The obesity drug market is entering new phases, which includes Eli Lilly and Company advancing retatrutide, a next-generation “triple-G” therapy that could outperform its own marketed dual agonist Zepbound (tirzepatide).
While Zepbound is already a commercial success, retatrutide’s emerging clinical profile suggests it may raise the efficacy bar even further, though with potential trade-offs.
Related: Lilly’s Retatrutide Shows Promising A1C and Weight Reductions in First Diabetes Trial
Retatrutide vs. Zepbound: How Do They Compare?
Retatrutide differentiates itself mechanistically by targeting three hormones (GLP-1, GIP and glucagon), compared to Zepbound’s dual GLP-1/GIP activity. This added glucagon component is believed to enhance energy expenditure and fat metabolism, underpinning the drug’s more aggressive weight-loss profile.
Below is an overview of how the two compare:
Mechanism of Action:
Retatrutide: Triple agonist (GLP-1, GIP, glucagon)
Zepbound: Dual agonist (GLP-1, GIP)
Developer:
Retatrutide: Eli Lilly and Company (investigational)
Zepbound: Eli Lilly and Company (approved)
Regulatory Status:
Retatrutide: Phase III clinical development
Zepbound: FDA-approved for obesity, obstructive sleep apnea
Weight Loss Efficacy:
Retatrutide: Up to ~28.7% (68 weeks; no clear plateau)
Zepbound: ~20% to 22.5% (long-term studies)
Glycemic Control (T2D):
Retatrutide: HbA1c reduction up to ~2.0% (Phase III)
Zepbound: Strong, well-established HbA1c reductions (~2.0% to 2.4%) across Phase III trials
Durability of Effect:
Retatrutide: Sustained weight loss with continued decline over time
Zepbound: Durable, but tends to plateau earlier
Safety & Tolerability:
Retatrutide: Higher rates of GI side effects; more discontinuations observed
Zepbound: Better-established tolerability; more predictable safety profile
Commercial Status:
Retatrutide: Not yet marketed
Zepbound: Blockbuster franchise — part of the tirzepatide portfolio generating tens of billions in revenue
Clinical Positioning:
Retatrutide: Potential next-generation, high-efficacy option
Zepbound: Current standard among incretin-based obesity therapies
Strategic Role (Lilly Portfolio):
Retatrutide: Potential lifecycle successor to tirzepatide
Zepbound: Current market leader and revenue driver
Key Trade-Off:
Retatrutide: Higher efficacy vs. tolerability concerns
Zepbound: Slightly lower efficacy vs. stronger real-world usability
Retatrutide vs. Zepbound: The Details
Recent late-stage data have been fueling excitement around retatrutide. In the Phase III TRANSCEND-T2D-1 trial, the drug reduced HbA1c by up to 2.0% and delivered ~16.8% weight loss at 40 weeks, with no plateau observed.
Longer-duration studies suggest even greater potential: in a 68-week trial, patients lost up to 28.7% of body weight, exceeding outcomes typically seen with Zepbound. Earlier Phase II data also showed weight reductions approaching 24%.
In contrast, Zepbound has already demonstrated strong efficacy and safety across multiple Phase III programs, driving its rapid uptake in both diabetes and obesity.
Zepbound also has FDA approval for the treatment of moderate-to-severe obstructive sleep apnea (OSA) in adults with obesity, marking the first pharmacologic therapy indicated for this condition. The approval was supported by Phase III SURMOUNT-OSA data showing significant reductions in apnea-hypopnea index (AHI), alongside substantial weight loss. Zepbound is believed to improve OSA primarily through its weight-reducing effects, as weight loss can decrease upper airway obstruction and improve breathing during sleep.
By comparison, Zepbound has consistently delivered ~20% to 22.5% weight loss in long-term studies, placing it among the most effective approved therapies but still slightly below retatrutide’s upper range. In diabetes populations, tirzepatide remains highly competitive, with strong glycemic control and a more established tolerability profile.
That safety and tolerability profile may ultimately shape how the two drugs are positioned. While retatrutide’s efficacy is compelling, higher rates of gastrointestinal side effects and discontinuations have been observed in trials, raising questions about real-world adherence. Tirzepatide, on the other hand, benefits from a growing body of real-world evidence and clinician familiarity, which could sustain its dominance even as next-generation agents emerge.
The key question is whether retatrutide’s superior efficacy will outweigh tolerability concerns, and whether payers and physicians will embrace a step-change in outcomes at the potential cost of increased side effects.
What’s Next for the Obesity Drug Market?
Retatrutide will be released into an increasingly crowded and quickly evolving obesity landscape. Rival incretin-based therapies from Novo Nordisk, including semaglutide-based blockbusters Ozempic and Wegovy, continue to anchor the market, although Eli Lilly has been taking the edge with its tirzepatide products Mounjaro and Zepbound.
Meanwhile, next-generation candidates from companies such as Amgen and Structure Therapeutics are advancing through late-stage pipelines.
Amgen’s long-acting monthly obesity therapy MariTide (maridebart cafraglutide, formerly AMG 133) demonstrated substantial and sustained weight loss in a Phase II trial, with patients achieving an average of 20% weight loss without a plateau, along with cardiometabolic improvements, over 52 weeks. The treatment also showed a manageable safety profile, supporting its potential as a less-frequent dosing alternative to current GLP-1-based therapies.
Structure Therapeutics reported positive Phase II data for its oral GLP-1 receptor agonist aleniglipron, demonstrating dose-dependent weight loss of up to ~16% with no clear plateau and a tolerable safety profile.
The combined value of leading GLP-1 pipeline assets across Eli Lilly, Novo Nordisk and Amgen alone is estimated at roughly $68 billion.
At the same time, the competitive paradigm is shifting beyond injectables. Both Eli Lilly and Novo Nordisk are advancing oral GLP-1 therapies as well. This year, Novo Nordisk launched its oral Wegovy pill to kick start the year, while Eli Lilly followed with its own FDA approval for its oral GLP-1 Foundayo (orforglipron) in April.
Meanwhile, newer mechanisms, including muscle-preserving combinations and multi-agonist approaches, are being explored to differentiate future entrants and address limitations such as lean mass loss.
Analysts are increasingly viewing retatrutide not simply as a competitor to Zepbound, but as a potential successor within Eli Lilly’s own metabolic franchise. This internal lifecycle strategy could allow Eli Lilly to maintain its lead as the market expands, potentially exceeding $100 billion over the next decade, while fending off intensifying competition.
Zepbound achieved massive commercial success in 2025, with estimated full-year sales reaching approximately $13.5 billion, representing a near-tripling (+175%) of revenue compared to the prior year. Driven by high demand and increased production, Q4 2025 revenue alone hit $4.3 billion, serving as a key driver of Eli Lilly’s 2025 growth.
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