In the early 1990s, an endocrinologist named John Eng walked into his lab at a VA hospital in the Bronx with a vial of dried Gila monster venom. He'd ordered it from a mail-order catalog from a serpentarium in Utah [1].
His colleagues thought he was wasting his time. The idea that a poisonous desert lizard could teach us anything about human medicine seemed, to put it politely, unlikely.
But Eng had noticed something in the research literature that nobody else was paying attention to. And the compound he pulled from that venom would go on to become part of the most important drug class of the last twenty years. It was designed to treat diabetes. Then it caused dramatic weight loss. Then it reduced heart attacks. Then it helped people quit drinking. Then quit smoking.
And last month, a study showed it can do something that every medical textbook says is impossible.
Table of Contents
- The Monster
- The Rejection
- The Drug That Won't Stop
- The Tissue That Can't Heal
- "It's Just the Weight Loss"
- The Experiment
- What This Means
- References
The Monster
The Gila monster is one of only two venomous lizards on earth. It lives underground in the deserts of the American Southwest. And it has one of the strangest eating habits in the animal kingdom — it eats as few as three times a year, sometimes consuming up to a third of its body weight in a single meal [2].
And yet, between those rare feedings, its blood sugar stays perfectly stable. That fact caught Eng's attention.
In the late 1980s, researchers at the NIH had discovered that Gila monster venom had a pronounced effect on the pancreas — the organ that makes insulin. One of them, Jean-Pierre Raufman, described the kind of research he was engaged in as a "fishing expedition" that grant committees today would probably dismiss. He later said he "would never have conceived that there was any potential therapeutic benefit" [3].
But Eng saw something they didn't. He'd been trained by Rosalyn Yalow — the Nobel Prize winner who invented a technique for detecting tiny amounts of hormones in the blood. He turned that same technique on the lizard venom [4].
In 1992, he found a compound that had never been documented before. He called it exendin-4 [4].
It was 53% identical to a human hormone called GLP-1 — a hormone that tells the pancreas to release insulin when blood sugar rises [5].
But there was one crucial difference. Natural GLP-1 breaks down in your body within two minutes. It's gone almost as soon as it appears [6]. Exendin-4 — the lizard version — lasted for hours in mice [4].
That meant you could potentially inject it and have it work all day. For someone with type 2 diabetes, that could be transformative. Eng had found, in a vial of dried lizard venom ordered from a catalog, what might be a new way to treat one of the most common diseases on earth.
But there was a problem. Nobody wanted it.
The Rejection
Eng filed a patent in 1993. He paid for it himself — out of his own pocket — because the VA refused to patent it. It didn't address a "veteran-specific ailment" [4][7].
That put him in a difficult position. He bore the expenses of patenting his discovery with no guarantee that anything would come of it.
Then he spent three years trying to convince pharmaceutical companies to develop it. A peptide drug derived from lizard venom? The concept seemed absurd by industry standards. Peptide drugs had a reputation for being expensive, hard to manufacture, and inconvenient for patients [4].
Jens Juul Holst, one of the world's leading GLP-1 researchers, later described Eng's situation bluntly: "He was extremely frustrated. Nobody was interested in his work. It was too strange for people to accept" [4].
Three years of rejection. Then, in September 1996, Eng presented a poster at a diabetes conference in San Francisco. A researcher named Andrew Young from a small biotech company called Amylin Pharmaceuticals stopped to read it. One month later, Amylin licensed the patent [4].
Nine years after that — in April 2005 — the FDA approved Byetta. The first GLP-1 drug ever made. Derived from Gila monster venom. Developed from a poster that almost nobody stopped to look at [8].
But Byetta was a modest drug. A twice-daily injection that helped control blood sugar with about 5% weight loss. Useful, but unremarkable. Nobody suspected what would come next [8][9].
The Drug That Won't Stop
Eng's discovery proved something critical: targeting the GLP-1 receptor works. That proof-of-concept opened the door for larger pharmaceutical companies to engineer more potent versions.
Novo Nordisk developed liraglutide — Victoza — approved in 2010. Once daily instead of twice daily [10]. Then came semaglutide — Ozempic — approved in 2017. Once weekly. Each generation more potent, longer-lasting [11].
And then the surprises started.
Weight loss. Patients on Ozempic were losing 15% of their body weight. It wasn't designed to do that. People were losing weight at rates previously only seen with bariatric surgery [12].
The FDA approved semaglutide, branded as Wegovy, specifically for obesity in 2021 [13].
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Get Your Personalized Health PlanAnd after weight loss, other surprising effects started showing up in multiple areas.
Like heart disease. The SELECT trial — a massive randomized controlled trial — showed that semaglutide reduced major cardiovascular events by 20% in people with obesity who did not have diabetes. A drug designed for blood sugar was protecting hearts [14].
Harvard Medical School's Josephine Li commented, "What was surprising and amazing was they were found to reduce the risk of major adverse cardiovascular events" [15].
But maybe that was just because the patients lost weight? Less weight, less strain on the heart? That was a reasonable explanation — until the next set of findings made it harder to sustain.
They were linked to addiction. A large VA study found that patients on GLP-1 drugs had significantly lower rates of substance abuse. Problems fell by 18% for alcohol, 20% for nicotine, and 25% for opioids [16].
UAB neuroscientist Andrew Hardaway explained: "Food simply becomes less rewarding. You still enjoy eating, but it doesn't drive behavior in the same way" [17]. The same mechanism seemed to be dampening the brain's reward response to alcohol, nicotine, and opioids.
This wasn't a weight loss effect. This was something acting on the brain.
Then there's kidney disease. The FLOW trial showed semaglutide reduced risks and slowed disease progression — and the benefits appeared even in patients who didn't lose significant weight [18].
Researchers started finding GLP-1 receptors widely distributed across many tissues — not just the gut and pancreas, but in the brain, the heart, and the kidneys [19].
Nils Kruger, of Harvard Medical School, captures the feeling of many researchers: "It's just astonishing how many indications those medications seem to be effective for or have some beneficial effects" [15].
Decades of basic science. Starting with one endocrinologist and a vial of lizard venom.
But even Kruger couldn't have predicted what came next. Because the next discovery challenges something doctors have believed since 1743.
The Tissue That Can't Heal
In that year, a Scottish surgeon named William Hunter stood before the Royal Society in London and made a declaration that would define orthopaedic medicine for the next three centuries: "From Hippocrates to the present age, an ulcerated cartilage is universally allowed to be a very troublesome disease; when destroyed, it is never recovered" [20].
For 283 years, every doctor who's looked at a worn-out knee has told their patient some version of the same thing.
And there's a straightforward reason why. Cartilage has no blood supply. No nerves. No efficient way to deliver the cells and nutrients needed to grow new tissue. It's one of the few structures in the human body that, once damaged, is severely limited in its ability to repair itself [21].
That hasn't stopped people from trying. Techniques like microfracture — drilling tiny holes into the bone beneath damaged cartilage to stimulate bleeding — have been developed. And we're making progress in various kinds of surgical interventions. And yet, at present, available treatments are far from satisfactory for many [22].
So what do the 600 million people worldwide with osteoarthritis typically get [23]? A treatment ladder that manages symptoms without fixing the underlying problem. Painkillers. Steroid injections. And when those stop working — knee replacement surgery. At an average cost of about $20,000 in the US [24].
Karin Payne, associate professor of orthopaedics at the University of Colorado, put it plainly: "There's no cure for osteoarthritis. There aren't even treatments that slow down the disease progression" [25].
But then patients on Ozempic started saying something that their doctors initially dismissed. Their joints felt better. Not just less pain from carrying less weight. Something else. Something unexpected.
"It's Just the Weight Loss"
The obvious explanation was weight loss. Less weight means less mechanical pressure on joints. Every kilogram you lose takes roughly four kilograms of stress off your knees [26].
So when Ozempic patients reported less joint pain, doctors shrugged: of course your knees hurt less — you lost 30 pounds.
The STEP 9 trial, published in the New England Journal of Medicine in 2024, seemed to confirm this. 407 patients with obesity and knee osteoarthritis. After 68 weeks, pain scores dropped 42 points with semaglutide compared to 28 with placebo. But patients also lost 13.7% of their body weight [27].
Case closed. Or so everyone thought.
But a team of researchers at the Shenzhen Institutes of Advanced Technology — part of the Chinese Academy of Sciences — wasn't satisfied with that explanation. Led by Di Chen, they designed an experiment that would test it directly.
The Experiment
This is the study that changes the conversation [28].
Chen's team took mice with osteoarthritis and split them into groups. One group received semaglutide. Another group was pair-fed — meaning they were given restricted calories, carefully controlled so they lost the exact same amount of weight as the semaglutide group. Same weight loss. No drug [28].
If the joint improvements were "just the weight loss," both groups should look the same.
They didn't. The pair-fed mice lost the same weight. But their cartilage kept deteriorating. Only the semaglutide group showed preserved cartilage, reduced inflammation, and fewer bone spurs. Same weight loss — completely different outcomes in the joints [28].
Di Chen explained the implications: "This controlled experiment demonstrates that semaglutide's protective effect on cartilage in osteoarthritis is independent of weight loss, challenging the traditional belief that osteoarthritis improvement relies solely on weight reduction" [29].
So if it's not weight loss, what's happening?
Here's the simplest way to think about it. Your cartilage cells — called chondrocytes — need energy to maintain and repair the tissue around them. In osteoarthritis, those cells get stuck running on an inefficient fuel source. Think of it like a factory running on a sputtering generator. It's barely enough energy to keep the lights on. Not nearly enough to rebuild anything.
What semaglutide does is flip a switch inside those cells that upgrades them to a clean, efficient energy source that produces dramatically more energy, enough to actually start repairing.
The technical pathway: GLP-1 receptors — which nobody expected to find on cartilage cells — activate the AMPK-PFKFB3 signalling cascade, shifting the cells from glycolysis to oxidative phosphorylation [28].
The GLP-1 receptor on cartilage cells — a receptor nobody was looking for — triggers the cells to start rebuilding the tissue around them.
But mouse cartilage isn't human cartilage. Does it actually work in people?
Chen's team ran a pilot clinical study. 20 patients aged 50 to 75, all with obesity and knee osteoarthritis. Half received standard treatment — hyaluronic acid injections. The other half received hyaluronic acid plus weekly semaglutide [28].
After 24 weeks, they put them in MRI scanners. The semaglutide group showed an average 17% increase in cartilage thickness, suggesting regeneration. The control group: less than 1%. The thickened cartilage was visible in weight-bearing areas of the knee — the areas that take the most punishment [28].
Patients also experienced reduced pain and improved joint function. The tissue that William Hunter said was "never recovered" — that every orthopaedic textbook calls irreplaceable — appeared to be growing back [28].
The study results open the possibility of a radical new approach to osteoarthritis. We already know we can reduce pain through weight loss. It now appears we may also be able to actually regenerate cartilage.
What This Means
I need to be honest about the limitations. This was a pilot study — 20 patients, 24 weeks. We don't know if cartilage actually regrew or thickened for other reasons. If it did regrow, its durability is an open question. We don't know if it's functionally the same as original cartilage. We don't know if it works at different stages of osteoarthritis or in people who aren't obese. Much larger, longer trials are needed.
The study authors themselves wrote: "The protective effects of semaglutide on the human knee joint should be interpreted with caution and require further validation" [28].
But the pair-fed mouse experiment is what makes this more than just another small study. It doesn't just show correlation — it demonstrates a mechanism that works independently of weight loss. Something is happening at the cellular level. And it's consistent with the broader pattern we keep seeing with this drug class: GLP-1 receptors turning up in places nobody expected, doing things nobody predicted.
In 1990, John Eng ordered dried lizard venom from a catalog and found a compound that nobody wanted. That compound led to a drug class that now treats diabetes, obesity, heart disease, and addiction. Annual sales exceed $70 billion. And it may have just done something that a surgeon in 1743 said was impossible.
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Discoveries like cartilage regeneration are reshaping what we know about prevention. The Health Roadmap turns the latest research into evidence-based suggestions tailored to your goals.
Get Your Personalized Health PlanReferences
1. https://peptideinitiative.com/peptide-chronicles/exenatide
2. https://www.zmescience.com/ecology/animals-ecology/gila-monster-ozempic-origin/
3. https://whyy.org/segments/ozempic-how-gila-monster-venom-led-to-weight-loss-drugs/
4. https://en.wikipedia.org/wiki/Exenatide
5. https://pubmed.ncbi.nlm.nih.gov/15866711/
6. https://www.frontiersin.org/journals/endocrinology/articles/10.3389/fendo.2024.1431292/full
9. https://pmc.ncbi.nlm.nih.gov/articles/PMC3241299/
10. https://www.nejm.org/doi/full/10.1056/NEJMp1001578
12. https://www.nejm.org/doi/full/10.1056/NEJMoa2032183
14. https://www.nejm.org/doi/full/10.1056/NEJMoa2307563
15. https://news.harvard.edu/gazette/story/2026/02/whats-next-for-glp-1s/
16. https://www.bmj.com/content/392/bmj-2025-086886
18. https://www.nejm.org/doi/full/10.1056/NEJMoa2403347
19. https://pmc.ncbi.nlm.nih.gov/articles/PMC9455625/
21. https://pmc.ncbi.nlm.nih.gov/articles/PMC10071204/
22. https://www.mdpi.com/1648-9144/61/1/24
23. https://www.thelancet.com/journals/lanrhe/article/PIIS2665-9913(23)00163-7/fulltext
24. https://pmc.ncbi.nlm.nih.gov/articles/PMC10368258/
25. https://news.cuanschutz.edu/medicine/arthritis-glp-1-agonists-obese-patient
26. https://pubmed.ncbi.nlm.nih.gov/15986358/
27. https://www.nejm.org/doi/abs/10.1056/NEJMoa2403664
28. https://www.cell.com/cell-metabolism/fulltext/S1550-4131(26)00008-2
