Weight Loss Injections in Cardiff: Making the Right Choice

Which injection is which, and why the difference matters for you

The two licensed options are not interchangeable. Tirzepatide, sold as Mounjaro, is a dual GIP and GLP-1 receptor agonist, the only weight-management medicine in the UK to activate both pathways simultaneously. Semaglutide, sold as Wegovy, targets the GLP-1 pathway alone. Both slow gastric emptying and reduce appetite, but the dual mechanism is one reason tirzepatide's trial results edge ahead. In the SURMOUNT-5 head-to-head trial, published in the New England Journal of Medicine in 2025, tirzepatide produced greater average weight reduction than semaglutide 2.4mg over 72 weeks.

That gap is not the whole story, though. Semaglutide also now has a 7.2mg maintenance dose approved by the MHRA (April 2026), which in trials produced around 20.7% average weight loss, narrowing the distance considerably. A fuller comparison of how the two injections differ in mechanism, evidence and tolerability is covered on the difference in weight loss injections page, which goes into the head-to-head data in more detail. Your own medical history, any medicines you already take, and how your body tolerates the titration schedule will all factor in. A prescriber weighs those things; a price comparison site does not.

One practical note: if you are exploring what weight loss injections are available and how they work, it helps to know that both injections start at a low dose and increase gradually over several weeks. The starter doses exist to reduce the chance of GI side effects, they are adjustment doses, not the doses at which the full clinical effect is seen.

Who these injections are licensed for, and what eligibility actually means

The private licensed eligibility criteria come from each medicine's UK Summary of Product Characteristics. For both Mounjaro and Wegovy, the core thresholds are a BMI of 30 or above, or a BMI of 27 or above alongside at least one weight-related condition such as high blood pressure, high cholesterol, type 2 diabetes, prediabetes, or obstructive sleep apnoea. Lower BMI thresholds apply for certain ethnic backgrounds under UK guidance. Meeting those numbers is a starting point, not a guarantee, a prescriber also reviews your full health picture, current medicines, and any contraindications before recommending treatment.

Neither injection is licensed for under-18s. Both are not recommended during pregnancy, whilst breastfeeding, or if you are actively trying to conceive. Certain conditions (including a personal or family history of medullary thyroid carcinoma or MEN2, and some gastrointestinal conditions) require prescriber discussion. If you are unsure where you sit, the weight loss treatment overview walks through the eligibility landscape in plain terms, and the FAQs cover common sticking points.

The NHS has its own criteria for accessing these medicines, which are stricter and phased. Currently, tirzepatide on the NHS requires a BMI of 40 or above plus four or more specific weight-related conditions; a second cohort (BMI 35–39.9) became eligible from June 2026. For those who do not meet NHS criteria, or who would rather not wait, a regulated private prescription route exists. The where to buy weight loss injections page explains what to look for in any provider, and what the red flags are.

Side effects: what the evidence says and when to seek help

The most commonly reported side effects across both injections are gastrointestinal: nausea, loose stools, constipation, indigestion, and burping. Fatigue and headache are also noted. For most people these are mild to moderate and ease as the body adjusts, particularly after the first few weeks at a new dose. Rotating your injection site between the abdomen, thigh and upper arm (and keeping to the same day each week) supports consistent tolerability. A set of alcohol swabs for site preparation is a small but useful habit to build in from the start.

There are rarer but serious effects to be aware of. The MHRA issued a Drug Safety Update in January 2026 highlighting acute pancreatitis as a known, infrequent but potentially serious risk: severe stomach pain that reaches through to the back, with or without vomiting, warrants urgent medical attention rather than waiting to see if it settles. Gallbladder symptoms, signs of dehydration from prolonged vomiting or diarrhoea, and any allergic reaction should also prompt immediate contact with a healthcare professional. You can report suspected side effects directly through the MHRA's Yellow Card scheme. A full side-effect profile for each medicine is published on the NHS tirzepatide medicines page, worth reading before you start.

If you already take an oral contraceptive, tirzepatide specifically may reduce pill absorption during the first four weeks of treatment and for four weeks after each dose increase; adding a non-oral method of contraception during those windows is the recommended approach per MHRA guidance. Raise this with your prescriber at consultation.

Getting a prescription: what a regulated route looks like

Many people in Cardiff start by looking at what a local clinic or GP can offer, then discover that NHS waiting lists are long and private clinics vary considerably in how thoroughly they assess patients. The critical thing (wherever you go) is that a qualified prescriber personally reviews your case. An overview of how the three main prescription weight-loss injections compare on access and evidence may be useful if you are still deciding between options.

At nume, consultations are reviewed the same day by a GPhC-registered Independent Prescriber, a real clinician reading your answers, not automated triage. Identity and weight are verified before any prescription is issued, and our pharmacy holds GPhC premises registration 9012878, verifiable directly on the GPhC register. Orders placed by noon Monday to Friday are dispatched the same day once approved, arriving with DPD the next working day in plain packaging, which matters if you work shifts or need to be home before the school run. If you want to understand how a single weight loss injection fits into a broader treatment plan, including what to expect at each stage of the titration schedule, that page covers the process in detail. The cost context for private treatment, including what a transparent price should include, is set out on the weight loss injections cost guide. When you are ready to talk to a prescriber about whether treatment is right for you, start your free consultation here.