What is retatrutide and how is it different from GLP-1/GIP medications?

Retatrutide is an investigational, once-weekly injectable medication for obesity that activates three metabolic hormone receptors: GLP-1, GIP, and glucagon. This differs from semaglutide (GLP-1 only) and tirzepatide (GLP-1/GIP), which target one or two pathways.

How does retatrutide work (GLP-1, GIP, and glucagon receptor activity)?

Retatrutide is a triple-receptor agonist. GLP-1 activity can reduce appetite and slow gastric emptying, GIP activity may enhance insulin response and satiety signaling, and glucagon receptor activity may increase energy expenditure and fat oxidation. This mechanistic rationale may contribute to strong trial results, but it is not definitive proof of superiority.

Is retatrutide a “GLP-3” medication?

No. “GLP-3” is not a recognized hormone or pharmacologic class. The term is marketing shorthand sometimes used to describe medications like retatrutide that affect three metabolic targets (GLP-1, GIP, and glucagon), but there is no “GLP-3” hormone or “GLP-3 receptor.”

Is retatrutide more effective than semaglutide or tirzepatide for weight loss?

In separate clinical trials, retatrutide has shown numerically greater average weight loss at 48 weeks than semaglutide or tirzepatide achieved in their respective trials. However, because there are no head-to-head randomized comparisons and trial designs differ, retatrutide cannot be labeled definitively “more effective” by accepted clinical research standards.

Does retatrutide cause more side effects than tirzepatide?

Not conclusively. In the NEJM phase 2 retatrutide trial, the most common side effects were gastrointestinal (nausea, vomiting, diarrhea), typically mild to moderate and most frequent during dose escalation, with higher doses showing more GI effects and transient heart-rate increases. Because adverse-event rates have not been directly compared in head-to-head trials, it is not scientifically accurate to conclude retatrutide causes more side effects than tirzepatide—only that side effects appear comparable in type and dose-dependent.

Has retatrutide been linked to any unusual side effects in later studies?

Later-phase studies have reported abnormal skin sensations (dysesthesia) more frequently at higher doses of retatrutide. Similar sensations have been reported rarely with other incretin-based therapies, but the higher reported rates with retatrutide are under active evaluation as more peer-reviewed data become available.

Is retatrutide FDA-approved for weight loss?

No. Retatrutide is not FDA-approved for weight loss. It remains investigational with phase 3 clinical trials ongoing, and no FDA-approved indication exists at this time. FDA approval has not yet been granted, and the timing of any regulatory decision is not currently known.

Should I wait for retatrutide instead of starting semaglutide or tirzepatide?

For most patients, waiting is not medically advisable. Semaglutide and tirzepatide are FDA-approved with well-established evidence, and delaying treatment can prolong exposure to obesity-related risks such as type 2 diabetes, cardiovascular disease, and fatty liver disease. If retatrutide becomes FDA-approved in the future and is appropriate for you, your treatment plan can be adjusted at that time.

Do clinics offer retatrutide, and why don’t you prescribe it yet?

Some patients may see retatrutide advertised by clinics, marketed by vendors, or sold as “research-grade” peptides, but availability does not mean a medication is FDA-approved or appropriate for routine prescribing. Retatrutide has not completed the full approval process, long-term safety and outcomes are still being defined, and the FDA has stated retatrutide is not FDA-approved and is not eligible for pharmacy compounding under current federal regulations. We prescribe based on evidence, dosing standards, safety characterization, and regulatory clarity, using FDA-approved medications—or carefully selected compounded therapies when legally appropriate—until retatrutide meets criteria for routine clinical use.

Retatrutide vs Tirzepatide vs Semaglutide: Which Is Best for Weight Loss?

Joshua Silva, MD

Jan 8

6 min read

Updated: Sep 22

Medically authored by Joshua Silva, MD | Evidence-Based Weight Loss at Potere Health MD

Last clinically updated: September 2026

Quick answer: Retatrutide is a once-weekly weight-loss medication being developed by Eli Lilly. It targets three hormone receptors—GLP-1, GIP, and glucagon. In the Phase 3 TRIUMPH-1 trial, the highest dose produced 28.3% average weight loss at 80 weeks.¹ That is more than the average weight loss reported with tirzepatide or semaglutide, although retatrutide has not yet completed a direct head-to-head obesity trial against tirzepatide.

What Is Retatrutide and How Does It Work?

Retatrutide is an investigational medication being studied for obesity and related conditions. Like semaglutide and tirzepatide, it is given as a once-weekly injection.

The main difference is that retatrutide targets three hormone receptors instead of one or two:⁶

Medication	Hormone Targets
Semaglutide	GLP-1
Tirzepatide	GLP-1 + GIP
Retatrutide	GLP-1 + GIP + glucagon

GLP-1 helps reduce appetite and slows stomach emptying. GIP affects insulin response, appetite, and metabolism. Glucagon can increase energy use and fat metabolism.

Researchers believe combining these three pathways may help explain the unusually large amount of weight loss seen with retatrutide.⁶

Simple diagram showing retatrutide acting on GLP-1, GIP, and glucagon receptors (triple agonist), addressing the common question of whether it is a “GLP-3” medication

Is Retatrutide a GLP-3?

Not technically. “GLP-3” has become a popular nickname for retatrutide because it targets three hormone receptors.

There is no GLP-3 hormone or GLP-3 receptor. Retatrutide is more accurately described as a triple hormone receptor agonist because it targets GLP-1, GIP, and glucagon receptors.⁶

How Much Weight Can You Lose on Retatrutide?

The newest Phase 3 results have shown substantial weight loss.

In the TRIUMPH-1 trial, adults with obesity or overweight without diabetes lost an average of:¹

19.0% with retatrutide 4 mg
25.9% with retatrutide 9 mg
28.3% with retatrutide 12 mg
2.2% with placebo

At the 12 mg dose, participants lost about 70 pounds on average, from an average starting weight of about 249 pounds.

About 45% of participants taking 12 mg lost at least 30% of their starting body weight.¹

Participants with a starting BMI of 35 or greater who continued into an extension of the study lost an average of 30.3% at 104 weeks with the 12 mg dose.¹

These are among the largest average weight-loss results reported with a medication for obesity.

Retatrutide vs Tirzepatide: Which Is Better for Weight Loss?

So far, retatrutide has produced greater average weight loss in clinical trials. However, we do not yet have results from a completed trial directly comparing retatrutide with tirzepatide.

The best current results are:

Medication	Average Weight Loss	Time
Retatrutide	28.3%	80 weeks
Tirzepatide	20.2%	72 weeks
Semaglutide	13.7%	72 weeks

Retatrutide's 28.3% result comes from TRIUMPH-1.¹

The tirzepatide and semaglutide numbers come from SURMOUNT-5, where the two medications were directly compared. Tirzepatide produced 20.2% average weight loss compared with 13.7% with semaglutide at 72 weeks.²

The important point is that the retatrutide number comes from a different trial. It is therefore encouraging, but it does not yet prove that retatrutide works better than tirzepatide.

That question is being studied directly in TRIUMPH-5, a Phase 3 trial comparing retatrutide with tirzepatide. The study has an estimated completion date of December 2026.⁵

Retatrutide vs Semaglutide: Which Is Better?

Based on current trial results, retatrutide appears likely to produce substantially more weight loss than semaglutide.¹˒²

Semaglutide targets GLP-1, while retatrutide targets GLP-1, GIP, and glucagon. The two medications have not yet been directly compared in a completed obesity trial, so the percentages should not be interpreted as meaning every patient would lose twice as much weight with retatrutide.

What Are the Side Effects of Retatrutide?

Retatrutide's most common side effects are similar to those seen with other GLP-1–based medications:¹

Nausea
Diarrhea
Constipation
Vomiting

Side effects are generally more common at higher doses. Earlier clinical research also found that gastrointestinal side effects were usually mild to moderate and could be reduced by starting at a lower dose and increasing gradually.⁶

Earlier studies also found temporary increases in heart rate. These peaked during treatment and then declined.⁶

Does Retatrutide Cause Skin Sensitivity or Tingling?

Researchers have also reported dysesthesia, which can cause unusual skin sensations such as tingling, burning, altered sensation, or increased skin sensitivity.

In TRIUMPH-1, dysesthesia occurred in about 5% of patients taking 4 mg and about

12% taking 9 mg or 12 mg, compared with less than 1% taking placebo.¹

Most cases were mild to moderate, and most went away while patients were still taking retatrutide. Most patients were able to continue treatment.¹

Is Retatrutide FDA Approved?

No. Retatrutide is not FDA approved as of September 2026.⁴

Multiple Phase 3 trials have now reported positive results. Lilly says it plans to submit retatrutide to the FDA for U.S. approval in the first quarter of 2027.³

When Will Retatrutide Be Available?

There is no official retatrutide release date yet.

Lilly plans to submit retatrutide to the FDA in early 2027. The FDA would then review the application before the medication could be commercially launched as an approved treatment.³

Can You Get Retatrutide Now or Online?

Patients may already see products labeled as retatrutide advertised through wellness clinics, telehealth companies, online sellers, and pharmacies. However, there is currently no FDA-approved retatrutide available for routine prescribing.

The FDA currently states that retatrutide cannot be used in compounding under federal law.⁴

This can understandably be confusing when a product is prescribed by a physician or comes from a licensed pharmacy. Pharmacy licensure does not change retatrutide's current federal regulatory status.

Patients should be especially cautious with products sold directly online as “research peptides,” “research-grade retatrutide,” or “not for human consumption.” The FDA has specifically warned companies about marketing unapproved retatrutide products.⁴

Should I Wait for Retatrutide?

Probably not if you need weight-loss treatment now.

Semaglutide and tirzepatide are already available and have extensive clinical trial evidence. Tirzepatide has also now been directly compared with semaglutide and produced greater average weight loss.²

Retatrutide may eventually become another important option, particularly for people who need greater weight loss or have not reached their goals with existing medications.

From a medical standpoint, the largest weight-loss percentage is not the only factor that matters. Medication source, dosing, side effects, safety, regulatory status, cost, and the individual patient's needs all play a role in choosing treatment.

At Potere Health MD, we follow emerging medications such as retatrutide closely. If it becomes an appropriate treatment option in the future, its role can be considered alongside the medications already available.

What Is the Bottom Line on Retatrutide?

Retatrutide may become the most effective weight-loss medication developed so far.

Phase 3 research has shown up to 28.3% average weight loss at 80 weeks, with about 45% of participants taking the highest dose losing at least 30% of their starting body weight.¹

Its three-receptor mechanism may help explain why its weight-loss results have been so strong. But retatrutide is not yet FDA approved, and we are still waiting for the direct comparison with tirzepatide.

For now, semaglutide and tirzepatide remain established treatment options, while retatrutide is one of the most important new obesity medications to watch.

At Potere Health MD, we follow new obesity research closely so patients throughout Utah can make treatment decisions based on current medical evidence rather than marketing or social-media claims.

Disclaimer:

This article is for educational purposes only and is not a substitute for medical advice.

About the Author

Dr. Joshua Silva, MD, is a licensed physician and Medical Director of Potere Health MD. He earned his medical degree from the University of Hawaiʻi John A. Burns School of Medicine and completed residency training in Occupational and Environmental Medicine at the University of Utah, where he also earned a master’s degree in Occupational Health. He later completed a Master of Business Administration with an emphasis in health care administration at Ohio University.

Dr. Silva specializes in evidence-based weight management, including GLP-1 and GIP therapies such as semaglutide and tirzepatide. He provides in-person and virtual care for patients in Salt Lake City, St. George, and Cedar City, Utah.

Sources:

1. Eli Lilly and Company. Lilly's triple agonist, retatrutide, delivered powerful weight loss in pivotal phase 3 obesity trial. Published May 21, 2026. Accessed September 4, 2026.

2. Aronne LJ, Bade Horn D, le Roux CW, et al. Tirzepatide as compared with semaglutide for the treatment of obesity.N Engl J Med. 2025;393(1):26-36. doi:10.1056/NEJMoa2416394.

3. Eli Lilly and Company. Lilly's triple agonist, retatrutide, successful in two additional phase 3 obesity trials, delivering significant improvements in weight and A1C. Published July 23, 2026. Accessed September 4, 2026.

4. US Food and Drug Administration. FDA's concerns with unapproved GLP-1 drugs used for weight loss. Accessed September 4, 2026.

5. ClinicalTrials.gov. A study of retatrutide (LY3437943) compared to tirzepatide (LY3298176) in adults who have obesity (TRIUMPH-5). ClinicalTrials.gov identifier NCT06662383. Updated April 13, 2026. Accessed September 4, 2026.

6. Jastreboff AM, Kaplan LM, Frías JP, et al. Triple-hormone-receptor agonist retatrutide for obesity—a phase 2 trial.N Engl J Med. 2023;389(6):514-526. doi:10.1056/NEJMoa2301972.