The Most Common Weight Loss Injections Available in the UK

The biggest misconception: that all weight loss injections are essentially the same

Many people researching common weight loss injections assume the different brand names are mostly marketing. They are not. Tirzepatide (Mounjaro) is the only dual GIP and GLP-1 receptor agonist licensed for weight management in the UK, meaning it activates two separate gut-hormone pathways involved in appetite regulation and blood-sugar control. Semaglutide (Wegovy) is a single GLP-1 receptor agonist, a real and meaningful structural difference, not a branding detail.

That distinction shows up in the clinical trial results. In SURMOUNT-1, tirzepatide produced an average body-weight reduction of around 20–21% over 72 weeks at the highest dose, across thousands of adults with obesity. The STEP 1 trial for semaglutide 2.4mg reported around 15% average weight loss over 68 weeks. Both figures come from rigorous trials published in the New England Journal of Medicine, and both are averages, individual responses vary considerably. In the more recent SURMOUNT-5 head-to-head trial (72 weeks, published in NEJM 2025), tirzepatide produced a greater average reduction than semaglutide 2.4mg. A question our prescribers hear most weeks is which injection gives better results, the honest answer is that head-to-head evidence favours tirzepatide, but suitability, tolerability and personal circumstances shape which medicine is right for any individual.

If you want to dig into how the trial numbers compare more directly, the most effective weight loss injection page sets them out side by side with full citations.

How tirzepatide and semaglutide are actually used day to day

Both injections follow a gradual dose escalation. Tirzepatide starts at 2.5 mg; the first pen's job is to help your system adjust rather than to drive significant weight loss straight away. Doses step up, typically every four weeks under prescriber review, through 5, 7.5, 10, 12.5 and 15 mg. Semaglutide (Wegovy) follows a similar principle: starting at 0.25 mg and moving through 0.5, 1.0, 1.7 and 2.4 mg, with the MHRA having approved a 7.2 mg maintenance dose in January 2026 for appropriate patients.

Both are injected subcutaneously, once a week, into the abdomen, thigh or upper arm, rotating sites each time. Neither requires special training to self-administer; the pre-filled pens are designed for home use. Storage is in the fridge at 2–8°C; for the exact room-temperature window allowed before using a pen, the Patient Information Leaflet is the reliable source, since this detail varies between products and lot sizes. The weight loss injection overview covers the practical steps of self-administering in more detail.

Side effects for both are predominantly gastrointestinal, nausea, loose stools, constipation and reflux are the most reported. These are usually most noticeable at the start of treatment or after a dose step, and they often ease within a couple of weeks. There is more to know beyond the GI effects, and the common side effects of weight loss injections page covers the full picture, including the urgent symptoms that always warrant same-day medical attention.

Who these injections are licensed for, and what that means in practice

The licensed starting point for both medicines is similar: adults with a BMI of 30 or above, or a BMI of 27 or above alongside at least one weight-related health condition such as high blood pressure, type 2 diabetes, high cholesterol or obstructive sleep apnoea. Lower BMI thresholds apply for some ethnic backgrounds under UK guidance. BMI alone does not confirm eligibility; a prescriber weighs the full clinical picture, including your medical history, current medicines and any contraindications.

Neither injection is recommended during pregnancy, while breastfeeding, or for anyone trying to conceive. They are not licensed for under-18s. Women taking oral contraceptive pills starting tirzepatide should discuss adding a non-oral method of contraception for the first four weeks of treatment and for four weeks after each dose increase, as absorption of the pill may be reduced, semaglutide does not carry the same evidence-based concern, though your prescriber should always be told about all your medicines. The NHS England guidance on weight-management injections covers these practical considerations in detail.

For a broader look at who qualifies under both the private and NHS routes, the guide to choosing between the two injections addresses suitability from a clinical standpoint, and safety considerations across the main options is worth reading before deciding.

Cost, access and the private route

Both tirzepatide and semaglutide are available privately through regulated online pharmacies and clinics, without the waiting times that affect NHS specialist pathways. NHS access exists (tirzepatide is recommended by NICE (TA1026) and semaglutide by NICE (TA875)) but each carries strict eligibility criteria and phased rollout timelines that mean many people who would benefit cannot currently access treatment through the NHS. Private treatment means paying for the medicine alongside a clinical assessment; a legitimate provider will always include the prescription and a clinical review in whatever they charge. The cost of weight loss injections in the UK page explains what typical private prices look like and what to watch out for in quotes that seem unusually low.

Sharps disposal is a practical point that often gets overlooked. Used pen needles must go into an approved sharps container, not household waste. A 1-litre sharps container is the standard size for home use. If you are thinking through what starting treatment actually involves, the free consultation at nume is reviewed the same day by a GPhC-registered prescriber (a real clinician, not a scoring algorithm) and is the right place to get personal answers about which injection suits your situation.