GLP-1 Gene: What GCG and GLP1R Do (October 2026)

01 · The short answer

Which gene is the GLP-1 gene?

The honest answer is that two genes matter, and neither is called “GLP-1”. GCG is the gene that produces proglucagon, a larger precursor protein. GLP1R is the gene that produces the receptor, the docking point on a cell that the hormone fits into.

Think of it as a key and a lock. GCG helps make the key. GLP1R builds the lock. Weight-loss medicines are designed to fit that lock, and tirzepatide, the active ingredient in Mounjaro, also fits a second lock for the hormone GIP.¹

02 · What to do with this

Does my genetic makeup decide whether treatment works?

Not in any way you can currently test for in routine UK care. Researchers are studying whether small variations in genes such as GLP1R may influence how strongly someone responds to these medicines. That work is ongoing, and it does not yet change who is prescribed what.

Eligibility for treatment is based on your body mass index, your health conditions and a prescriber’s review, not on a gene result. The licensed criteria and your medical history are what count. Our weight loss pages explain who the medicine is for, and the Mounjaro pen page lets you start a free consultation reviewed by a GPhC-registered prescriber.

03 · GCG gene and proglucagon

The GCG gene and proglucagon

The GCG gene carries the instructions for proglucagon, a precursor protein. A precursor is a first draft: it is cut into different active pieces depending on which cell is reading it.

In specialised cells of the gut, proglucagon is cut to release GLP-1.

04 · GLP1R receptor gene

The GLP1R gene and the receptor

GLP1R is the gene that builds the GLP-1 receptor. The receptor sits on the surface of cells and passes a message inside when the hormone, or a medicine that mimics it, attaches.

Everyone carries a GLP1R gene. People differ slightly in its exact sequence, as they do for most genes, and scientists are examining whether certain variants change how well the receptor responds. At present that is a research question, not a clinical test. For more on this receptor class, see our explainer on the GLP-1 GPCR.

05 · Does GLP-1 change DNA?

Does GLP-1 change your DNA?

No. Neither the natural hormone nor GLP-1 medicines rewrite your genes. They work by binding to receptors and changing the signals cells send, which is a very different process from altering DNA.

In practice, tirzepatide activates two natural gut-hormone receptors, GIP and GLP-1. Together these help regulate appetite, slow how quickly the stomach empties, and improve the way the body responds to insulin.¹

06 · Gene therapy claims

Is there GLP-1 gene therapy?

Not as a licensed UK treatment. Gene therapy means delivering genetic material to change how cells behave. The licensed GLP-1 treatments on the UK market are conventional medicines taken by injection or tablet.

Be cautious of any seller using the words “gene therapy”, “gene activation” or “reprogram your GLP-1 genes” for a weight-loss product. A legitimate prescription medicine is supplied only after a consultation reviewed by a prescriber. A seller offering to supply without a consultation or prescription is a warning sign. Report any suspected side effect through the MHRA Yellow Card scheme.⁷

Supplements marketed with genetic or “natural GLP-1” language are low-cost products with no clinical oversight, and their effects are not comparable with licensed medicines. For a related question about another hormone-type drug, see whether pramlintide is a GLP-1.

07 · Natural GLP-1 and food

Where does natural GLP-1 come from?

Natural GLP-1 comes from specialised cells in the lining of your intestine, which release it when food arrives. Protein, fibre-rich foods and healthy fats are commonly discussed as foods that reach those cells.

Eating a balanced, high-protein, high-fibre diet is sensible for many reasons. Food alone should not be expected to replicate treatment.

No single food switches on fat-burning hormones. Be sceptical of any claim built around one ingredient or ritual. Sustainable weight management rests on diet, activity, sleep and, where appropriate, medical treatment.

08 · GLP-1 and the brain

What does GLP-1 do in the brain?

GLP-1 and GIP help regulate appetite, which is part of how these medicines reduce hunger. The practical result for most people is feeling fuller sooner and less hungry between meals, which supports a reduced-calorie diet.¹

Medicines in this class are used alongside diet and activity, not instead of them. If you have thoughts of harming yourself or ending your life, get help straight away. Call 999 or go to A&E if you are in immediate danger. In England you can call NHS 111 and choose the mental health option, any time. You can also call Samaritans free on 116 123, day or night. Tell your prescriber about any change in your mood while taking Mounjaro, and report any unexpected symptom through the Yellow Card scheme.¹⁹

09 · From genes to treatment

From genes to treatment: what the evidence shows

Evidence for these medicines comes from large trials, not gene studies. In SURMOUNT-1, 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.

Averages hide a spread of responses. Some people respond strongly and some less so.

NHS access is being phased in over several years, with NICE guidance setting out who qualifies first.⁴⁶ Many people who meet the licensed criteria choose regulated private treatment instead of waiting. Our GLP-1 therapy cost information page explains what to budget, and the Mounjaro pen starts at £169.99 per month at the standard 2.5mg price.

10 · Research and measuring GLP-1

Testing and research into GLP-1 genetics

Laboratories can also measure the hormone itself in blood samples using specialised methods. Our explainer on the GLP-1 assay describes how that works and why it is mainly a research tool.

For someone deciding whether to start treatment, the practical takeaway is simple: you do not need a genetic or hormone test first. A prescriber reviews your health history and decides whether treatment is suitable.

Wider uptake of these medicines is a separate topic, covered in our piece on GLP-1 adoption.