What the semaglutide injection is used for — and what it isn't

The myth that Wegovy and Ozempic are the same product for the same purpose

This is where most of the confusion starts. Both Wegovy and Ozempic contain semaglutide, manufactured by Novo Nordisk. But the semaglutide injections available in the UK carry different licences, different maintenance doses and entirely different intended uses.

Ozempic is licensed for type 2 diabetes management. Wegovy is licensed for weight management. Using one instead of the other is not a clinical workaround, it is prescribing for an unlicensed indication, which requires clinical justification and falls outside standard practice. If you are researching Ozempic for weight loss, the honest answer is that it is not the medicine licensed for that purpose in the UK. Wegovy is.

The NHS is clear on this distinction, and the MHRA has separately confirmed that GLP-1 medicines are not assessed or approved for quick or cosmetic weight loss. The semaglutide injection used for weight management is specifically the 2.4mg maintenance dose in the Wegovy formulation, following a graduated titration schedule set by your prescriber.

What Wegovy is actually licensed to treat, and the eligibility criteria that follow

Wegovy's UK licence covers adults with a BMI of 30 or above, or 27 to 29.9 alongside at least one weight-related health condition. Conditions that may qualify alongside a lower BMI include prediabetes, hypertension, high cholesterol, obstructive sleep apnoea and type 2 diabetes itself. Lower BMI thresholds can apply for certain ethnic backgrounds under UK clinical guidance.

Semaglutide has also received MHRA approval for reducing the risk of major cardiovascular events in eligible adults, and in July 2026 it gained a further conditional approval for a form of fatty liver disease known as MASH. For the purposes of weight management, though, the relevant licence remains the one covering BMI-based eligibility with lifestyle changes alongside treatment.

A quick check that takes under a minute: the NHS BMI calculator will tell you your current BMI and give you a reference point before you speak to a prescriber. It is not a substitute for a clinical assessment, but it orients the conversation.

Eligibility is never just a BMI number. A prescriber looks at the full picture, existing conditions, medications, contraindications and treatment history. For more on who qualifies and how the process works, the Wegovy overview page covers the clinical criteria in detail.

How the semaglutide injection works, the mechanism behind the weight loss

Semaglutide is a GLP-1 receptor agonist. GLP-1 (glucagon-like peptide-1) is a hormone your gut produces naturally after eating. It tells your brain you are full, prompts insulin release and slows gastric emptying, the rate at which food moves from your stomach into the small intestine.

The injectable form mimics and extends this effect. Appetite signals become more muted between meals. Food takes longer to move through the upper digestive system, so fullness arrives sooner and lasts longer. Over weeks and months, most people find their overall calorie intake falls without effortful restriction, the hunger simply eases.

The STEP 1 trial, published in the New England Journal of Medicine, ran for 68 weeks and included adults with obesity who did not have diabetes. Participants using semaglutide 2.4mg achieved an average body-weight reduction of around 15%, compared with around 2.4% in the placebo group, alongside lifestyle support. That is a meaningful clinical result, and it is also a trial average. Individual outcomes vary.

Wegovy is a Black Triangle medicine, meaning it carries additional MHRA monitoring while post-marketing safety data continues to accumulate. The semaglutide injection page has a fuller breakdown of what that designation means in practice.

Practical realities: injection sites, storage and what this treatment involves day-to-day

Wegovy is administered once weekly as a subcutaneous injection, into the fatty tissue beneath the skin, not into muscle. The three licensed sites are the abdomen, the thigh and the upper arm. Rotating between sites each week reduces the chance of localised skin changes. There is practical guidance on choosing and rotating your injection site if that is unfamiliar territory.

Storage matters. Wegovy pens must be kept refrigerated at 2 to 8°C until you are ready to use them. There is a limited window during which a pen can be kept at room temperature, and the exact timeframe is specified in the Patient Information Leaflet, it varies, so the leaflet is the right source rather than any general rule. A common question is whether Wegovy must always stay in the fridge; the short answer is yes, until you need it.

Side effects are mostly gastrointestinal, particularly in the first weeks of treatment or after a dose increase: nausea, loose stools, constipation and indigestion are the most frequently reported. They typically settle as your body adjusts. If you notice a small bump or bubble under the skin after injecting, that is usually an injection-technique issue rather than a cause for concern, though a prescriber can advise.

Semaglutide is not recommended during pregnancy, while breastfeeding, or if you are actively trying to conceive. It is not licensed for anyone under 18. These are firm clinical boundaries, not caveats. The NHS semaglutide medicines page lists the full set of contraindications and interactions worth reviewing before you speak to a prescriber.

If you are considering private treatment and want to understand the cost side of things, our guide to where Wegovy can be obtained in the UK covers the private route alongside NHS access. For a broader look at all prescription weight-loss options, the treatment overview sets out how each one compares.