How Wegovy injections work — and what to expect week by week

Picture the moment you actually give yourself the first injection

You've collected your pen, picked a spot (most people start with the stomach, a couple of inches from the navel) and you're wondering what happens next. You uncap, press the pen against clean skin, and press the button. The pre-filled pen delivers a precise subcutaneous dose in a few seconds. There's no syringe to fill, no needle to attach for most pen formats. Done.

Beneath the skin, semaglutide is absorbed gradually into the bloodstream over the following days. This slow absorption is deliberate: it means a single injection maintains steady hormone levels across the whole week, rather than a sharp spike and drop. That steadiness is part of why the medicine only needs to be taken once. If you're curious about the mechanics behind the device, our guide to how a Wegovy pen works walks through each step in detail.

One thing worth keeping in mind: semaglutide takes time to build up. Most people notice changes in appetite within the first few weeks, but the full effect at a given dose settles in as the medicine reaches a steady state in your system. How quickly Wegovy starts working varies from person to person, and your prescriber can talk through what to watch for.

What semaglutide is actually doing inside your body

GLP-1 stands for glucagon-like peptide-1. Your gut releases it naturally when food arrives, and it does several things at once: it tells the brain you're satisfied, it slows gastric emptying so food lingers longer in the stomach, and it helps regulate blood sugar by signalling the pancreas. Semaglutide is a synthetic analogue of this hormone, modified so it stays active in the body far longer than the natural version, days rather than minutes.

That prolonged activity is what makes the weekly injection possible. It is also why appetite changes can feel quite different from ordinary hunger. Rather than craving a specific food, many people describe simply not thinking about food as often. Portions that would once have felt small become sufficient. This isn't willpower; it's the biology of the hormone system being recalibrated.

A question our prescribers hear most weeks is whether the injection itself hurts. For the vast majority of people, it doesn't, the needles used are short and fine, and the sensation is brief. Rotating your injection site each week helps keep the skin comfortable. If you'd like practical guidance on where on the leg is suitable, our page on injecting into the thigh covers technique and what to avoid.

Because GLP-1 medicines interact with gut motility, the most common early side effects are gastrointestinal (nausea, loose stools, or constipation) generally most noticeable after starting or moving to a higher dose, and often settling within a week or two. The NHS semaglutide page lists the full side-effect profile, including which symptoms warrant contacting a clinician promptly.

The dose schedule and why it matters

Wegovy doesn't begin at the dose shown on the clinical trial results. It starts low, at 0.25 mg, for the first four weeks. That's a tolerability step: the goal is to let your body adjust to slower gastric emptying before the dose goes up. Your prescriber then moves you through 0.5 mg, 1.0 mg and 1.7 mg, spending roughly a month at each level, before reaching the 2.4 mg maintenance dose. A higher 7.2 mg dose was approved by the MHRA in January 2026 for eligible patients with a BMI of 30 or above, reaching that threshold via a dedicated single-dose pen approved in April 2026.

Going faster than this schedule doesn't improve results, it mainly increases the chance of nausea. The titration exists because slower is genuinely better here. Your prescriber sets the pace based on how you're tolerating each step, and a clinical review happens before any repeat prescription is issued. That review matters: it's the checkpoint where dose changes are assessed properly.

Semaglutide is licensed in the UK for adults with a BMI of 30 or above, or 27 to 29.9 with at least one weight-related condition such as high blood pressure, high cholesterol or obstructive sleep apnoea. It is not licensed for use in pregnancy, while breastfeeding, or for anyone under 18. Details on the broader landscape of Wegovy injections in the UK including eligibility are covered on our treatment overview. It's also worth knowing that Ozempic is a different product, also semaglutide, but licensed for type 2 diabetes, not weight management.

What clinical trials showed, and what that means for you

The headline figure most people have seen comes from the STEP 1 trial, a 68-week study of semaglutide 2.4 mg in adults with obesity, published in the New England Journal of Medicine. Participants lost an average of around 15% of their body weight. In trials of the newer 7.2 mg dose, that average rose to around 20.7% over 72 weeks, closing the gap with the results seen from tirzepatide in the SURMOUNT programme.

These are averages. Some people respond more, some less. The trials were also conducted alongside dietary changes and increased physical activity, the medicine works as part of a broader approach, not as a standalone fix. That context matters for setting realistic expectations. If you're weighing up options, our weight-loss treatment overview covers how different medicines compare.

Whether Wegovy is clinically appropriate for you depends on your full medical history, conditions, medicines you already take, and other factors that a prescriber needs to assess. If you'd like that assessment without a waiting list, starting a free consultation with our prescribers is the next step.