GLP-3 vs GLP-1: Triple vs Single Agonist Comparison Chart (2026)

What Is "GLP-3"? Clearing Up the Terminology

"GLP-3" has no official pharmacological meaning. There is no GLP-3 receptor and no FDA drug category by that name. It is a consumer-facing label, popularized by media and some clinics, for the triple-agonist drug class, most commonly retatrutide (developed by Eli Lilly as LY3437943). The correct technical terms are "triple-agonist" or "GLP-1/GIP/glucagon receptor agonist." A 2025 peer-reviewed review of triple-agonist therapies for obesity describes the mono-, dual-, and triple-agonist classes without ever using "GLP-3" as a formal classification, which confirms it sits outside standard pharmacology.

GLP-1 and GLP-2 are both real endogenous gut hormones. GLP-1 (glucagon-like peptide-1) is the pathway behind every drug in this article. GLP-2 (glucagon-like peptide-2) regulates intestinal growth and barrier function and has no current obesity drug class built around it. Some sources loosely call tirzepatide a "GLP-2" drug, which is incorrect: tirzepatide is a GIP/GLP-1 dual agonist and has nothing to do with the GLP-2 hormone. Throughout this article, "GLP-3" appears in quotation marks to signal it is an informal term, not a receptor.

Why the Term "GLP-3" Caught On

The shorthand spread because it is intuitive. People already knew "GLP-1" from Ozempic and Wegovy, so "GLP-3" reads as a natural next generation, even though the number refers to how many receptors are hit, not a new hormone. Science and general news outlets used the framing when retatrutide's Phase 2 results landed, and it stuck. Our own name reflects that usage. The label is convenient marketing, but the science is precise: retatrutide is a triple-receptor agonist, not a drug targeting some "GLP-3."

The Three Generations of GLP-Based Obesity Drugs (Comparison Chart)

Each generation adds a receptor target, and trial weight loss has risen with each addition. The chart below sets the GLP-1 mono-agonist, GIP/GLP-1 dual-agonist, and triple-agonist ("GLP-3") classes side by side on the seven dimensions people ask about most.

Reading the Chart: What the Numbers Actually Mean

Percentages are easier to picture as pounds. Take a 220-pound starting weight as a round example and apply each trial's mean reduction at its top studied dose: semaglutide's 14.9% is about 33 pounds, tirzepatide's 20.9% is about 46 pounds, and retatrutide's 24.2% is about 53 pounds. That arithmetic is just the percentage applied to one example weight, not a prediction. Individual results vary widely, the trials are not directly comparable, and retatrutide's figure comes from Phase 2 data only.

GLP-3 vs GLP-1: Mechanism Differences That Explain the Weight Loss Gap

Every drug here mimics natural gut hormones. The difference is how many receptors each one switches on. More targets has meant more weight loss in trials, and each receptor contributes a distinct effect.

GLP-1 Receptor Agonism (All Three Classes Have This)

GLP-1 receptor activation slows gastric emptying, reduces appetite, stimulates insulin secretion, and suppresses glucagon in the fed state. Every class in this comparison shares this pathway. It is the foundation that makes semaglutide work on its own, and the shared base that tirzepatide and retatrutide build on top of.

GIP Receptor Agonism (Tirzepatide and Retatrutide)

Adding the GIP receptor enhances insulin secretion, influences fat metabolism and storage, and may improve how the body responds to GLP-1 (Coskun et al., Cell Metab 2022). Tirzepatide and retatrutide both activate GIP; semaglutide does not. This is the step from a single-receptor drug to a dual agonist, and it correlates with the jump from 14.9% to 20.9% in the respective trials.

Glucagon Receptor Agonism (Retatrutide Only)

The glucagon receptor is the layer unique to the triple-agonist class. Glucagon receptor activation drives thermogenesis and energy expenditure, promotes lipolysis, and at low doses raises hepatic glucose output. Discovery and proof-of-concept work published in Cell Metabolism in 2022 detailed retatrutide's pharmacology, including a half-life of roughly 6 days and high subcutaneous bioavailability, which support once-weekly dosing. This third target is what separates "GLP-3" from the dual agonists.

GLP-3 vs GLP-1: Weight Loss Outcomes From the Trials

Three separate trials anchor the numbers. They are not interchangeable, but together they show the trend that each added receptor target has tracked with larger mean weight loss.

Semaglutide (GLP-1 Mono): 14.9% at 68 Weeks

In the STEP 1 trial, semaglutide 2.4mg produced 14.9% average body weight loss over 68 weeks. It is FDA-approved, widely available as Wegovy and Ozempic, and the only drug in this group with a cardiovascular outcome benefit shown in the SELECT trial in 2023, the first weight-loss drug to demonstrate one. Semaglutide is the established benchmark every newer class is measured against.

Tirzepatide (Dual Agonist): 20.9% at 72 Weeks

SURMOUNT-1 showed tirzepatide 15mg producing 20.9% mean body weight loss at 72 weeks. There is also a direct head-to-head: in the SURMOUNT-5 obesity trial, tirzepatide reached 20.2% versus 13.7% for semaglutide 2.4mg over 72 weeks. That head-to-head is a tirzepatide-versus-semaglutide comparison, not a stand-in for the primary SURMOUNT-1 figure. Tirzepatide is FDA-approved and commercially available as Zepbound and Mounjaro.

Retatrutide (Triple Agonist / "GLP-3"): 24.2% at 48 Weeks

The Phase 2 trial published in the New England Journal of Medicine in 2023, with 338 participants over 48 weeks, showed retatrutide 12mg producing 24.2% mean body weight loss, the highest figure recorded for an obesity drug to date (Jastreboff et al., NEJM 2023). It is not FDA-approved: Phase 3 results have been reported since December 2025, and Lilly plans to file with the FDA in Q1 2027. In the US, lawful access is limited to a clinical trial or Lilly's narrow expanded access program (NCT07629401). Research-peptide sellers also offer it, but the FDA calls products falsely labeled "for research purposes" illegally sold unapproved drugs. A fuller side-by-side sits in our retatrutide vs tirzepatide head-to-head breakdown and our retatrutide vs semaglutide comparison.

Side Effects: Is "GLP-3" Harder to Tolerate?

All three classes share the same core gastrointestinal side-effect profile: nausea, diarrhea, constipation, and vomiting. That makes sense, since every one of them activates the GLP-1 receptor. Those effects are dose-dependent and tend to ease as the body adjusts during titration.

For retatrutide specifically, nausea affected 45% of the 12mg group versus 11% on placebo in the Phase 2 trial's posted results (Jastreboff et al., NEJM 2023), with most events mild to moderate. In the Phase 3 trial TRIUMPH-1 (Jastreboff et al., NEJM 2026; adults with obesity or overweight, without diabetes), nausea affected 28.6% to 42.4% across the 4mg to 12mg doses versus 14.8% on placebo. There is no head-to-head safety trial across the three classes, so a precise side-by-side side-effect table is not possible without inventing data. The pattern across the board is the same: symptoms peak during dose escalation and generally settle at each maintenance level.

FDA Status and Availability: The Practical Difference

For most people the deciding factor is access, not mechanism. Can you actually get the drug legally and predictably?

• Semaglutide: FDA-approved, prescription only. Available branded as Wegovy and Ozempic. Compounded versions exist in a shifting legal gray area.
• Tirzepatide: FDA-approved, prescription only. Available branded as Zepbound and Mounjaro. Compounded versions exist in the same gray area.
• Retatrutide: Not FDA-approved. Investigational. The FDA states retatrutide cannot be used in compounding under US federal law, so compounding pharmacies cannot lawfully supply it. In the US, the routes available today are a clinical trial or Lilly's expanded access program (ClinicalTrials.gov NCT07629401), which a doctor must request, for adults with a BMI of 35 or more whose obesity has not responded to the highest available dose of current weight-loss treatment, who have two or more serious obesity-related complications, and who cannot join a trial. Lilly provides the product at no cost, but the doctor must apply to the FDA as sponsor of a patient-specific investigational new drug (IND) application and obtain IRB approval (Lilly Medical). Most retatrutide Phase 3 trials are no longer enrolling; check ClinicalTrials.gov for open studies. Research-peptide products are not FDA-regulated and carry higher uncertainty about identity, purity, and dose.

For more on the retatrutide access picture specifically, see our coverage of retatrutide availability, compounded retatrutide, and whether retatrutide is FDA-approved.

Which Class Is Right for You?

None of this is a recommendation, and the choice is one to make with a clinician who knows your history. That said, the published evidence groups people into a few common situations. Match yours below, then take it to your prescriber.

• You have an FDA prescription and want a proven, approved option. Semaglutide or tirzepatide are the two approved classes. Both have completed Phase 3 programs and are commercially available. Tirzepatide showed the larger trial figure of the two (20.9% in SURMOUNT-1 versus 14.9% for semaglutide in STEP 1), though the trials differ in design.
• You prioritize cardiovascular-benefit evidence. Semaglutide is the only drug in this comparison with a demonstrated cardiovascular outcome benefit, shown in the SELECT trial in 2023. If reducing cardiovascular risk is the priority alongside weight loss, that evidence sits with semaglutide today.
• You want the largest trial weight loss reported and accept investigational status. Retatrutide produced 24.2% mean body weight loss in its Phase 2 trial over 48 weeks, the highest figure recorded for an obesity drug to date. It is not FDA-approved, Phase 3 data are pending, and any use would be under a clinician's supervision through a trial or a non-FDA-regulated channel that carries real uncertainty about identity, purity, and dose.
• You want predictable, regulated supply above maximum effect. The two approved classes are the clear pick here. Retatrutide has no FDA-regulated supply chain, so identity and dosing are not guaranteed outside a clinical trial or Lilly's expanded access program. Access reliability is often what decides this in practice, not the trial percentage.
• Dosing cadence and half-life matter to your routine. All three are once-weekly injections, with half-lives of roughly 7 days for semaglutide, 5 days for tirzepatide, and 6 days for retatrutide. The practical schedule is similar across all three, so this rarely drives the decision on its own.

GLP3Planner: Tracking All Three on One Calculator

GLP3Planner is a free pharmacokinetic calculator that uses exponential decay modeling, and it supports retatrutide, tirzepatide, and semaglutide on the same platform (along with the Mounjaro, Zepbound, Ozempic, and Wegovy brands). Whether you are reading about the GLP-1 mono-agonist class or the triple-agonist "GLP-3" class, you can compare half-life decay curves, build a multi-tier dose schedule, and track vial usage across any of the three compound classes in one place.

Free features include dose visualization, multi-tier schedule building, vial tracking, weight tracking, schedule sharing via a token link, and CSV export. The triple-agonist mechanism behind retatrutide is covered in depth in our triple agonist mechanism explained guide, and newcomers can start with our getting started with GLP-1 agonists guide.

Video: A Doctor Explains the Triple-Agonist Difference

In this explainer, Dr. Alex Tatem walks through retatrutide's triple-receptor mechanism and how it compares to GLP-1 single-agonist drugs like semaglutide.

Frequently Asked Questions