GLP-1 Origin: Where GLP-1 Comes From and What Drugs Are Made Of (October 2026)

01 · The short answer

Where does GLP-1 come from?

GLP-1 comes from you. It is a hormone made by cells lining the lower gut, and it is released when food arrives. It tells the body to release insulin, slows the stomach and helps you feel full. Every person with a working gut produces it, whatever animal they have or have not eaten.

The medicines are a different matter. A GLP-1 drug is a manufactured molecule, shaped so that it acts on the same receptor but lasts far longer than the natural hormone. Our own medicine, Mounjaro, is the brand name for tirzepatide, a once-weekly injectable prescription medicine made by Eli Lilly.¹ It is not a venom extract, not an animal tissue product and not a herbal preparation.

02 · What to do next

Is this relevant to you?

If you are weighing up treatment, the origin of the molecule matters far less than whether the medicine is licensed, genuine and prescribed after a proper review. Mounjaro is licensed in the UK for weight management in adults and for type 2 diabetes.¹

When you are ready to look at treatment, our weight loss clinic explains how a consultation works, and the Mounjaro pen page shows live prices.

Related guide: Mounjaro country of origin.

03 · Natural GLP-1 in the body

How the body makes GLP-1 naturally

Your body makes GLP-1 in specialised cells in the lower intestine, and a smaller amount in the brainstem. The release is triggered by eating, especially food that reaches the lower gut. It is one of several signals the gut sends to coordinate digestion, blood sugar and appetite.

Natural GLP-1 does its job quickly and then disappears.

For a deeper look at what the hormone does across organs, see our guide to GLP-1 physiology, and for research on its effects in the brain, our page on GLP-1 and neuroinflammation.

04 · How GLP-1 was discovered

Who discovered GLP-1 and where?

No single nation owns the discovery.

This matters for the question people often ask, which is what country GLP-1 came from. The honest answer is that the hormone is universal to humans and the knowledge about it was built by an international scientific community.

The discovery was initially about diabetes. Its effects on appetite and stomach emptying were recognised as the research developed, and that is what eventually led to medicines for weight management as well.

Nothing in this story involves an animal being the source of the hormone. The animal chapter comes later, and it is smaller than the internet makes out.

05 · The Gila monster story

The Gila monster and lizard saliva story

The lizard story is true in a narrow sense.

An earlier diabetes medicine was developed from research into a protein in the saliva of the Gila monster. It is worth being precise about what this means. The medicine was based on the lizard protein's structure; it was not made by milking lizards. Drugs of this kind are produced in controlled manufacturing, not harvested from animals.

It also means the lizard link does not extend to the medicines most people ask about today. The idea that one lizard-derived discovery stands behind every GLP-1 product has been repeated so often that it now passes as fact. It is a simplification, and in the case of Mounjaro it is simply wrong.

Why did the story stick? Because it is memorable. If you see a page claiming your injection contains venom, treat it as a red flag for the quality of that page, not as a hidden truth about the medicine.

06 · What Mounjaro is made from

What is Mounjaro made from?

Mounjaro is a manufactured medicine whose active ingredient is tirzepatide, produced by Eli Lilly and supplied as a pre-filled multi-dose pen (KwikPen) in six strengths: 2.5mg, 5mg, 7.5mg, 10mg, 12.5mg and 15mg.¹ It is not extracted from a lizard, a snake or any other animal, and it is not a venom product.

Tirzepatide is designed rather than harvested. Its structure is built to engage gut-hormone receptors in the body, and the patient information leaflet lists the full ingredients of the pen if you want to see exactly what is in it.¹³ We would encourage anyone with an allergy or specific dietary concern to read that leaflet and raise it in the consultation.

How it works is the more interesting part. Tirzepatide is the first treatment of its kind to activate two natural gut-hormone receptors at once: GIP and GLP-1.¹ Together these help regulate appetite, slow how quickly the stomach empties, and improve the way the body responds to insulin. In practice, most people feel fuller sooner and less hungry between meals, which supports a reduced-calorie diet.

That dual action is what separates it from single-action GLP-1 medicines such as semaglutide, the ingredient in Wegovy and Ozempic. If you want to see how those compare in practice, our Wegovy pen page sets out the product. Both are licensed, both are manufactured, and neither is an animal-derived treatment.

07 · Ozempic, venom and lizards

Is Ozempic made from a lizard or snake venom?

No. Ozempic is a manufactured semaglutide medicine and is not made from lizard material or snake venom. Ozempic is semaglutide licensed for type 2 diabetes — it is not a UK weight-loss medicine, and prescribing it privately for weight loss is off-label. The confusion arises because the Gila monster discovery is often described as the origin of the whole drug class, which blurs together very different products.

Semaglutide and tirzepatide are once-weekly injections.

What about snake venom? Some medicines in other areas of medicine have been inspired by venom components, and that fact gets stretched into claims about weight-loss injections. It does not apply here. When people ask which drugs are made with snake venom, the answer is not Mounjaro, not Wegovy and not Ozempic. If a seller or social media post says otherwise, ask what evidence they are relying on; for licensed UK medicines, the product information is public.

One more caution: dramatic claims about secret ingredients are common in scam listings for counterfeit pens. A genuine pen comes from a regulated pharmacy after a prescriber has reviewed your health, and you can check any UK pharmacy on the GPhC register; ours is GPhC 9012878.⁷ Our piece asking whether GLP-1 treatment is a con goes further into the misinformation.

08 · Boosting GLP-1 naturally

Can you produce more GLP-1 naturally?

Your gut already releases GLP-1 every time you eat, but nothing you can eat will reproduce the effect of a prescription medicine. A balanced diet with plenty of protein and fibre and regular physical activity are sensible habits worth keeping whether or not you take a medicine.

The gap between that and a drug is large.

This is where supplements come in. Products marketed as nature's Ozempic or a poor man's Ozempic are low-cost supplements with no clinical oversight, and dosing is not standardised. They are not licensed as medicines for weight management, they are not tested in the trials behind Mounjaro, and we would not describe them as equivalent. The phrase poor man's Ozempic is a marketing label, not a recognised category of treatment.

If you are tempted, the safer step is to talk with a clinician about your options.

09 · Evidence behind the medicines

What the evidence says about the manufactured medicines

The proof that these medicines work does not come from their origin story; it comes from clinical trials. In the SURMOUNT-1 trial of 2,539 adults, people taking tirzepatide alongside diet and exercise lost on average 15% of their body weight on 5mg, 19.5% on 10mg and 20.9% on 15mg over 72 weeks, compared with 3.1% with lifestyle changes alone.²

These are trial averages, and individual results vary. Treatment works alongside a reduced-calorie diet and increased physical activity, not instead of them.² Trial averages do not predict your own result, so a prescriber will talk through realistic expectations with you instead of promising an outcome.

It is also worth saying what is not in the trial: nothing about lizards, venom or animals. The question regulators ask is whether a medicine is safe, effective and made to a consistent standard. That is why licensing, batch control and prescriber oversight matter far more than where the idea first came from.

Like all medicines, Mounjaro can cause side effects, and most are digestive. The most common, affecting more than 1 in 10 people, are nausea, diarrhoea, vomiting, constipation and abdominal discomfort. Serious side effects are uncommon but need urgent attention. Seek immediate medical help for: severe, persistent stomach pain that may spread to your back, with or without vomiting (possible pancreatitis); pain in the upper right abdomen, fever or yellowing of skin/eyes (possible gallbladder problems); or signs of a severe allergic reaction such as swelling of the face or throat and difficulty breathing. You can report suspected side effects through the MHRA Yellow Card scheme.¹⁹ If you are curious about how the wider pharmaceutical industry is involved, see our page on Regeneron and GLP-1.

10 · Who cannot take GLP-1

Who cannot take GLP-1 medicines?

Not everyone is suitable for a GLP-1 medicine, and that decision belongs to a prescriber who has reviewed your health history. Mounjaro is not suitable for everyone. You should not take it if you are allergic to tirzepatide or any of its ingredients, and it should not be used during pregnancy or while trying to conceive. Your prescriber will take extra care, or may recommend against treatment, if you have a history of pancreatitis, severe gut or digestive disease, diabetic retinopathy, or gallbladder problems. Always share your full medical history and medicine list during consultation.

Mounjaro is licensed for weight management in adults, used alongside a reduced-calorie diet and increased physical activity. For NHS use, NICE recommends it for adults with a BMI of at least 35 plus at least one weight-related condition, and the NHS primary-care rollout began in June 2025 with the highest-need groups first, initially BMI 40+ with four or more qualifying conditions.⁴ Access is being phased in over several years.

In a private consultation with us, a GPhC-registered prescriber reviews your answers and decides whether treatment is appropriate. Payment is taken when you place the order; if the prescriber decides the treatment is not suitable, the order is refunded automatically in full. The consultation is free, and the price shown is the price paid.

If you take other medicines, or you are on contraception, raise it. Mounjaro slows stomach emptying, which can reduce how well oral contraceptive pills are absorbed, and people on insulin or sulfonylureas may need their doses adjusted because of the risk of low blood sugar.⁷ The SmPC advises switching to a non-oral method, or adding a barrier method (such as condoms), for 4 weeks after starting Mounjaro and for 4 weeks after each dose increase.¹ Mounjaro must not be used during pregnancy, and it should be stopped at least one month before trying to conceive. If you become pregnant during treatment, stop the medicine and tell your prescriber promptly. Never stop or change a medicine without advice.