What semaglutide is derived from — and why that origin matters

You've heard it called a 'natural' medicine (here's what that actually means

A question that comes up regularly goes something like this: 'I read that Wegovy is based on something the body already makes) is that true?' The answer is yes, with important caveats. Semaglutide mimics GLP-1, a hormone produced in the small intestine. After a meal, specialised gut cells release GLP-1 into the bloodstream, where it signals to the brain that food has arrived, slows the rate at which the stomach empties, and prompts the pancreas to manage blood sugar. Your body does this already, every single day.

The catch is that natural GLP-1 is a brief messenger. Enzymes called DPP-4 clear it from the circulation within two to three minutes. That's fine for the body's purposes (it sends its signal and steps aside) but it makes natural GLP-1 completely impractical as a medicine. You'd need injections every hour.

So researchers at Novo Nordisk worked from the human GLP-1 sequence and made two key changes. First, they swapped out one amino acid near the molecule's core (position 8, for those who like the detail), which stops DPP-4 recognising it as a target. Second, they attached a long fatty-acid chain. That chain lets semaglutide bind loosely to albumin (a protein that drifts slowly around the bloodstream) which both protects it further and extends its half-life to around one week. A once-weekly injection becomes possible. You can read a plain-English overview of how this works on the semaglutide explained page.

One gentle correction worth making: the hormone it's based on is human, not animal. If you're wondering what semaglutide is made from, it isn't extracted from any creature; it is synthesised in a laboratory using recombinant DNA technology. The 'natural origin' story is real, but the medicine itself is manufactured.

From Gila monster to gut hormone, the wider backstory

It's genuinely interesting science, and it occasionally surprises people. The earliest GLP-1 receptor agonists, developed in the 1990s, were inspired by a peptide called exendin-4 found in the saliva of the Gila monster lizard. That peptide happened to activate the same receptor as human GLP-1, and it was naturally resistant to DPP-4, a quirk that gave researchers their first clue that a longer-acting GLP-1 drug was chemically feasible.

Semaglutide itself is not derived from lizard biology. It is built directly from the human GLP-1 template, refined over years of laboratory work. The Gila monster is part of the field's origin story, not semaglutide's own family tree. This distinction matters if you are weighing up what the medicine is.

The end product is a fully synthetic molecule produced by pharmaceutical manufacturing, assessed for safety and efficacy in large clinical trials before UK licensing. The STEP 1 trial, published in the New England Journal of Medicine, randomised 1,961 adults and found average body-weight reduction of around 15% over 68 weeks at the 2.4mg maintenance dose, results that formed the basis of the UK marketing authorisation. You can find a broader overview of what semaglutide is and does on the semaglutide treatment page.

How the molecule's origin shapes what it does (and what side effects feel like)

Because semaglutide is acting on a receptor your body already has and uses, many of its effects feel like an amplified version of normal post-meal physiology. Appetite settles. Meals feel satisfying sooner. The stomach takes longer to empty. For most people, the first few weeks bring some nausea, loose stools or indigestion, the same system that tells you when you've overdone it at dinner is now being activated more persistently than usual. The NHS medicines pages for semaglutide list the common side effects clearly and are worth reading before you start.

These GI effects are, for most people, temporary. They tend to be most noticeable when treatment begins or after a dose step, then settle as the body adjusts. Staying well hydrated and eating smaller, lower-fat meals during the early weeks helps considerably, something our prescribers often discuss during aftercare check-ins.

If you're curious about how the cost of treatment fits into the decision, the Wegovy cost context page covers what a legitimate private prescription typically includes and why the headline price isn't always the full picture. For a closer look at what the Wegovy injection contains at a formulation level, the Wegovy ingredients page goes into that detail.

Semaglutide is a prescription-only medicine in the UK. A prescriber decides whether it is appropriate for a given person, at what dose to begin, and how to adjust it over time, GLP-1 biology is the foundation, but the clinical picture is always individual. Questions about how the medicine interacts with your body's chemistry, including whether Wegovy affects potassium levels, are worth raising with your prescriber before you begin. If you'd like to explore whether Wegovy could be suitable for you, check your eligibility with our clinical team.