How GLP-1 Drugs Work: The Full Story, From Discovery to Your Prescription

Ozempic is now a household name. Wegovy is being discussed in cardiology clinics, diabetology practices, and morning television in the same breath. But most people — including many who are taking these medications — have only a vague understanding of what GLP-1 actually is, where it came from, or what it does inside the body.

That matters, because the mechanism is not just pharmacological trivia. Understanding how these drugs work helps patients use them more effectively and set more realistic expectations. It also explains why, despite all the noise, the underlying science is genuinely impressive.

What is GLP-1? The hormone that started everything.

GLP-1 stands for Glucagon-Like Peptide-1. It is a hormone produced naturally in the human body — specifically by the L-cells of the small intestine — in response to eating. When food enters the gut, GLP-1 is released into the bloodstream, where it performs several coordinated functions: it stimulates the pancreas to release insulin, suppresses the counter-regulatory hormone glucagon (which would otherwise raise blood sugar), slows the rate at which food moves from the stomach into the small intestine, and — crucially — acts on receptors in the brain to signal satiety.

It is, in essence, a meal-response hormone. Its natural half-life in the body is approximately two minutes. The enzyme DPP-4 breaks it down almost immediately, which is why the natural hormone cannot simply be given as a medication.

Where the science began

The story of GLP-1 starts in the early 1980s, and it involves some of the most rigorous basic science in modern endocrinology.

Danish physician and physiologist Jens Juul Holst, at the University of Copenhagen, is credited with discovering and describing GLP-1 — identifying it as an incretin hormone with important roles in glycaemic control. Simultaneously, at Harvard Medical School's Massachusetts General Hospital, Joel Francis Habener — working with his colleague Svetlana Mojsov — was doing foundational work on elucidating the role of incretin hormones including GLP-1. Mojsov synthesised a specific 31-amino acid fragment of GLP-1 and demonstrated, together with Gordon Weir at the Joslin Diabetes Center, that small quantities of lab-synthesised GLP-1 could trigger insulin release.

The third critical figure is Daniel Joshua Drucker, a Canadian endocrinologist at the University of Toronto, whose independent discoveries included the demonstration that proglucagon — the precursor molecule — could be cleaved into multiple glucagon-like peptides, including several distinct isoforms of GLP-1. Drucker's work established the biological actions of GLP-1 with enough clarity to make it a drug target.

All three — Holst, Habener, and Drucker — received the Warren Alpert Foundation Prize in 2020, the Canada Gairdner International Award in 2021, and the Princess of Asturias Award for Technical and Scientific Research in 2024 for this foundational work. These are among the most prestigious scientific recognitions in the world.

There is also the question of exenatide — the first GLP-1 receptor agonist approved for clinical use, in 2005. Its origin is unusual: it was derived from exendin-4, a peptide found in the saliva of the Gila monster lizard (Heloderma suspectum). The key insight was that exendin-4, unlike human GLP-1, was resistant to DPP-4 degradation — it lasted far longer in the body. Exenatide was the first drug in this class to be used in the treatment of Type 2 diabetes, receiving FDA approval in 2005. It proved the concept and opened the field.

The original intended use: Type 2 diabetes

The GLP-1 receptor agonist class was developed entirely for Type 2 diabetes management. The goal was straightforward: create a drug that mimics the action of GLP-1, lowers blood sugar after meals, and does not carry the hypoglycaemia risk of insulin or sulphonylureas (because GLP-1's insulin-stimulating effect is glucose-dependent — it works only when blood sugar is elevated, not at all times).

Weight loss was initially a side effect, not a primary objective. Clinical trial participants losing 5 to 8 percent of their body weight on liraglutide was an observation, not the reason the drug was developed.

Lotte Bjerre Knudsen, chief scientific advisor at Novo Nordisk, was instrumental in pushing the scientific question further — investigating whether GLP-1's effects in the brain could explain the weight loss, and whether higher doses could achieve clinically meaningful obesity treatment. It was Knudsen's team that studied liraglutide's path through mice and found it could access brain structures involved in appetite regulation, setting the foundation for the obesity indication.

From liraglutide to semaglutide: The engineering of a better molecule

The discovery of GLP-1's effects on glycaemic control and body weight regulation led to efforts to extend its half-life and make it therapeutically effective — first with short-acting, then with long-acting GLP-1 receptor agonists.

Novo Nordisk developed liraglutide, which entered clinical testing in 2000 as an injectable to treat diabetes. In 2010, it was approved by the FDA as Victoza to treat Type 2 diabetes. In 2014, it was approved as Saxenda for weight loss, achieving an average reduction of approximately 8 percent of overall body mass.

Then came semaglutide. Knudsen and a team of Novo Nordisk chemists led by Jesper Lau and Thomas Kruse set out to make a GLP-1 receptor agonist that could be administered once weekly. They tested thousands of different combinations of linkers, fatty acids, and amino acid sequence changes before arriving at semaglutide — an ultrastable receptor agonist in which a carboxylated fatty acid is coupled to the molecule via a hydrophilic linker, strengthening albumin binding and dramatically extending its half-life.

These engineering improvements extended the elimination half-life to approximately seven days — enabling the once-weekly dosing that became central to semaglutide's clinical advantage.

Semaglutide was approved for Type 2 diabetes in 2017 and for obesity in 2021, showing 17 to 18 percent weight loss in clinical trials — a magnitude of weight reduction previously seen only with bariatric surgery.

How it works in the body: The mechanism

GLP-1 receptor agonists work through several simultaneous pathways:

Pancreatic effects: They bind to GLP-1 receptors on pancreatic beta cells and stimulate insulin secretion — but only in response to elevated blood glucose. This glucose-dependence is what makes them far safer than older diabetes medications with respect to hypoglycaemia. They also suppress glucagon release from alpha cells, reducing hepatic glucose output.

Gastric effects: They slow gastric emptying — the rate at which food leaves the stomach and enters the small intestine. This blunts the postprandial glucose spike and, importantly, prolongs the sensation of fullness after eating.

Brain effects: This is the mechanism most relevant to weight loss. GLP-1 receptors are present in several brain regions including the hypothalamus, brainstem, and areas of the mesolimbic dopamine system. Activating these receptors reduces appetite, lowers the hedonic drive to eat (what is colloquially called "food noise"), and alters the perceived reward value of food. Patients on semaglutide frequently report that food simply becomes less compelling — not that they are white-knuckling their way through hunger, but that hunger itself has diminished.

Cardiovascular and metabolic effects: Beyond glucose and weight, GLP-1 receptor agonists have demonstrated direct cardioprotective effects. The LEADER trial enrolled 9,340 patients with Type 2 diabetes at high cardiovascular risk and demonstrated that liraglutide reduced major adverse cardiovascular events by 13 percent. The SUSTAIN-6 trial provided confirmatory evidence, showing a 26 percent reduction in MACE with semaglutide. These are not small effects — they represent a drug class that independently reduces the risk of heart attack, stroke, and cardiovascular death.

Brand names: Worldwide and in India

The GLP-1 receptor agonist class now includes several molecules, each with distinct brand identities:

Globally:

• Semaglutide (Novo Nordisk) — Ozempic (weekly injectable, diabetes), Wegovy (weekly injectable, obesity), Rybelsus (daily oral tablet, diabetes)

• Liraglutide (Novo Nordisk) — Victoza (daily injectable, diabetes), Saxenda (daily injectable, obesity)

• Dulaglutide (Eli Lilly) — Trulicity (weekly injectable, diabetes)

• Tirzepatide (Eli Lilly) — Mounjaro (diabetes), Zepbound (obesity); technically a dual GIP/GLP-1 agonist, the next evolution of this class

• Exenatide (AstraZeneca) — Byetta (twice daily), Bydureon (weekly)

In India (as of 2026):

The Indian market has expanded rapidly, driven by both the Novo Nordisk originator products and a growing ecosystem of domestic generics following patent expiry. DCGI-approved semaglutide brands in India currently include Ozempic (Novo Nordisk), Wegovy (Novo Nordisk), Extensior (co-marketed by Abbott), Poviztra (co-marketed by Emcure), and Rybelsus (oral, Novo Nordisk) from the originator side, as well as Indian generics including Sundae (Eris Lifesciences), Semasize (Alkem), Semaglyn (Zydus), Noveltreat, Obeda, and Semalix (Torrent, the only oral generic equivalent to Rybelsus).

In April 2026, Novo Nordisk cut Indian prices by approximately 48 percent, bringing Ozempic to approximately ₹5,660 per month and Wegovy's starter dose to the same level. Indian generic options start significantly lower — Eris Sundae at approximately ₹220 per shot, and Alkem Semasize from approximately ₹1,800 per month.

Liraglutide remains available in India as Victoza (diabetes) from Novo Nordisk. Dulaglutide is available as Trulicity (Eli Lilly). Tirzepatide (Mounjaro) has been approved in India and is available in select centres, though at significant cost.

What GLP-1 drugs do not do

They are not a cure for obesity. They treat the disease while they are being taken, in the same way an antihypertensive treats blood pressure. Stopping them, without robust lifestyle changes in place, typically results in weight regain over months.

They are not appropriate for everyone. Thyroid history, pancreatitis history, pregnancy, and several other factors constitute contraindications that require proper clinical assessment.

And they do not work in isolation. The clinical trials demonstrating their efficacy were all conducted alongside dietary modification and exercise. These are adjuncts to lifestyle change, not replacements for it.

The bigger picture

The development of GLP-1 receptor agonists represents one of the more significant advances in metabolic medicine in recent decades. What began as a basic science question about a short-lived gut hormone — studied in anglerfish by Harvard endocrinologists and in human physiology by a Danish physician in Copenhagen — has produced a class of drugs that reduces cardiovascular events, enables meaningful weight loss, facilitates Type 2 diabetes remission, and shows early promise in fatty liver disease, sleep apnoea, kidney disease, and addiction research.

The science, in this case, genuinely earned the hype. What needs to remain careful is how it translates into clinical practice — which patients, at what doses, with what support, and with what expectations. That is where the real work is.