GLP-1 Receptor Agonists Compared: Semaglutide vs Tirzepatide vs Retatrutide

The Evolution From Single to Triple Receptor Targeting

The development of GLP-1 receptor agonists represents one of the most significant advances in metabolic research over the past decade. What began with single-receptor compounds like semaglutide has rapidly evolved into dual and triple agonists that target multiple metabolic pathways simultaneously — each generation producing larger effect sizes in clinical trials.

This article compares the published clinical trial data for the five most studied compounds in this class: semaglutide, tirzepatide, retatrutide, survodutide, and mazdutide. The comparison focuses on what the numbers actually show — trial design, weight loss percentages, receptor mechanisms, and evidence levels. No hype — just science.

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1. Semaglutide — The Single Agonist Benchmark

What It Is

Semaglutide is a GLP-1 receptor agonist originally developed for type 2 diabetes (marketed as Ozempic) and later approved for chronic weight management (marketed as Wegovy). It targets a single receptor — GLP-1 — and remains the most extensively studied compound in this class.

Trial Data

The STEP program produced the foundational evidence base:

• STEP 1 (Wilding et al., 2021, NEJM): 2.4 mg subcutaneous, 1,961 adults with obesity, 68 weeks — 14.9% mean body weight loss vs 2.4% placebo
• STEP 2 (Davies et al., 2021, The Lancet): Type 2 diabetes patients — 9.6% weight loss at 68 weeks
• STEP 3 (Wadden et al., 2021, JAMA): With intensive behavioral therapy — 16.0% weight loss
• STEP 5 (Garvey et al., 2022, Nature Medicine): Long-term, 104 weeks — 15.2% sustained weight loss
• SELECT (Lincoff et al., 2023, NEJM): 20% reduction in major adverse cardiovascular events

Mechanism Advantage

Semaglutide works by mimicking the incretin hormone GLP-1, which reduces appetite, slows gastric emptying, and enhances insulin secretion. Its acylation modification gives it a half-life of approximately 7 days, allowing once-weekly administration. The SELECT trial established cardiovascular benefits beyond weight loss — a significant regulatory milestone.

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2. Tirzepatide — The Dual Agonist

What It Is

Tirzepatide is a dual GIP and GLP-1 receptor agonist developed by Eli Lilly. It is marketed as Mounjaro (for type 2 diabetes) and Zepbound (for weight management, FDA-approved November 2023). By adding GIP receptor activation on top of GLP-1, tirzepatide demonstrated that multi-receptor targeting could surpass single-agonist results.

Trial Data

The SURMOUNT program established the dual-agonist evidence base:

• SURMOUNT-1 (Jastreboff et al., 2022, NEJM): 2,539 adults without diabetes, 72 weeks:
  • 5 mg dose: 15.0% weight loss
  • 10 mg dose: 19.5% weight loss
  • 15 mg dose: 20.9% weight loss
  • Placebo: 3.1% weight loss
• SURMOUNT-2 (Garvey et al., 2023, The Lancet): Type 2 diabetes patients — 14.7% at 15 mg, 72 weeks
• SURMOUNT-3: With intensive lifestyle intervention — up to 26.6% body weight reduction

Mechanism Advantage

Tirzepatide’s addition of GIP receptor agonism enhances insulin sensitivity and glucose-dependent insulin secretion beyond what GLP-1 alone provides. The GIP pathway also appears to contribute independently to fat metabolism, though the precise mechanism is still being characterized. The 20.9% result at the highest dose represented a significant improvement over semaglutide’s 14.9%.

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3. Retatrutide — The Triple Agonist

What It Is

Retatrutide (LY3437943) is a triple agonist that simultaneously activates GIP, GLP-1, and glucagon receptors. Developed by Eli Lilly, it adds glucagon receptor activation to the dual GIP/GLP-1 approach of tirzepatide — targeting a third metabolic pathway that increases energy expenditure and promotes fat oxidation.

Trial Data

A Phase 2 trial published in The New England Journal of Medicine (Jastreboff et al., 2023) enrolled 338 adults with obesity:

• Highest dose (12 mg): 24.2% mean body weight reduction at 48 weeks
• This was the largest weight reduction reported for any anti-obesity compound in a Phase 2 trial at the time of publication
• Phase 3 trials (the TRIUMPH program) are currently underway to confirm these findings in larger populations

Mechanism Advantage

The glucagon receptor component is what distinguishes retatrutide from tirzepatide. Glucagon activation increases hepatic glucose output and energy expenditure — the body burns more calories even at rest. This thermogenic effect, combined with appetite suppression (GLP-1) and enhanced insulin sensitivity (GIP), creates a three-pronged approach that produced the highest weight loss numbers in the class.

Available for research: Retatrutide

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4. Survodutide — GLP-1 Meets Glucagon

What It Is

Survodutide (BI 456906) is a dual GLP-1 and glucagon receptor agonist developed by Boehringer Ingelheim and Zealand Pharma. Unlike tirzepatide (which pairs GLP-1 with GIP), survodutide pairs GLP-1 with glucagon — prioritizing energy expenditure over insulin sensitization.

Trial Data

Phase 2 results published in The New England Journal of Medicine (Blüher et al., 2024):

• Highest dose (4.8 mg): 18.7% body weight loss at 46 weeks
• Separate Phase 2 trial in MASH (metabolic dysfunction-associated steatohepatitis) showed significant reductions in liver fat
• Phase 3 trials (the SYNCHRONIZE program) are currently underway

Mechanism Advantage

Survodutide’s GLP-1/glucagon combination offers advantages in fat oxidation that GIP-based dual agonists may not provide. The glucagon component drives lipolysis and hepatic fat mobilization — which is why survodutide has shown promising liver fat data. For researchers interested in metabolic effects beyond weight loss, particularly hepatic steatosis, survodutide’s profile is distinct.

Available for research: Survodutide

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5. Mazdutide — The Dual Agonist From China

What It Is

Mazdutide (LY3305677/IBI362) is a dual GLP-1 and glucagon receptor agonist developed by Innovent Biologics in partnership with Eli Lilly. It shares the GLP-1/glucagon mechanism with survodutide but represents a different molecular design. Mazdutide was approved in China for type 2 diabetes in July 2024.

Trial Data

Phase 2 results published in The Lancet Diabetes & Endocrinology (2024):

• 9 mg dose: approximately 14.4% body weight loss at 48 weeks in Chinese adults with obesity
• Phase 3 trials (the GLORY program) are underway for the obesity indication
• Already approved in China for type 2 diabetes, signaling regulatory momentum

Mechanism Advantage

Mazdutide’s approval in China for diabetes provides clinical validation of the GLP-1/glucagon dual mechanism in a regulatory setting. While its weight loss numbers are lower than survodutide’s at this stage, Phase 3 data may narrow or close that gap. The compound represents the growing global interest in multi-receptor agonists beyond the US and European markets.

Available for research: Mazdutide

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Head-to-Head Comparison: What the Trial Data Shows

Compound	Receptors Targeted	Mechanism Type	Best Trial Result	Phase	Journal	Year
Retatrutide	GIP + GLP-1 + Glucagon	Triple agonist	24.2% body weight loss	Phase 2	NEJM	2023
Tirzepatide	GIP + GLP-1	Dual agonist	20.9% body weight loss	Phase 3	NEJM	2022
Survodutide	GLP-1 + Glucagon	Dual agonist	18.7% body weight loss	Phase 2	NEJM	2024
Semaglutide	GLP-1	Single agonist	14.9% body weight loss	Phase 3	NEJM	2021
Mazdutide	GLP-1 + Glucagon	Dual agonist	14.4% body weight loss	Phase 2	Lancet D&E	2024

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Single vs Dual vs Triple: What the Data Shows

The progression from single to dual to triple agonism tells a clear story in the clinical data: each additional receptor target has produced larger weight loss numbers in clinical trials.

Single → Dual: Semaglutide’s 14.9% (GLP-1 alone) was surpassed by tirzepatide’s 20.9% (GLP-1 + GIP). Adding the GIP receptor produced roughly 40% greater weight reduction. The mechanism: GIP enhances insulin sensitivity and glucose metabolism through pathways that GLP-1 does not fully engage.

Dual → Triple: Retatrutide’s 24.2% (GLP-1 + GIP + Glucagon) surpassed tirzepatide’s 20.9%. Adding glucagon receptor activation produced an additional ~16% improvement. The mechanism: glucagon increases energy expenditure and fat oxidation, adding a thermogenic component that dual agonists lack.

The glucagon question: Two different dual-agonist approaches are being tested — GLP-1/GIP (tirzepatide) and GLP-1/glucagon (survodutide, mazdutide). Survodutide’s 18.7% suggests that the GLP-1/glucagon combination alone may produce results comparable to GLP-1/GIP, but through a different mechanism (energy expenditure vs insulin sensitization). Retatrutide captures both by targeting all three receptors.

Important caveats: These comparisons are indirect — they come from separate trials with different populations, durations, and designs. No head-to-head trial comparing these compounds has been published. Additionally, retatrutide and survodutide are still in Phase 2, while semaglutide and tirzepatide have Phase 3 data with much larger sample sizes. Phase 3 results frequently differ from Phase 2.

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What This Means for Research

The multi-receptor agonist field is moving fast. Semaglutide established the benchmark. Tirzepatide proved that dual targeting improves outcomes. Retatrutide suggests that triple targeting may improve them further. Survodutide and mazdutide demonstrate that the specific receptor combination matters — not just the number of receptors targeted.

The key question for the next phase of research is whether the Phase 2 results for retatrutide, survodutide, and mazdutide will hold up in the larger, longer Phase 3 trials currently underway. If retatrutide’s 24.2% translates to Phase 3, it would represent the most effective anti-obesity compound ever brought to late-stage clinical development.

All compounds discussed in this article are the subject of ongoing research and clinical trials. Published trial data represents specific study populations and controlled conditions. Individual research applications should be designed with appropriate protocols and oversight.

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Frequently Asked Questions

Which GLP-1 agonist showed the highest weight loss in clinical trials?

Retatrutide demonstrated the highest mean body weight reduction at 24.2% in a Phase 2 trial published in The New England Journal of Medicine (2023). However, this is Phase 2 data from 338 participants. Tirzepatide holds the highest Phase 3 result at 20.9% from over 2,500 participants. Phase 3 data for retatrutide is still pending from the TRIUMPH program.

What is the difference between a single, dual, and triple agonist?

These terms refer to how many receptor types the compound activates. Semaglutide is a single agonist (GLP-1 only). Tirzepatide is a dual agonist (GIP + GLP-1). Retatrutide is a triple agonist (GIP + GLP-1 + Glucagon). Each additional receptor target engages a different metabolic pathway — adding GIP enhances insulin sensitivity, while adding glucagon increases energy expenditure and fat oxidation.

Are retatrutide, survodutide, and mazdutide FDA-approved?

No. Retatrutide is in Phase 3 trials (TRIUMPH program). Survodutide is in Phase 3 trials (SYNCHRONIZE program). Mazdutide is approved in China for type 2 diabetes but is not FDA-approved and is still in Phase 3 trials (GLORY program) for obesity. Only semaglutide (as Wegovy) and tirzepatide (as Zepbound) are FDA-approved for chronic weight management.

How do GLP-1/glucagon dual agonists differ from GLP-1/GIP dual agonists?

GLP-1/GIP dual agonists like tirzepatide enhance insulin sensitivity and glucose metabolism through the GIP receptor, which is primarily expressed in the gut, pancreas, and adipose tissue. GLP-1/glucagon dual agonists like survodutide increase energy expenditure and promote fat oxidation through the glucagon receptor, primarily expressed in the liver. The glucagon component drives the body to burn more energy, while the GIP component improves how the body processes glucose. These are mechanistically distinct approaches that may be complementary — which is why retatrutide targets all three.