The 3 types of weight loss injections licensed in the UK

What is tirzepatide (Mounjaro), and why is it different from the others?

Tirzepatide is the active ingredient in Mounjaro, made by Eli Lilly. It is the only injection in this group to activate two gut-hormone receptors: GIP and GLP-1. Both pathways are involved in regulating appetite and blood-sugar levels. By pressing both simultaneously, tirzepatide tends to produce a stronger and more sustained reduction in hunger than medicines that act on just one receptor.

In SURMOUNT-1, a 72-week clinical trial published in the New England Journal of Medicine, participants using 15mg tirzepatide lost an average of around 20–21% of their body weight alongside lifestyle changes. That figure was notably higher than anything seen in equivalent semaglutide trials, and was broadly confirmed in the SURMOUNT-5 head-to-head comparison in 2025.

Mounjaro is a once-weekly subcutaneous injection via a pre-filled KwikPen. Treatment starts at 2.5mg (a dose whose job is to let the body adjust gradually rather than to drive weight loss) and is stepped up by the prescriber over several months. It is licensed for adults with a BMI of 30 or above, or 27 or above with at least one weight-related condition such as high blood pressure, high cholesterol, or type 2 diabetes, which has its own considerations when it comes to choosing a weight loss injection.

Mounjaro carries a Black Triangle (▼) in the UK, meaning the MHRA collects additional safety data on it. The NHS patient information for tirzepatide is a reliable reference for side effects and storage requirements. Keep your pen in the fridge door — it needs to stay between 2°C and 8°C until the day you use it.

What is semaglutide (Wegovy), and how does the injection version work?

Semaglutide is the active ingredient in Wegovy, made by Novo Nordisk. It is a GLP-1 receptor agonist, meaning it mimics the gut hormone GLP-1 to reduce appetite, slow gastric emptying, and increase the feeling of fullness after eating. It acts on one receptor pathway rather than two.

The STEP 1 trial (68 weeks, adults with obesity, no diabetes) found an average body-weight reduction of around 15% at the 2.4mg weekly maintenance dose. A higher dose (7.2mg) received MHRA approval in early 2026, with trial data showing average losses approaching 20.7% over 72 weeks. Whether a specific pen format or dose is available is something confirmed at the point of clinical assessment, not assumed in advance.

Wegovy is also a once-weekly subcutaneous injection. The titration schedule runs from 0.25mg up through several steps to 2.4mg (and now 7.2mg for eligible patients), with each step typically lasting around four weeks. It is licensed for adults with a BMI of 30 or above, or 27 or above with a weight-related health condition. NICE recommends semaglutide under TA875 within specialist NHS weight management services for a maximum of two years; private routes exist for those who don't meet the NHS referral threshold or prefer not to wait.

Wegovy also holds separate UK authorisations for cardiovascular risk reduction and (from July 2026) a form of fatty liver disease called MASH. For weight management purposes, the licensing criteria are the same as described above.

What is liraglutide (Saxenda), and does it still have a place?

Liraglutide is the active ingredient in Saxenda, also made by Novo Nordisk. Like semaglutide, it is a GLP-1 receptor agonist. Unlike the other two, it requires a daily injection rather than a weekly one, a practical difference that matters for some people.

Average weight loss in clinical trials was around 5–8% of body weight, which is meaningfully lower than the figures seen with either of the two newer medicines. Liraglutide was the first GLP-1 injection licensed for weight management in the UK, and its safety profile is well established over a longer period of post-market use.

Saxenda is licensed for adults with a BMI of 30 or above, or 27 or above with a weight-related condition. It is not dispensed by nume. Pages covering the full range of injection options discuss liraglutide in more detail for those weighing it against the newer alternatives.

For most adults starting weight-management treatment in 2025 or 2026, the clinical conversation has largely moved to tirzepatide and semaglutide, given the larger average weight losses and the once-weekly convenience. That said, which medicine (if any) is appropriate is a decision made with a prescriber based on your full medical picture, not a comparison table.

Do I need a prescription, and how is the right injection chosen?

Yes. All three injection types are prescription-only medicines under UK law. No legitimate pharmacy can dispense them without a valid prescription issued following a clinical assessment. If you are unsure what types of weight loss injections are available and which might suit your situation, that is a good place to start before speaking to a prescriber. If a seller is offering weight loss injections without that process, that is a red flag the MHRA has warned about explicitly, fake pens have been found in the UK supply chain, and some have caused serious harm.

The right injection is chosen by weighing your BMI, relevant health conditions, any medicines you already take, and your preferences around injection frequency and expected results. A GPhC-registered prescriber does that assessment. At nume, the clinical team reviews consultations the same day, a real clinician reads your answers, not software. If you have a condition such as hypothyroidism, that is exactly the kind of detail the prescriber needs before a medicine decision is made.

The free consultation at nume covers the full eligibility picture and, if treatment is clinically appropriate, includes the prescription, delivery, and ongoing clinical support. There are no hidden fees and no subscription. If you want to understand the cost side before taking that step, the weight loss treatment overview sets out what is included in a single transparent price.