The 2 weight-loss injections licensed in the UK

The misconception: that all weight-loss injections are basically the same medicine

This is the idea worth addressing first, because it genuinely shapes the decisions people make. Mounjaro and Wegovy both belong to a broader family sometimes called GLP-1 medicines, and both produce significant weight loss in clinical trials. From the outside they look similar: a pen, a weekly injection, a titration schedule. The assumption that follows is that they are interchangeable, or that whichever one is cheaper or more available is the right call.

They are meaningfully different medicines. Wegovy contains semaglutide, which activates the GLP-1 receptor — one gut-hormone pathway involved in appetite signalling and gastric emptying. Mounjaro contains tirzepatide, which activates both the GLP-1 and GIP receptors. The GIP pathway adds a second route through which the body regulates hunger and blood glucose. That dual action is why tirzepatide is often described as a different generation of treatment, not merely a stronger version of the same one. The NHS tirzepatide medicines page explains the mechanism in accessible terms if you want to read more.

Whether that distinction matters for any individual person is a clinical question. Body chemistry, existing conditions, other medicines and tolerance all play a part. That is precisely why a prescriber reviews the full picture rather than the patient picking a pen off a shelf.

What the two medicines share, and where they differ in practice

Both Mounjaro and Wegovy are once-weekly injections, self-administered into the abdomen, thigh or upper arm, with the site rotated each week. Both start at a low tolerability dose and are increased in steps over several months by the prescriber, not by the patient working through a fixed schedule independently. Both carry a Black Triangle (▼) designation in the UK, meaning the MHRA continues to collect additional safety data.

The differences in practice are real. Mounjaro's licensed strength range runs from 2.5mg up to 15mg across six dose steps. Wegovy's standard pathway tops out at 2.4mg weekly, though the MHRA approved a 7.2mg maintenance dose in early 2026, with a dedicated single-dose 7.2mg pen approved in April 2026 for adults with a BMI of 30 or above. The two titration schedules are different in length and in the specific time spent at each step, which is another reason mixing guidance from one medicine to the other is risky.

Side-effect profiles overlap considerably. Nausea, diarrhoea, constipation, indigestion and fatigue are common to both, most noticeable when starting or stepping up a dose, and typically settle over a couple of weeks. Anyone experiencing severe, persistent stomach pain that radiates to the back should seek urgent medical attention, that symptom pattern warrants prompt assessment, as the MHRA highlighted in its January 2026 Drug Safety Update on GLP-1 medicines. You can report any suspected side effect, or a suspect seller, via the Yellow Card reporting service.

For women taking oral contraceptives, tirzepatide in particular may reduce pill absorption during the first four weeks of treatment and for four weeks after each dose increase; adding a non-oral method during those windows is the current NHS recommendation. It is worth asking your prescriber about this if it applies to you, it is a quick conversation that many people overlook.

Who each injection is licensed for in the UK

Both medicines are licensed for adults managing their weight alongside a reduced-calorie diet and increased physical activity. The core licensing criterion is a BMI of 30 or above, or a BMI of 27 or above where at least one weight-related health condition is present, for example type 2 diabetes, high blood pressure, high cholesterol or obstructive sleep apnoea. Lower BMI thresholds apply for some ethnic backgrounds under UK guidance.

NICE has appraised both medicines for NHS use. Tirzepatide's appraisal (NICE TA1026) covers adults with a BMI of 35 or above plus at least one weight-related comorbidity, with NHS access being rolled out in phases. Wegovy's NICE appraisal (TA875) restricts NHS use to specialist weight management services for a maximum of two years. Neither set of NHS criteria applies to private prescribing, which follows the licensed indications and a full clinical assessment.

BMI alone never guarantees a prescription. Certain health histories (including a personal or family history of medullary thyroid carcinoma, or a history of pancreatitis) require careful prescriber review. Neither medicine is licensed for people under 18, during pregnancy, or while breastfeeding, or for anyone actively trying to conceive.

If you are trying to understand the broader landscape of options, a fuller overview of all weight-loss injections available in the UK may help put these two in context. There is also a general guide to weight-loss injections covering how the category works as a whole, and a separate page on newer injection options if you are curious about what has changed recently.

Getting either injection through a regulated service

Because Mounjaro and Wegovy are prescription-only medicines, the only legal route to either is a prescription issued after a clinical assessment. That can happen through your GP (subject to NHS eligibility criteria and local availability), through a specialist weight management service, or through a regulated online pharmacy. If you are still at the stage of researching your options, our page explaining what the weight-loss injections are covers the fundamentals in plain terms.

Any legitimate online service will ask you to complete a detailed health consultation, verify your identity and current weight, and have a qualified prescriber review your answers before issuing a prescription. If a seller offers either medicine without those steps (or without any prescription at all) that is a serious red flag. If you want to understand how Mounjaro and Wegovy sit alongside one another specifically, our page on what the 3 weight-loss injections are walks through each one in turn. The MHRA has warned publicly about counterfeit weight-loss pens sold through unofficial channels, some of which have contained insulin rather than the labelled medicine. Checking that a pharmacy is on the GPhC register at pharmacyregulation.org/registers takes under a minute and is the clearest way to confirm you are dealing with a legitimate registered pharmacy. For a broader look at the full range of options currently available, our page covering what weight-loss injections there are sets out the current landscape in one place.

At nume, a GPhC-registered Independent Prescriber reviews every consultation personally. You can read about the clinical team's approach on our prescriber profile page. If cost is a factor in your thinking, our treatment page sets out what is included in the price and how the process works from consultation to delivery. When you are ready, check your eligibility through a free consultation.