Injectable Semaglutide: How It Works, What to Expect, and Who It Suits

Step 1 — Understanding what the pen actually does inside your body

Semaglutide mimics a hormone called GLP-1, which the gut releases naturally after eating. By binding to GLP-1 receptors in the brain's appetite centres and in the stomach wall, it reduces hunger signals and slows the pace at which food leaves the stomach. The result is that smaller meals feel more satisfying, and the urge to snack between them diminishes for most people.

It is a single-pathway mechanism (GLP-1 only) which distinguishes it from tirzepatide, the active ingredient in Mounjaro, which also targets GIP receptors. That distinction matters for understanding the clinical evidence, but which medicine suits you is a question a prescriber works through with your full health picture, not a self-selection exercise.

NICE recommended Wegovy for weight management in its technology appraisal TA875 for eligible adults, and the clinical trial data behind that recommendation (the STEP programme) reported an average weight reduction of around 15% over 68 weeks at the 2.4 mg maintenance dose. Real-world results vary; the trial figures are a reference point, not a promise. You can read more about the semaglutide injection in detail, including how the STEP evidence translates into UK licensing.

Step 2, The titration schedule and what arrives when you start

The licensed starting dose is 0.25 mg weekly. That figure surprises some people, it is not a therapeutic dose in the weight-loss sense; its job is to let your body adapt to the medicine gradually, reducing early nausea. From there, the schedule moves through 0.5 mg, 1.0 mg, and 1.7 mg, with a minimum of roughly four weeks at each level, before reaching the standard 2.4 mg maintenance dose.

In January 2026, the MHRA also approved a 7.2 mg maintenance dose, initially as three 2.4 mg pens used weekly, followed by approval in April 2026 of a dedicated single-dose 7.2 mg pen. Trials reported approximately 20.7% average weight loss over 72 weeks at this higher dose. Whether a particular dose or pen format is available to you is confirmed at consultation; never assume stock or format before a prescriber has reviewed your case.

When your first order is dispatched from the GPhC-registered pharmacy, it travels with DPD in a plain, unbranded refrigerated box, no clinic name on the outside, a tracking link on your phone, and the pen itself sealed inside with clear patient information. Storage is straightforward: refrigerated at 2–8°C, with a limited room-temperature window detailed in the Patient Information Leaflet. Always follow the leaflet, not memory.

Step 3, Giving the injection and building the habit

Each Wegovy injectable pen is pre-filled and pre-set to the correct dose, so there is no need to dial a number or draw up liquid. The injection goes into the fatty tissue just under the skin at the abdomen, thigh, or upper arm. Rotating sites each week helps avoid localised skin reactions.

For step-by-step injection technique, the practical guide to injecting semaglutide walks through preparation, site selection, and what to do if a dose is missed, though missed doses and any timing questions should always be confirmed with your prescriber or the leaflet rather than acted on from memory. Alcohol swabs for cleaning the injection site and a proper sharps container for used needles are worth having to hand from the start; a 1-litre sharps container is available directly from our pharmacy.

The habit itself tends to settle quickly. Most people find a fixed day of the week works best (a Sunday evening or a Monday morning, whichever fits around food timing) and within a few weeks it becomes routine rather than an event.

Step 4, Side effects to watch for, and when to get medical help

The most common side effects are gastrointestinal: nausea, vomiting, diarrhoea, constipation, and indigestion. They are typically worst in the first week or two after starting or after moving up a dose step, and they ease for most people as the body adjusts. Eating smaller portions, avoiding fatty meals, and staying hydrated all help.

More serious but less common effects include gallbladder problems and pancreatitis. In January 2026 the MHRA highlighted acute pancreatitis as a known, infrequent but potentially serious effect of GLP-1 medicines: if you develop severe stomach pain that spreads to your back (with or without vomiting) seek urgent medical help rather than waiting to see if it passes. You can report any suspected side effect, including from injectable semaglutide, via the MHRA Yellow Card scheme.

This medicine is not recommended during pregnancy, while breastfeeding, or for people actively trying to conceive. Women taking oral contraceptives should discuss contraception options with their prescriber before starting, as GLP-1 medicines can affect how the pill is absorbed. Under-18s are not a licensed group. These are not edge cases, they are part of the clinical assessment every prescriber at nume carries out before treatment is approved. If any of this applies to you, your consultation is the right place to raise it. You can also explore the range of semaglutide injection options available to adults in the UK before deciding whether to proceed.

For a broader look at the weight-loss medicines available through a regulated UK pharmacy, the weight-loss treatment overview sets out your options clearly. And if cost is a factor in your thinking, the Wegovy cost context page explains honestly what legitimate private treatment involves, including which semaglutide pen formats are currently available and how their pricing compares, and what the market actually looks like in 2025 and 2026.