Types of Weight Loss Injections: What's Available in the UK

Step 1: understand which injections are actually licensed for weight loss

This is where a lot of confusion starts, so it is worth being direct. In the UK, two injectable medicines are licensed specifically for weight management in adults: tirzepatide, sold as Mounjaro, and semaglutide, sold as Wegovy. That is the complete list. You may have heard of Ozempic or Saxenda, both are also injectable medicines in the same broad class, but Ozempic is licensed for type 2 diabetes and Saxenda for weight management at a higher dose of liraglutide; neither is the same product as Wegovy, and neither is what regulated weight-loss services prescribe when semaglutide for obesity is the topic. If you want to understand how weight loss injections work as a category, that page covers the mechanism in more detail.

The practical starting point is simple: if a seller is offering you a weight-loss injection without a prescription, that is a red flag, not a convenience. The NHS patient information on tirzepatide and the equivalent Wegovy page set out the clinical context clearly. Prescription-only status exists because these medicines carry real physiological effects and real contraindications.

Step 2: how each injection works, and why the mechanism matters

Wegovy is a GLP-1 receptor agonist. It mimics a gut hormone that signals fullness to the brain, slows gastric emptying, and damps down appetite. Mounjaro does the same thing but also activates a second receptor (GIP) which appears to reinforce the appetite-reduction effect through a slightly different pathway. That dual action is why Mounjaro is described as a dual GIP and GLP-1 agonist, and it is the only medicine of that kind licensed for weight loss in the UK at the moment.

In practical terms, both injections reduce how much you feel like eating; most people find portion sizes fall naturally rather than through willpower. The GI side-effect profile is similar for both: nausea, loose stools, constipation, indigestion and occasional reflux are common, particularly when the dose increases. These effects tend to settle within a week or two for most people, though not everyone. A common misconception is that the nausea means the medicine is harming you, in almost all cases it reflects the gut slowing down, which is the intended effect. It is uncomfortable, not dangerous, and it usually fades.

If you have type 2 diabetes and are considering a type 2 weight loss injection as part of your diabetes management, that page covers the overlap between the two licensed indications.

Step 3: dose schedules and what titration actually involves

Both injections are once-weekly subcutaneous injections, self-administered at home. Mounjaro comes in a pre-filled KwikPen at six UK strengths: 2.5, 5, 7.5, 10, 12.5 and 15 mg. Treatment starts at 2.5 mg (that first dose is there to let your system adjust, not to drive weight loss) and increases roughly every four weeks under prescriber supervision. Wegovy follows a similar pattern, moving from 0.25 mg up through 0.5, 1.0, 1.7 and 2.4 mg, with a 7.2 mg maintenance dose now also MHRA-approved for eligible adults.

The titration period matters more than most people expect. Both the clinical trial results and real-world outcomes reflect months of dose increases rather than the effect of a single pen. What that first injection actually involves is something our prescribers are asked about regularly. The injection site is typically the abdomen, thigh or upper arm, rotated weekly; both medicines require refrigerated storage between uses. Technique is straightforward and most people are confident within a couple of weeks.

Pricing context for private treatment is worth understanding too, for a clear picture of what different providers include in a quoted price, the weight-loss treatments page covers what is included at nume.

Step 4: eligibility, access routes and what comes next

Both medicines share a similar eligibility baseline: adults with a BMI of 30 or above, or 27 or above with at least one weight-related health condition such as high blood pressure, high cholesterol or obstructive sleep apnoea. Lower BMI thresholds apply for some ethnic backgrounds under UK clinical guidance. BMI alone does not determine approval, the prescriber assesses your full medical picture, including any medicines you already take and conditions that might affect suitability.

NHS access exists for both but through different routes and with strict, phased eligibility criteria that many people do not currently meet. Private treatment through a GPhC-registered pharmacy is the alternative. You can verify any online pharmacy's registration on the GPhC pharmacy register before sharing any personal information. Our own clinical and pharmacy team is registered under GPhC premises number 9012878.

If you are weighing up which injection might suit you, our guide to what type of weight loss injections are available goes deeper on the differences, and our overview of the types of weight loss injections is a useful place to start if you want a broader picture before comparing the two in detail. For a focused look at how the options break down, the page covering the 3 types of weight loss injections walks through each category side by side. And if you are ready to find out whether you are eligible, checking your eligibility with our prescribers is the straightforward next step, no commitment required at that stage.