History of GLP-1 Drugs: Gila Monster Venom to Blockbuster
GLP-1 Drug Classes
120 years
From the first observation that gut extracts lower blood glucose in 1906 to today's multi-billion-dollar GLP-1 market, the incretin story spans over a century of science.
Rehfeld, Frontiers in Endocrinology, 2018
Rehfeld, Frontiers in Endocrinology, 2018
View as imageThe most prescribed weight loss drugs in the world trace their origin to a venomous lizard found in the deserts of the American Southwest. That is not a marketing story. It is a direct line from basic venom research in the late 1980s to a drug class that generated over $50 billion in revenue in 2024. The history of GLP-1 drugs is also the history of how a short-acting peptide with a two-minute half-life was engineered into once-weekly injections that produce 15 to 24% body weight loss.
Every GLP-1 receptor agonist on the market today exists because researchers connected three separate threads: a century-old observation about gut hormones, a peptide in lizard venom that mimics one of those hormones, and lipid engineering that extended its duration from minutes to days.
Key Takeaways
- The incretin concept dates to 1906, when researchers first showed that gut extracts could lower blood glucose[1]
- GLP-1 was identified in 1986 by Habener and Mojsov, but its two-minute half-life made direct therapeutic use impossible[2]
- Exendin-4, a 39-amino-acid peptide from Gila monster venom, was discovered in 1992 and became the template for the first GLP-1 drug[3]
- Exenatide (Byetta) was FDA-approved in 2005 as the first GLP-1 receptor agonist, followed by liraglutide (2010), semaglutide (2017), and tirzepatide (2022)[4]
- Fatty acid conjugation to the peptide backbone was the key engineering advance that transformed twice-daily injections into once-weekly treatments[5]
- Machine learning is now being used to design next-generation GLP-1 agonists with improved pharmacological properties[6]
The Incretin Concept: 1906 to 1986
The story begins over a century before the first GLP-1 drug reached patients. In 1906, a group of researchers in Liverpool demonstrated that an extract from the intestinal mucosa could lower blood glucose when administered to animals. They had discovered, without knowing it, the incretin effect: the observation that oral glucose stimulates more insulin release than the same amount of glucose given intravenously.[1]
Rehfeld (2018) traced the full history of the incretin concept in Frontiers in Endocrinology. Interest in gut-derived insulin-stimulating factors waned after the discovery of insulin in 1921, which seemed to explain glucose regulation entirely. It was not until the 1960s that researchers definitively proved the gastrointestinal tract releases important insulinotropic factors upon oral glucose intake.[1]
The first incretin hormone identified was glucose-dependent insulinotropic polypeptide (GIP), isolated in 1970. But GIP had a critical limitation: it does not stimulate insulin secretion in patients with type 2 diabetes. This meant GIP could not serve as a therapeutic target for the disease it was most needed for.[7]
The breakthrough came in 1983 when Joel Habener and colleagues sequenced the proglucagon gene and found evidence for a second, glucagon-related peptide. In 1986, Habener and Svetlana Mojsov identified GLP-1(7-37) in the intestine as a cleavage product of proglucagon. Early in 1987, Mojsov, Weir, and Habener tested its insulinotropic effect and found it potently stimulated insulin secretion six-fold at physiologic concentrations.[2]
Unlike GIP, GLP-1's action was preserved in patients with type 2 diabetes. This made it immediately interesting as a therapeutic target. There was one problem: native GLP-1 has a half-life of approximately two minutes in the human bloodstream. The enzyme dipeptidyl peptidase-4 (DPP-4) degrades it almost immediately after secretion. A drug that works for two minutes is not a drug.
The Gila Monster Connection: 1992
The solution came from an unexpected source. Dr. John Eng, an endocrinologist at the Veterans Administration Medical Center in the Bronx, New York, had been studying bioactive peptides in animal venoms. He was interested in the Gila monster (Heloderma suspectum) because the lizard can survive long periods without eating while maintaining stable blood glucose.
Eng assayed Gila monster venom and discovered a 39-amino-acid peptide he named exendin-4. It shared roughly 53% sequence identity with human GLP-1 and activated the same receptor, but with a critical difference: exendin-4 resisted degradation by DPP-4. Where native GLP-1 lasted minutes, exendin-4 remained active for hours.[3]
Yap and Misuan (2019) reviewed the full trajectory from discovery to clinical application in Basic & Clinical Pharmacology & Toxicology. Eng published his findings in 1992. He and colleague John Raufman convinced a small startup called Amylin Pharmaceuticals to develop a synthetic version. Amylin quickly showed that synthetic exendin-4 normalized blood glucose in type 2 diabetic mice. Human trials followed.[3]
Kondo et al. (2025) analyzed how single amino acid substitutions in the exendin-4 sequence affect GLP-1 receptor agonist activity, demonstrating that the original venom peptide remains a template for ongoing drug design nearly three decades after its discovery.[8]
First Generation: Exenatide (2005)
Synthetic exendin-4, renamed exenatide, received FDA approval in April 2005 under the brand name Byetta. It was the first GLP-1 receptor agonist to reach patients. The drug required twice-daily injections and produced modest weight loss (2 to 3 kg) alongside glycemic improvements.
Buse et al. (2010) published the DURATION-1 trial results in Diabetes Care, showing that a once-weekly extended-release formulation of exenatide (Bydureon) produced sustained glycemic control and weight loss over 52 weeks. This demonstrated that the exendin-4 backbone could be formulated for less frequent dosing, though the mechanism (microsphere encapsulation) was different from what later drugs would use.[4]
Exenatide proved the concept: a peptide derived from lizard venom could safely and effectively treat type 2 diabetes in humans. But the twice-daily injection schedule and relatively modest efficacy left room for improvement.
Second Generation: Liraglutide (2010)
Novo Nordisk took a different approach. Rather than using the exendin-4 backbone, they modified human GLP-1 itself. Liraglutide is a GLP-1 analog with 97% sequence homology to native human GLP-1, modified with a C16 fatty acid (palmitic acid) attached via a glutamic acid spacer to lysine at position 26.
The fatty acid addition was the key innovation. It allowed liraglutide to bind reversibly to albumin in the bloodstream, protecting it from DPP-4 degradation and slowing renal clearance. This extended the half-life from two minutes to approximately 13 hours, enabling once-daily dosing.
Liraglutide received FDA approval as Victoza for type 2 diabetes in 2010. Weight loss was more substantial than with exenatide, typically around 5 to 8% of body weight. In 2014, a higher-dose formulation (3.0 mg) was approved as Saxenda, becoming the first GLP-1 receptor agonist specifically approved for chronic weight management.
Seino et al. (2010) compared the two incretin hormones GIP and GLP-1, noting their similarities and differences in receptor signaling, which laid groundwork for the dual-agonist approach that would come later with tirzepatide.[7]
Third Generation: Semaglutide (2017)
Semaglutide represented a further leap in peptide engineering. Novo Nordisk modified the GLP-1 backbone with two amino acid substitutions (Aib at position 8 to resist DPP-4, and Arg at position 34) and attached a C18 fatty diacid chain via a linker at position 26. The C18 fatty acid provided stronger albumin binding than liraglutide's C16, extending the half-life to approximately 7 days.
This chemistry enabled once-weekly dosing. Semaglutide was approved as Ozempic for type 2 diabetes in December 2017.
Shi et al. (2018) published a systematic review and meta-analysis of once-weekly semaglutide for type 2 diabetes in Frontiers in Pharmacology, confirming its efficacy and safety profile across the SUSTAIN clinical trial program.[5]
Husain et al. (2020) analyzed data from the SUSTAIN and PIONEER trial programs, demonstrating that semaglutide reduced cardiovascular events in type 2 diabetes patients across varying cardiovascular risk profiles.[9]
The weight loss efficacy was striking. The STEP clinical trials showed that higher-dose semaglutide (2.4 mg weekly) produced approximately 15% body weight loss, far exceeding any previous pharmaceutical intervention. Semaglutide at this dose was approved as Wegovy for chronic weight management in June 2021.
In 2024, semaglutide (Wegovy) became the first weight loss drug also approved for reducing the risk of serious cardiovascular events, based on the SELECT trial.
Fourth Generation: Tirzepatide and Multi-Agonism (2022)
Eli Lilly's tirzepatide introduced a new concept: dual incretin agonism. Rather than targeting only the GLP-1 receptor, tirzepatide activates both the GLP-1 receptor and the GIP receptor. This was a return to the GIP story, but with a twist. While GIP alone does not stimulate insulin secretion in type 2 diabetes, combining GIP and GLP-1 receptor activation produced additive and potentially synergistic effects on glucose control and weight loss.
Min and Bain (2021) reviewed the role of tirzepatide as a dual GIP and GLP-1 receptor agonist, published in Diabetes Therapy.[10]
Tirzepatide is a 39-amino-acid peptide based on the GIP sequence but engineered with GLP-1 receptor cross-reactivity and a C20 fatty diacid that provides once-weekly pharmacokinetics. It was approved as Mounjaro for type 2 diabetes in May 2022 and as Zepbound for chronic weight management in November 2023.
The SURMOUNT-1 trial demonstrated approximately 22.5% body weight loss at the highest dose (15 mg weekly), the largest weight reduction achieved by any pharmaceutical agent. In late 2024, tirzepatide became the first GLP-1-class drug approved for obstructive sleep apnea.
What Comes Next
The pipeline extends the multi-agonist approach further. Retatrutide, a triple agonist targeting GLP-1, GIP, and glucagon receptors simultaneously, produced approximately 24% weight loss in Phase 2 trials. Survodutide, pemvidutide, and others target different receptor combinations.
Beyond biology, the drug design process itself is changing. Nielsen et al. (2024) published in the Journal of Medicinal Chemistry on machine-learning-guided peptide drug discovery, demonstrating that computational approaches could identify GLP-1 receptor agonists with improved pharmacological properties compared to traditional medicinal chemistry approaches.[6]
Motokura et al. (2026) showed in The Journal of Endocrinology that the incretin effect alone is sufficient for glucose control in developing rats, a finding that reinforces the fundamental importance of the incretin system and suggests even more therapeutic applications may emerge.[11]
The trajectory is clear: from a gut extract that lowered glucose in 1906, to a lizard peptide in 1992, to a class of drugs that every GLP-1 receptor agonist article now needs a comparison table to cover. Each generation solved a specific pharmacological problem (DPP-4 resistance, half-life extension, receptor selectivity) and each opened the door to broader indications.
The 2024 Lasker~DeBakey Clinical Medical Research Award, one of the highest honors in medical science, went to Joel Habener and Svetlana Mojsov for their discovery of GLP-1(7-37) and to Lotte Bjerre Knudsen for developing the sustained-acting versions that became liraglutide and then semaglutide. The award recognized a line of research that took nearly four decades to move from basic discovery to global therapeutic impact.
The Bottom Line
The GLP-1 drug class spans over a century of scientific discovery. The incretin concept was first observed in 1906, GLP-1 was identified in 1986, and exendin-4 from Gila monster venom provided the DPP-4-resistant template that made therapeutic development possible. Six GLP-1 receptor agonists have reached the market since 2005, with each generation solving a specific pharmacological limitation. Weight loss efficacy has increased from 2-3% with exenatide to over 22% with tirzepatide, and indications have expanded from diabetes to obesity, cardiovascular risk reduction, and sleep apnea. The field continues to evolve through multi-agonist approaches and machine-learning-guided drug design.