Cardivo guides

What is retatrutide? How the "triple G" weight-loss drug works

Updated October 30, 2026 · Wellness education, not medical advice

Key takeaways

Retatrutide — often shortened to "reta" — is an investigational once-weekly injection from Eli Lilly, code name LY3437943.
It is a triple agonist: one molecule that activates GIP, GLP-1 and glucagon receptors, which is why it's nicknamed "triple G".
In the Phase 3 TRIUMPH-1 trial, the highest dose led to an average 28.3% weight loss at 80 weeks.
As of October 2026 it is not approved anywhere and has no brand name; Lilly plans to file with the FDA in early 2027.

Retatrutide in plain words

Retatrutide is a lab-made peptide — a short chain of amino acids — designed to imitate three hormones your gut and pancreas release around meals. It is injected under the skin once a week, like the newer weight-loss and diabetes medicines you may already know, such as semaglutide (Ozempic, Wegovy) and tirzepatide (Mounjaro, Zepbound). What makes retatrutide different is that it acts on three hormone receptors at once instead of one or two. That is why people searching for it often call it "reta", "triple G" or a "GLP-3", even though the last term isn't an official scientific name. Eli Lilly is developing it mainly for obesity and overweight, and it is also being tested in type 2 diabetes, knee osteoarthritis pain, obstructive sleep apnea, and kidney and heart conditions linked to excess weight.

The generic name is retatrutide (sometimes misspelled retatrutide, retratutide, retatrutid or "retaglutide" in searches); in Spanish and Portuguese it is retatrutida, in Japanese レタトルチド, and in Chinese 瑞他鲁肽. Because it has not been approved yet, there is no brand name. Any product sold online as "reta", "reta pen" or "retatrutide peptide" today is not the Lilly medicine — more on that in our guide to retatrutide FDA approval and availability.

How does retatrutide work? The three hormones

GLP-1 (glucagon-like peptide-1) is the hormone behind semaglutide. It tells the brain you are full, slows how fast the stomach empties, and helps the pancreas release insulin when blood sugar rises. In practice that means smaller portions feel satisfying and "food noise" — constant thoughts about eating — tends to quiet down. GIP (glucose-dependent insulinotropic polypeptide) is the second hormone added in tirzepatide. It also boosts insulin after meals and appears to improve how the body handles fat, and combining it with GLP-1 produced more weight loss than GLP-1 alone in earlier trials. Glucagon is the third and most unusual piece. Glucagon normally raises blood sugar, which sounds like the opposite of what you want, but at the right balance it also increases energy expenditure and pushes the liver to burn fat. The GLP-1 and GIP actions keep glucose in check while the glucagon action adds extra calorie burning and liver-fat reduction. Researchers think this combination is why retatrutide's weight loss has been larger than that of single- or dual-hormone drugs, and why it markedly reduced liver fat in studies of people with fatty liver disease.

What is retatrutide used for?

Right now retatrutide is only used inside clinical trials. Lilly's Phase 3 program, called TRIUMPH, enrolled thousands of adults with obesity or overweight plus at least one weight-related health problem. TRIUMPH-1, announced in May 2026, followed 2,339 adults without diabetes for 80 weeks: people on the 12 mg dose lost an average of 28.3% of their body weight (about 70 lb), compared with 2.2% on placebo, and nearly half of them lost 30% or more. TRIUMPH-2, published in The Lancet in September 2026, found an average loss of up to 20.8% in people with type 2 diabetes, along with A1C reductions of about 1.5 percentage points. Other trials are looking at whether that weight loss translates into less knee pain, better sleep apnea, healthier kidneys and fewer heart events. You can read the full numbers in retatrutide weight loss results.

Is retatrutide a peptide or a GLP-1?

Both, in a way. Chemically it is a peptide, which is why sellers market it as "retatrutide peptide" or "reta peptides". Pharmacologically it belongs to the same family as GLP-1 medicines — the incretin drugs — but it goes a step further by adding GIP and glucagon activity. That's why you'll see it described as a "GLP-1/GIP/glucagon receptor triple agonist". The word "peptide" on a website does not mean a product is natural, gentle or safe: insulin, semaglutide and tirzepatide are peptides too, and all of them are powerful prescription medicines.

Is retatrutide safe?

In trials, the most common side effects were digestive — nausea, diarrhea, constipation and vomiting — similar to other incretin drugs, plus a skin sensation called dysesthesia that was more common than with older medicines. Most were mild to moderate and eased as people stayed on a steady dose, but at the highest dose about 11% of TRIUMPH-1 participants stopped because of side effects. Long-term safety beyond about two years is still being studied. See the full list in retatrutide side effects. The bigger safety problem today is outside the trials: unregulated "research peptide" products of unknown strength and purity, which have been linked to serious harm — including reports of acute liver failure in Australia.

Retatrutide and your heart

Medicines in this family usually lower blood pressure and improve cholesterol and blood sugar as weight comes off, which is good for the heart. They also tend to raise resting heart rate by a few beats per minute; the Phase 2 retatrutide study reported a dose-dependent rise in heart rate that peaked around six months and then eased. Researchers are watching this closely in the ongoing heart-outcome trials. If you are taking any incretin medicine, it is sensible to know your baseline and watch the trend rather than single readings.

Track what matters while you work on your weight. Whatever medicine or plan you and your doctor choose, the numbers that change first are often your resting heart rate, your blood pressure and your blood sugar. Cardivo measures heart rate and HRV from your fingertip on the iPhone camera in about 30 seconds — no Apple Watch needed — and keeps cuff blood pressure, glucose and mood in one ad-free journal, with weekly trends and a PDF you can bring to your appointments.

This guide is general wellness education based on the public sources below. It is not medical advice, diagnosis, or treatment. Cardivo is not a medical device. If you think you are having a medical emergency, call 911.

Frequently asked questions

What is retatrutide?

Retatrutide is an investigational once-weekly injection from Eli Lilly that activates three hormone receptors — GIP, GLP-1 and glucagon. It is being studied for obesity, type 2 diabetes and related conditions and is not yet approved.

What does reta mean?

"Reta" is the common short name for retatrutide. It is also called "triple G" because it acts on GIP, GLP-1 and glucagon receptors.

What is the brand name of retatrutide?

There is no brand name yet because retatrutide has not been approved. Its development code is LY3437943.

How does retatrutide work?

It reduces appetite and slows stomach emptying through GLP-1, improves insulin response through GIP and GLP-1, and increases energy use and liver-fat burning through glucagon.

Sources

Cardivo is an ad-free iPhone app that reads heart rate and HRV from your fingertip on the camera in about 30 seconds — no Apple Watch needed — and keeps blood pressure, blood sugar, and mood in one journal you can share with your doctor as a PDF. Download on the App Store.