GLP-1 and the Future of Obesity Medicine: Beyond Tirzepatide

Written by Adam Maggio | Medically reviewed by Dr. Sarah Chen, PharmD, BCPS

Explore the future of obesity medicine beyond tirzepatide, focusing on oral GLP-1 agonists and multi-receptor therapies like retatrutide.

The landscape of obesity pharmacotherapy is rapidly evolving, with glucagon-like peptide-1 (GLP-1) receptor agonists having revolutionized weight management. While semaglutide (Wegovy, Ozempic) and tirzepatide (Zepbound, Mounjaro) currently dominate the market, a robust pipeline of novel agents promises even greater efficacy and broader accessibility.

Oral GLP-1 Agonists: Enhancing Accessibility

Injectable GLP-1 receptor agonists have demonstrated significant weight loss, but the need for subcutaneous administration can be a barrier for some patients. Oral formulations are emerging as a key development to improve convenience and adherence. Oral semaglutide (Rybelsus), initially approved for type 2 diabetes, has shown promise for weight loss. A 68-week phase 3 trial (OASIS-1) of oral semaglutide 50 mg once daily resulted in a 17.4% mean weight loss compared to 1.8% with placebo in individuals with obesity without type 2 diabetes [1]. This represents a substantial improvement over the 4.4 kg weight loss seen with the 14 mg dose in type 2 diabetes patients [1].

Another significant oral contender is orforglipron (Eli Lilly), a non-peptide GLP-1 receptor agonist. Phase II trial data revealed that orforglipron led to significant weight reductions, with participants on a 36 mg dose achieving an average of 11.2% body weight loss over 72 weeks, compared to 2.1% with placebo [2]. While these figures are slightly lower than the highest doses of injectable semaglutide or tirzepatide, the oral route of administration offers a compelling advantage for patient preference and broader adoption.

Multi-Agonists: Targeting Multiple Pathways for Enhanced Efficacy

The success of tirzepatide, a dual GLP-1 and glucose-dependent insulinotropic polypeptide (GIP) receptor agonist, has paved the way for multi-agonist therapies that target multiple entero-pancreatic hormone pathways. These agents aim to leverage synergistic effects to achieve even greater weight loss and metabolic benefits.

Retatrutide (Eli Lilly) stands out as a triple agonist, activating GLP-1, GIP, and glucagon receptors. Early phase II trial data for retatrutide have been particularly impressive, demonstrating up to a 24.2% reduction in body weight after 48 weeks at the highest dose (12 mg) [2]. This level of weight loss approaches that achieved with bariatric surgery, marking a potential paradigm shift in obesity treatment. The glucagon receptor agonism component is hypothesized to contribute to increased energy expenditure, complementing the appetite-suppressing effects of GLP-1 and GIP.

Cagrilintide-semaglutide (CagriSema) is another promising combination therapy under investigation by Novo Nordisk. This co-formulation combines semaglutide (a GLP-1 receptor agonist) with cagrilintide, a long-acting amylin analog. Amylin, a hormone co-secreted with insulin, plays a role in satiety and gastric emptying. The combination aims to provide enhanced weight loss through complementary mechanisms. Phase III trials are underway, with early data suggesting significant weight reductions.

Beyond Incretins: Novel Mechanisms of Action

While incretin-based therapies dominate the current pipeline, other novel mechanisms are also being explored:

Oxyntomodulin (OXM) analogs: OXM is a naturally occurring gut hormone that acts as a dual GLP-1 and glucagon receptor agonist. Analogs of OXM are being developed to harness its potential for weight loss through both appetite suppression and increased energy expenditure. Pre-clinical and early clinical studies have shown promising results in reducing body weight.

FGF21 analogs: Fibroblast Growth Factor 21 (FGF21) is a hormone involved in metabolic regulation, including glucose and lipid metabolism. FGF21 analogs are being investigated for their potential to improve metabolic health and induce weight loss, particularly in conditions like non-alcoholic steatohepatitis (NASH).

Leptin sensitizers: Leptin is a hormone that signals satiety to the brain. In many individuals with obesity, leptin resistance develops, meaning the brain no longer responds effectively to leptin's signals. Leptin sensitizers aim to restore the brain's responsiveness to leptin, thereby promoting weight loss. This approach addresses a fundamental aspect of obesity pathophysiology.

Melanocortin-4 Receptor (MC4R) agonists: The MC4R pathway in the hypothalamus plays a crucial role in regulating hunger and energy expenditure. Setmelanotide, an MC4R agonist, is approved for specific genetic forms of obesity caused by deficiencies in the MC4R pathway. Further research into MC4R agonists may lead to broader applications in obesity management.

The Evolving Landscape

The future of obesity medicine is moving towards more potent, multi-targeted therapies and more convenient oral formulations. These advancements offer hope for individuals struggling with obesity, providing a wider array of effective treatment options that can be tailored to individual patient needs and preferences. The ongoing research and development in this field underscore a deeper understanding of the complex pathophysiology of obesity and the commitment to addressing this global health challenge.

References

[1] 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

[2] Robertson, J. (2025, October 3). Beyond GLP-1: the next wave of weight-loss medication innovation. The Pharmaceutical Journal. https://pharmaceutical-journal.com/article/feature/beyond-glp-1-the-next-wave-of-weight-loss-medication-innovation