Tummy injection for weight loss: what clinical trials found

What the trial data actually established about these injections

The SURMOUNT-1 trial, published in the New England Journal of Medicine, randomised 2,539 adults with obesity over 72 weeks. At the highest tirzepatide dose, average body-weight loss was around 20–21%, with some analyses reaching approximately 22.5%. Those are averages across a large, real-world-adjacent population, not best-case outliers. The STEP 1 trial, also published in the NEJM, followed adults taking semaglutide 2.4mg weekly for 68 weeks and found around 15% average weight reduction. In a direct head-to-head comparison (the SURMOUNT-5 trial, published in 2025), tirzepatide produced greater average loss than semaglutide 2.4mg over 72 weeks.

Both trials used subcutaneous injections, just under the skin, not into muscle, and not intravenous. Participants could choose the abdomen, thigh or upper arm. The abdomen tends to be the most accessible site to reach yourself, which is part of why it's the one most people end up using week after week. None of this means the medicine works differently depending on where you inject; rotation matters for skin health, not for efficacy.

One thing the trials also confirmed: results are significantly better alongside a reduced-calorie diet and regular physical activity. The medicine changes the hormonal environment that drives hunger, it doesn't override every other variable.

Why 'tummy injection' is not the same as a fat-dissolving treatment

A question our prescribers hear most weeks is whether these injections work by dissolving fat at the injection site. They don't. Tirzepatide and semaglutide are systemic medicines; once injected under the skin, they enter the bloodstream and act on receptors in the gut, pancreas and brain. The appetite-suppressing, gastric-emptying-slowing effect is body-wide. Injecting into the abdomen rather than the thigh does not target abdominal fat specifically.

This is worth being clear about because a separate category of products (sometimes marketed as 'fat-dissolving injections' or 'lipolytic injections') work on a completely different principle and are not the same thing. The NHS patient information on tirzepatide describes the mechanism accurately: it acts on hormone receptors, not on fat cells directly. The weight loss that results from reduced appetite and improved metabolic signalling tends to come from all over the body over time.

If you've seen the phrase 'skinny jab' used to describe these medicines, that's a colloquialism that papers over some important nuance. The mechanism is sophisticated; the injection technique itself is straightforward.

Injection-site rotation and what it means in practice for the abdomen

Rotating sites isn't a bureaucratic rule, it prevents lipohypertrophy, a localised thickening of fatty tissue that develops when the same small patch of skin is repeatedly punctured. Injecting into a hardened area reduces absorption and can affect how the medicine works. For the abdomen specifically, the guidance is to avoid the area immediately around the navel and to shift the injection point by at least a centimetre each week within that zone.

Both Mounjaro and Wegovy pens are pre-filled; the needle is short and fine. Many people find the first injection is less daunting than they expected. Cleaning the site with an alcohol swab beforehand is good practice, alcohol swabs are available if you need them separately. The pen goes in, the dose is delivered, and the whole thing takes under a minute. Storage is refrigerated (check the Patient Information Leaflet for the exact room-temperature window if you need to travel).

If you're considering these treatments and want to understand the full picture of what's involved, the weight-loss injection overview on our site covers the practical detail. You can also read more about the injections licensed for weight management in the UK before making any decision.

Who can access these medicines and through which routes

The licensed eligibility for both tirzepatide and semaglutide is broadly: adults with a BMI of 30 or above, or 27 and above alongside at least one weight-related condition such as hypertension, prediabetes, high cholesterol or obstructive sleep apnoea. Lower BMI thresholds apply for some ethnic backgrounds under UK clinical guidance. BMI alone doesn't determine approval; the prescriber considers your full medical picture, current medicines and any contraindications.

NHS access exists but is phased and restricted. Tirzepatide on the NHS currently requires a high BMI alongside multiple qualifying conditions; waiting lists for Wegovy through specialist services are commonly long. Many people exploring weight management treatment privately do so because they meet the clinical criteria but don't meet the NHS thresholds yet, or simply don't want to wait.

If you order before noon on a working day and are approved, treatment is dispatched the same day by DPD. Some people time their first order for a Monday, it's a clean start to the week, and if payday has just landed, the decision isn't sitting in a mental queue. The pen arrives in plain packaging the next working day. For a breakdown of what the service costs and what that covers, the treatment cost information page is the clearest place to look.

These medicines are also subject to ongoing MHRA monitoring, and a safety note worth being aware of: the MHRA issued a Drug Safety Update in January 2026 on GLP-1 medicines and acute pancreatitis. Severe, persistent stomach pain that radiates to the back warrants urgent medical attention. Our clinical team is available seven days a week for aftercare questions, and you can reach us via the contact page at any point. If you have questions about a specific weight loss injection r option, or want to explore what m injection for weight loss involves, those pages cover each in more depth than the general safety questions page.

Our prescribers include GPhC-registered Independent Prescribers who review every consultation personally, your answers are read by a clinician, not processed by an automated system. If you'd like to find out whether you're eligible, you can read about the three weight loss injections available before speaking to our prescribers as a natural next step.