhea) and happened mainly while the dose was being raised — similar to other incretin drugs.
  5. 5It is not FDA-approved and, unlike a shortage-era exception, cannot be legally compounded; products sold online as "retatrutide" are unapproved and unregulated.

Evidence level

Promising evidence

A published phase 2 randomized trial (NEJM, 2023) and positive phase 3 topline results show large weight loss, but retatrutide is still investigational, the full phase 3 data are not yet published, and long-term safety is still being studied.

Regulatory status

Investigational

Retatrutide is not FDA-approved for any use. It is in late-stage (phase 3) trials and has not yet been submitted for FDA approval. It cannot be legally used in compounded drugs.

Retatrutide keeps showing up in weight-loss headlines with numbers no drug has hit before. It is real, and the trial results are genuinely striking - but it is not something you can get at a pharmacy, and what is sold online under its name is a different story. Here is where the evidence actually stands.

What retatrutide is

Retatrutide is an experimental drug from Eli Lilly, given as a weekly shot. Its standout feature is that it is a triple agonist - it switches on three of the body's hormone systems at once.

To see why that matters, line up the drugs people already know:

  • Semaglutide (Ozempic, Wegovy) acts on one pathway: GLP-1.
  • Tirzepatide (Mounjaro, Zepbound) acts on two: GIP and GLP-1.
  • Retatrutide acts on three: GIP, GLP-1, and glucagon.

An agonist is just a molecule that turns a receptor "on." GLP-1 and GIP are gut hormones that curb appetite and help control blood sugar. Glucagon is the newer addition here - at these doses it appears to nudge the body to burn more energy. The bet researchers are testing is simple: hit three targets, get more weight loss[1].

What the trials actually found

Phase 2 (published, peer-reviewed). In a randomized, placebo-controlled trial of 338 adults with obesity, people on the highest dose (12 mg) lost about 24% of their body weight over 48 weeks, compared with about 2% on placebo[1]. For context, that was the largest average weight loss reported for any obesity drug at the time it was published in 2023. This is the most reliable evidence we have, because it is a full trial that outside experts have reviewed.

Phase 3 (topline only, not yet published). Lilly has since reported early "topline" results from its large TRIUMPH trials. TRIUMPH-1 followed 2,339 adults with obesity but not diabetes for 80 weeks; the company reported average weight loss of about 28% on the top dose (12 mg)[2].

Here is the important caveat: those phase 3 numbers come from a company press release, not a full published study. Topline results are real data, but they are the summary the maker chooses to share before the complete results are reviewed and published. Treat them as promising signals, not the final word.

Side effects, so far

The side effects reported in the trials look a lot like the ones for semaglutide and tirzepatide: mostly stomach-related - nausea, diarrhea, constipation, vomiting. They were generally mild to moderate and happened mostly while the dose was being slowly raised[1].

Because retatrutide is newer and still in trials, there is less long-term safety data than for the approved drugs. That is a normal part of being investigational - it is not a red flag by itself, but it is a real limit on what anyone can promise.

The part that matters most right now

You cannot get retatrutide as an approved medicine, and you cannot get it legally compounded either.

  • It is not FDA-approved for any use. It is still in phase 3 trials and has not been submitted to the FDA, so a real prescription version is likely still a while away[2].
  • It cannot be legally compounded. During drug shortages, pharmacies were briefly allowed to make copies of semaglutide and tirzepatide. Retatrutide never qualified for that - the FDA says it cannot be used in compounding, and it has warned telehealth companies and ingredient suppliers against selling it[3].

The bottom line

Retatrutide may end up being the most effective weight-loss drug yet - the trial numbers are hard to ignore. But "may end up" is the key phrase. Today it is an investigational drug with strong early evidence, incomplete long-term data, and no legal way to obtain it outside a clinical trial. The honest reading: worth watching closely, not worth chasing on the grey market.

Where to go next

Frequently asked questions

What is retatrutide?
Retatrutide is an experimental weight-loss drug from Eli Lilly. It is a 'triple agonist,' meaning it activates three hormone pathways at once - GIP, GLP-1 and glucagon - to reduce appetite and affect how the body uses energy.
Is retatrutide FDA-approved?
No. Retatrutide is still in phase 3 clinical trials, is not approved for any use, and has not yet been submitted for FDA approval.
How much weight did people lose on retatrutide?
In a 48-week phase 2 trial, adults on the highest dose lost about 24% of their body weight on average. Company-reported phase 3 topline results were even higher (about 28% over 80 weeks), but that full data set has not been published yet.
How is retatrutide different from Ozempic or Mounjaro?
Semaglutide (Ozempic, Wegovy) works on one hormone pathway (GLP-1). Tirzepatide (Mounjaro, Zepbound) works on two (GIP and GLP-1). Retatrutide adds a third, glucagon - which is the main reason researchers are studying whether it can produce larger weight loss.
Can I buy retatrutide now?
Not legally as a medicine - it is not approved, and unlike some drugs during shortages, it cannot be compounded. Anything sold online as 'retatrutide,' including vials labeled 'research use only,' is unapproved and unregulated, so its contents and safety are unknown.

References

Numbered in order of first use. Study type is shown for every source; see our methodology for how we rank evidence.

  1. 1.

    Triple-Hormone-Receptor Agonist Retatrutide for Obesity - A Phase 2 Trial New England Journal of Medicine (Jastreboff et al.), 2023.

    Randomized controlled trialAdults with obesity (BMI 30 or higher, or 27 or higher with a weight-related condition)n = 338

    Result: Randomized, double-blind, placebo-controlled phase 2 trial in 338 adults with obesity. At 48 weeks the 12 mg dose produced a least-squares mean weight reduction of 24.2% vs 2.1% for placebo. Most adverse events were mild-to-moderate gastrointestinal, mainly during dose escalation.

    ↑ back to text
  2. 2.

    TRIUMPH-1: A Study of Retatrutide (LY3437943) in Participants With Obesity or Overweight (NCT05929066) ClinicalTrials.gov (Eli Lilly and Company), 2026.

    Trial registry

    Result: Phase 3 randomized, double-blind, placebo-controlled trial in 2,339 adults with obesity or overweight (without type 2 diabetes), treated once weekly for 80 weeks. Company-reported topline weight loss at week 80 was 19.0%, 25.9%, and 28.3% for the 4, 9, and 12 mg doses; full peer-reviewed results are pending.

    ↑ back to text
  3. 3.

    FDA's Concerns with Unapproved GLP-1 Drugs Used for Weight Loss U.S. Food and Drug Administration, 2026.

    Regulatory source

    Result: FDA states retatrutide is not approved and cannot be used in compounding; it has warned telehealth companies and ingredient distributors against selling it, and warns against products labeled 'for research purposes' that are sold for human use.

    ↑ back to text

Review status: Editorially reviewed against primary sources. This article was fact-checked against the primary sources listed in the references by our editorial team, and it has not been reviewed by a licensed clinician. It is educational content, not medical advice. Read our editorial policy and methodology. Spotted an error? Tell us.

retatrutideGLP-1GIPglucagonweight lossincretinEli Lilly

Continue researching

Related analyses, profiles, and research areas

Recommendations are ranked by shared peptides, research areas, evidence level, and topic tags — not by popularity.

Peptide profiles

Benefits5 min read

GLP-1 Benefits Beyond Weight Loss: Heart, Kidney, Liver, and Sleep

Semaglutide and tirzepatide have now shown benefits in cardiovascular events, kidney disease, liver disease, heart failure and sleep apnoea — each in its own trial, in its own population. Here is what each one actually demonstrated.

Research analysis5 min read

GLP-1 Peptides: Established Uses Versus Emerging Research

Semaglutide and tirzepatide are the best-evidenced peptides in medicine — for specific uses. We separate the approved indications with large trials from the emerging research (kidney, liver, heart failure, sleep apnoea, Alzheimer's) and the open questions about regain, muscle loss and compounded products.