From Gila monster venom to global blockbuster — the extraordinary 40-year story of a hormonal revolution in medicine
GLP-1 receptor agonists began as a curiosity in endocrinology labs and became among the most transformative drug class of the 21st century — reshaping how medicine approaches type 2 diabetes, obesity, cardiovascular disease, and beyond. This is their story.
Year GLP-1 was first identified
Approved GLP-1 RA drugs globally
Body weight reduction with semaglutide
Projected annual market by 2030
Glucagon-like peptide-1 is secreted from L-cells in the gut after food intake. It stimulates insulin and suppresses glucagon — but has a half-life of only ~2 minutes.
GLP-1 RAs are engineered analogues that bind GLP-1 receptors on pancreatic beta cells, slowing gastric emptying, reducing appetite, and promoting glucose-dependent insulin secretion.
GLP-1 receptors are found in the heart, brain, kidneys, and liver — explaining the cardiovascular, renal, and neuroprotective benefits seen in landmark trials.
Acting on hypothalamic and brainstem receptors, GLP-1 RAs reduce hunger and food cravings — the key mechanism behind profound weight loss effects.
Unlike native GLP-1 (degraded rapidly by DPP-4 enzymes), pharmacological analogues are engineered with structural modifications to extend plasma half-life from minutes to days or even a week.
Insulin stimulation only occurs when blood glucose is elevated — minimising hypoglycaemia risk and offering a significant safety advantage over older antidiabetic agents.
Researchers Graeme Bell, Daniel Drucker, and colleagues cloned the proglucagon gene. GLP-1 was identified as a potent insulinotropic hormone secreted by intestinal L-cells, laying the foundation for the entire drug class.
Drucker and colleagues demonstrated GLP-1's glucose-lowering action in human subjects. Michael Nauck's landmark studies in 1993 showed that GLP-1 infusion dramatically normalised blood sugar in type 2 diabetics — but the 2-minute half-life made native GLP-1 impractical as a drug.
Endocrinologist John Eng at the VA Medical Center discovered Exendin-4, a peptide in the saliva of the Gila monster lizard with 53% homology to human GLP-1 — but resistant to DPP-4 degradation. The molecule had a half-life of hours rather than minutes. This became the basis for exenatide.
Novo Nordisk scientists, led by Lotte Bjerre Knudsen, began developing a human GLP-1 analogue. By attaching a C-16 fatty acid chain, they created a molecule that bound albumin in blood — extending half-life to ~13 hours and enabling once-daily dosing.
Amylin Pharmaceuticals and Eli Lilly received FDA approval for exenatide (Byetta), the first GLP-1 receptor agonist for type 2 diabetes. Given as a twice-daily injection, it showed HbA1c reductions of ~1% and meaningful weight loss — validating the entire concept.
Novo Nordisk's once-daily liraglutide (Victoza) received FDA approval. With superior HbA1c reduction vs exenatide and more substantial weight loss (~3 kg average), it rapidly gained market share and became the dominant GLP-1 RA of the 2010s.
AstraZeneca and Amylin received approval for exenatide extended-release (Bydureon) — the first once-weekly GLP-1 RA. Albiglutide and dulaglutide followed, expanding the once-weekly market. Patient adherence improved dramatically with reduced injection frequency.
The LEADER trial demonstrated that liraglutide significantly reduced major adverse cardiovascular events (MACE) in high-risk patients with T2D — a first for an antidiabetic drug. This transformed GLP-1 RAs from glucose-lowering agents to cardioprotective medicines, reshaping guidelines globally.
Novo Nordisk's once-weekly semaglutide (Ozempic) was approved for T2D. Structurally modified with two amino acid substitutions and a C-18 fatty di-acid chain, it achieved ~50x higher albumin binding than liraglutide and a true 7-day half-life — enabling once-weekly dosing with superior efficacy.
The SUSTAIN-6 trial confirmed semaglutide's cardiovascular benefits. Simultaneously, Novo Nordisk developed an oral formulation using the SNAC absorption enhancer technology. Rybelsus (oral semaglutide) was approved in 2019 — the world's first oral GLP-1 RA, eliminating the injection barrier.
High-dose semaglutide 2.4 mg (Wegovy) received FDA approval for chronic weight management — the first anti-obesity drug approved in nearly a decade. The STEP trials showed ~15% average body weight reduction; some participants lost over 20%. Demand immediately overwhelmed supply globally.
Eli Lilly's tirzepatide (Mounjaro) was approved for T2D, then Zepbound for obesity in 2023. A dual GIP/GLP-1 receptor agonist, it achieved unprecedented ~22.5% body weight loss in SURMOUNT trials — surpassing all prior pharmacological weight loss benchmarks and approaching bariatric surgery outcomes.
The SELECT trial showed semaglutide reduced cardiovascular events in obese/overweight patients without diabetes — broadening indications beyond T2D. The FDA approved semaglutide for reducing cardiovascular risk in obesity (2024). Trials for CKD, NASH, sleep apnoea, and Parkinson's disease are ongoing.
Retatrutide (GIP/GLP-1/glucagon triple agonist) and orforglipron (oral non-peptide GLP-1 RA) are in late-stage trials. Oral tirzepatide is in development. Daily injections may soon give way to oral once-weekly pills — democratising access to the drug class and potentially defining the next era.
The pioneer. Based on Gila monster exendin-4, the first approved GLP-1 RA validated the entire therapeutic concept. Now largely superseded but historically pivotal.
The first human GLP-1 analogue. Dominated the market throughout the 2010s with superior tolerability, cardiovascular data (LEADER), and the first anti-obesity approval (Saxenda, 2014) in the class.
A GLP-1/Fc fusion protein that allowed once-weekly dosing with an autoinjector pen. REWIND trial confirmed CV benefit; notable for CV benefit in patients with lower CV risk at baseline.
Transformed the class. Unprecedented HbA1c reductions (~1.5–1.8%), robust weight loss, and SUSTAIN-6 CV data. Became a cultural phenomenon as off-label weight loss soared, fuelling global shortages.
A breakthrough in formulation science. SNAC absorption enhancer enables intestinal absorption of a peptide that was thought impossible to deliver orally. Removes the injection barrier for needle-averse patients.
The obesity landmark. STEP trials showed ~15% average weight loss — 2x prior pharmacological benchmarks. SELECT (2023) extended CV benefit indication beyond T2D. Fundamentally changed obesity medicine.
First dual GIP + GLP-1 receptor agonist. SURPASS trials showed ~2.5% HbA1c reduction. Approved as Zepbound (2023) for obesity with ~22.5% weight loss in SURMOUNT — the highest weight loss ever seen pharmacologically.
FDA approved semaglutide to reduce the risk of serious CV events in adults with CVD plus overweight/obesity — independent of diabetes status. SELECT trial landmark: 20% relative risk reduction in MACE.
Retatrutide (GIP + GLP-1 + glucagon) showed ~24% weight loss in Phase 2 trials — entering Phase 3. Cagrilintide combinations with semaglutide (CagriSema) show additive effects.
Orforglipron (Eli Lilly) and danuglipron — small molecule oral GLP-1 RAs with no absorption-enhancer requirement — could revolutionise accessibility and cost of the drug class.
Trials are underway for GLP-1 RAs in Alzheimer's disease, Parkinson's disease, alcohol use disorder, and addiction. The brain's GLP-1 receptor distribution suggests broad potential beyond metabolic disease.
Semaglutide recently showed efficacy in metabolic dysfunction-associated steatohepatitis (MASH/NASH). GLP-1 RAs are emerging as kidney-protective agents in diabetic nephropathy and CKD.
Emerging data suggests GLP-1 RAs may reduce risk of obesity-related cancers. Mechanistic studies on GLP-1 receptor expression in tumour microenvironments are early but intriguing.
With semaglutide patents expiring ~2026 in some jurisdictions, biosimilar and generic competition could dramatically lower prices — potentially making these medicines accessible to billions worldwide.