Glucagon Receptor Agonists for Weight Loss: The Triple Agonist Approach
Written by Adam Maggio | Medically reviewed by Dr. Sarah Chen, PharmD, BCPS
Triple agonists like retatrutide incorporate glucagon to increase energy expenditure, achieving weight loss comparable to bariatric surgery.
The success of GLP-1 and GIP receptor agonists in obesity management has paved the way for even more sophisticated multi-agonist approaches. Among these, the inclusion of glucagon receptor agonism, particularly in triple agonists like retatrutide, represents a significant leap forward, offering a unique mechanism to enhance energy expenditure and achieve unprecedented weight loss.
The Multifaceted Role of Glucagon
Traditionally, glucagon is known for its role in raising blood glucose levels by stimulating hepatic glucose production. However, glucagon receptors are also expressed in various other tissues, including adipose tissue, the brain, and the heart, where they exert diverse metabolic effects. Recent research has highlighted glucagon's potential in weight management through mechanisms distinct from its glucose-raising effects:
Increased Energy Expenditure: Glucagon agonism can stimulate thermogenesis, particularly in brown adipose tissue, leading to increased energy expenditure and calorie burning [1]. This effect is crucial for promoting a negative energy balance, which is essential for weight loss.
Appetite Suppression: While not as potent as GLP-1, glucagon can also contribute to satiety and reduce food intake through central mechanisms [2].
Lipid Metabolism: Glucagon has been shown to promote lipolysis (fat breakdown) and reduce hepatic steatosis (fatty liver), contributing to improved metabolic health.
Retatrutide: The Triple Agonist Pioneer
Retatrutide (Eli Lilly) is a groundbreaking investigational drug that acts as a triple agonist, simultaneously activating GLP-1, GIP, and glucagon receptors. This innovative design aims to harness the synergistic benefits of all three incretin pathways to achieve superior weight loss and metabolic improvements.
Synergistic Mechanisms of Action
GLP-1 Agonism: Provides potent appetite suppression, slows gastric emptying, and enhances glucose-dependent insulin secretion.
GIP Agonism: Contributes to appetite suppression, improves insulin sensitivity, and promotes healthy adipose tissue function.
Glucagon Agonism: Uniquely enhances energy expenditure through thermogenesis, further promoting fat loss and complementing the appetite-suppressing effects of GLP-1 and GIP.
The combination of these three mechanisms creates a powerful anti-obesity effect that targets multiple facets of energy balance and metabolic regulation.
Clinical Efficacy of Retatrutide
The phase II clinical trial results for retatrutide have been remarkably impressive, setting new benchmarks for pharmacologically induced weight loss. In a 48-week study involving individuals with obesity or overweight, retatrutide demonstrated dose-dependent weight reductions:
Participants receiving the highest dose (12 mg once weekly) achieved an average body weight reduction of 24.2% [3]. This level of weight loss is comparable to, and in some cases exceeds, that achieved with bariatric surgery, which is currently considered the most effective treatment for severe obesity.
A significant proportion of participants achieved substantial weight loss, with over 60% losing at least 20% of their body weight, and nearly 30% losing 25% or more [3].
Beyond weight loss, retatrutide also led to significant improvements in various cardiometabolic parameters, including blood pressure, lipid profiles, and glycemic control.
Addressing Concerns: Glucagon's Hyperglycemic Effect
Historically, concerns about glucagon receptor agonism have revolved around its potential to increase blood glucose levels. However, in the context of a triple agonist like retatrutide, the potent GLP-1 and GIP agonism effectively counteracts this effect. The glucose-lowering actions of GLP-1 and GIP, coupled with the overall weight loss, lead to a net improvement in glycemic control, even in individuals with type 2 diabetes [4]. This demonstrates the careful balance and synergistic design of multi-agonist therapies.
Conclusion
The triple agonist approach, exemplified by retatrutide, represents a groundbreaking advancement in obesity medicine. By strategically combining GLP-1, GIP, and glucagon receptor agonism, these therapies offer a comprehensive solution that not only suppresses appetite but also significantly boosts energy expenditure. The unprecedented weight loss observed with retatrutide signals a new era in the pharmacological treatment of obesity, offering hope for millions struggling with this chronic disease and potentially transforming clinical practice.
References
[1] Finan, B., et al. (2025). A once-daily GLP-1/GIP/glucagon receptor tri-agonist... ScienceDirect. https://www.sciencedirect.com/science/article/pii/S2212877825000365
[2] Jastreboff, A. M., et al. (2023). Triple–Hormone-Receptor Agonist Retatrutide for Obesity. New England Journal of Medicine. https://www.nejm.org/doi/full/10.1056/NEJMoa2301972
[3] Eli Lilly and Company. (2023, June 22). Lilly's investigational tirzepatide shows up to 24.2% weight loss in adults with obesity or overweight in Phase 2 trial. Press Release. https://investor.lilly.com/news-releases/news-release-details/lillys-investigational-tirzepatide-shows-242-weight-loss-adults
[4] Melson, E., Ashraf, U., Papamargaritis, D., & Davies, M. J. (2025). What is the pipeline for future medications for obesity? International Journal of Obesity, 49*, 433–451. https://www.nature.com/articles/s41366-024-01473-y