Weight loss injections in Warrington: the clinical picture

What the clinical trials showed, and what that means in practice

The SURMOUNT-1 trial, published in the New England Journal of Medicine, randomised 2,539 adults with obesity and no diabetes to tirzepatide or placebo over 72 weeks. At the highest dose studied, participants lost an average of around 20–21% of their body weight, a figure that sits well above what older treatments typically produced. Semaglutide's phase 3 programme reported average losses of roughly 15% over 68 weeks at the 2.4mg maintenance dose. Neither of those numbers is a promise; they are population averages from controlled conditions with structured diet and activity support alongside the medicine.

What those averages do tell us is that these medicines work through biology, not willpower. Both activate receptors involved in appetite signalling in the gut and brain, reducing hunger and slowing gastric emptying. The effect compounds over months, which is why the dosing schedule starts low and increases gradually under prescriber supervision. You can read more about how weight loss injections work if you'd like a fuller explanation of the mechanism before deciding anything.

NICE has formally recommended tirzepatide for adults with a BMI of 35 or above alongside at least one weight-related health condition, and semaglutide within specialist weight management services on similar criteria. Both carry a Black Triangle (▼) designation, meaning the MHRA continues to collect safety data beyond the original trial programme.

Eligibility: what the licensed criteria cover

The licensed criteria for both medicines are set by the medicines' UK marketing authorisations, not by individual clinics. In broad terms, both are licensed for adults with a BMI of 30 or above, or a BMI of 27 or above with at least one weight-related condition such as high blood pressure, high cholesterol, obstructive sleep apnoea, prediabetes or type 2 diabetes. Lower BMI thresholds apply for some ethnic backgrounds under UK clinical guidance.

BMI alone doesn't settle the question. A prescriber also considers your medical history, current medicines and any contraindications before approving treatment. Pregnancy, breastfeeding and actively trying to conceive are situations where neither medicine is recommended; the same applies to anyone under 18. Certain conditions (including a personal or family history of medullary thyroid carcinoma) require careful prescriber discussion before these medicines are considered.

If you're unsure whether you'd be eligible, the process for getting weight loss injections in the UK is worth reading through first. A free consultation with a prescriber is the only way to get a definitive answer for your individual circumstances.

Side effects worth knowing before you start

The most commonly reported side effects across both medicines are gastrointestinal. Nausea tends to be the one people notice first, along with loose stools, constipation, indigestion and occasionally vomiting. These effects are typically most pronounced after starting or after a dose increase, and for most people they settle within a week or two as the body adjusts. Starting at a low dose and titrating slowly is specifically designed to reduce this burden.

A small number of people experience more serious reactions. The MHRA issued a Drug Safety Update in January 2026 highlighting acute pancreatitis as an infrequent but potentially serious risk: if you develop severe, persistent stomach pain that spreads to your back, seek urgent medical attention. You can report any suspected side effect through the MHRA Yellow Card scheme. For a fuller safety picture, the warnings and side effects page covers the full profile, including the contraception interaction that applies specifically to tirzepatide. It is also worth reading what UK doctors have warned about weight loss injections, since their clinical perspective adds useful context beyond the trial data.

One practical note on what to expect: when your first pen arrives by DPD (tracked, in plain unbranded packaging) it comes with a patient information leaflet that covers storage, injection technique and what to watch for. Read it before you start. It is the definitive reference for your specific medicine.

NHS access versus a regulated private pharmacy

NHS access to these medicines is phased and criteria-based. As of summer 2026, tirzepatide is available on the NHS for adults with a BMI of 40 or above alongside four or more qualifying conditions; the next phase, which opened in June 2026, extends to BMI 35–39.9 with four or more conditions. Even where someone meets those criteria, their GP practice needs to have opted into the prescribing scheme, and all NHS patients must engage with structured diet and activity support. NHS England's guidance on weight-management injections sets out the full picture.

For people who don't meet the NHS criteria, or who would rather not wait, a regulated online pharmacy is the main private route. The key check is the GPhC register: any online pharmacy operating legally in the UK must appear on it. You can look up which weight loss injections are available through regulated UK pharmacies and what a legitimate service looks like before you commit to anything.

Pricing for private treatment varies by dose and provider. If you want to compare the options side by side, a helpful starting point is to review the three weight loss injections currently available in the UK, so you can see how they differ before making any decisions. For broader context on what the market looks like and what a transparent price should include, the treatment overview gives a plain summary. What matters most for a prescription medicine isn't the lowest headline figure, it's confirmed clinical assessment, genuine supply chain and ongoing support if you need it. If you'd like to discuss your situation with a prescriber, you're welcome to speak to our prescribers through a free consultation at a time that suits you.