The weight loss injection Wegovy: what it actually does

You've picked up your first pen — what happens from here

Picture this: your Wegovy pen has arrived, it has been in the fridge overnight, and you are about to use it for the first time. The device is pre-filled and pre-set, so there is no cartridge to load or dose to dial. You choose an injection site (stomach, outer thigh or upper arm are all fine) wipe the skin, press the pen against it, and press the button. The pen drives the needle in and delivers the dose automatically. Most people say they barely feel it.

What you are injecting at that first stage is 0.25mg of semaglutide. That starting dose is a tolerance dose, not the one doing the heavy lifting on weight; its job is to let your body adjust to the medicine so that side effects, particularly nausea, stay manageable. Your prescriber steps this up in roughly four-weekly increments: 0.25mg, then 0.5mg, 1mg, 1.7mg, and finally 2.4mg, which is the standard maintenance dose. A higher 7.2mg maintenance dose was approved by the MHRA in January 2026, and a dedicated single-dose pen for it followed in April 2026, though specific dose availability at any given time is confirmed at consultation, not before.

Rotating your injection site each week matters practically, not just theoretically. Using the same spot repeatedly can cause small lumps under the skin that slow absorption. Plenty of detail on the pen device itself, including how to handle a missed dose, lives in our guide to the Wegovy pre-filled pen, and the Patient Information Leaflet that comes in the box is the definitive reference for storage and technique questions.

What semaglutide is doing while you go about your week

Semaglutide belongs to a class of medicines called GLP-1 receptor agonists. GLP-1 is a hormone your gut releases after eating; it signals the brain to reduce appetite, slows how quickly the stomach empties, and helps regulate blood sugar. Semaglutide mimics that signal on a longer, sustained basis, which is why appetite reduction tends to set in and stay rather than spike and fade.

In the STEP 1 trial, published in the New England Journal of Medicine, 68 weeks of 2.4mg semaglutide alongside lifestyle changes produced an average weight loss of around 15% in adults with obesity and no diabetes. That is a population average, some people lose more, some less, and no individual result is guaranteed. The medicine works best alongside changes to diet and activity, which is why every licensed programme includes that element.

People often ask whether the injection hurts. Most find the needle so fine they feel almost nothing. What catches people more off guard is the appetite shift in the first few weeks: food that used to feel essential becomes easier to leave. That is the medicine working, but it can also mean protein and hydration need a bit more attention when portions shrink, something worth raising with your prescriber or a dietitian.

For a fuller look at how semaglutide compares with similar injections, our semaglutide weight-loss injection overview covers the mechanism in more depth.

Who the Wegovy injection is licensed for, and who should not use it

The UK licence covers adults with a BMI of 30 or above, or a BMI of 27 or above alongside at least one weight-related condition such as high blood pressure, raised cholesterol, type 2 diabetes or obstructive sleep apnoea. Lower BMI thresholds apply for people from South Asian, Chinese, Middle Eastern, Black African or African-Caribbean backgrounds under UK guidance. A BMI that clears those numbers is not enough on its own; the prescriber reviews your full medical picture, including any medicines you take and conditions you have.

Wegovy is not recommended during pregnancy, while breastfeeding, or if you are actively trying to conceive. It is not licensed for under-18s. A history of pancreatitis, medullary thyroid carcinoma or MEN2 syndrome requires specific discussion. Women using the oral contraceptive pill should be aware that the injection can slow absorption of other oral medicines in the early weeks; the NHS England guidance on weight-management injections covers the contraception interaction clearly and is worth reading before you start.

If any side effect feels serious (severe stomach pain that spreads to your back, signs of an allergic reaction, or significant dehydration from persistent vomiting) seek medical attention promptly rather than waiting for your next review. You can also report any suspected side effect through the MHRA's Yellow Card scheme.

Getting the Wegovy injection through a regulated UK pharmacy

Wegovy is a prescription-only medicine. The only lawful route to it is a prescription issued by a registered prescriber following a proper clinical assessment. That assessment cannot happen on a form you fill in at 2am with no follow-up; it has to be a genuine clinical review of your health, your history and your goals.

At nume, every consultation is personally read by a GPhC-registered Independent Prescriber on the day it is submitted. Order before midday on a working day and, once clinically approved, your treatment is dispatched the same afternoon and delivered free the next working day by DPD in plain unbranded packaging, practical for people who need to pick it up before the school run and do not want to explain a labelled box. The cost question (what private treatment realistically involves and what is included) is covered on our Wegovy cost page.

You can verify any online pharmacy on the GPhC register at pharmacyregulation.org, our registration number is 9012878. Any seller offering Wegovy weight loss injections or semaglutide without asking for a prescription is operating outside the law, and fake pens have been seized in significant numbers across the UK. The MHRA has flagged this publicly and the risk is real.

If you would like a prescriber to assess whether the Wegovy injection is appropriate for you, speak to our prescribers, the consultation is free and there is no obligation to proceed.