Wegovy 1 pen: what does your first injection actually involve?

What is a single Wegovy pen and how many doses does it hold?

This is the question our prescribers hear most often when someone opens the box for the first time. If you want to understand exactly how the device is built and functions, our guide to the Wegovy pen covers the mechanism in full, from the hidden needle to the dose-lock system. One Wegovy pen is a pre-filled, pre-set injection device, it holds four doses at a single strength, and each click delivers exactly one of those doses. There is no syringe to fill, no dose to calculate, and no setting to adjust. The pen does the measuring for you.

Novo Nordisk manufactures Wegovy in several pen strengths: 0.25 mg, 0.5 mg, 1.0 mg, 1.7 mg, and 2.4 mg, with the MHRA-approved 7.2 mg single-dose pen (approved April 2026) sitting at the top of the range. The strength printed on the box is the strength you inject every week for that month. Your prescriber decides which pen you start on and when, if ever, to move you up. That decision belongs with a clinician, not a protocol you follow yourself.

The NHS semaglutide medicines page confirms the weekly injection schedule and explains how semaglutide works: it mimics a gut hormone called GLP-1, slowing digestion and signalling fullness to the brain. Understanding the mechanism can make those first few weeks feel less mysterious.

When the fourth dose is done, a lock mechanism activates and the pen cannot be pressed again. Safe disposal matters at that point, a dedicated sharps container keeps used pens secure until your local pharmacy or council waste scheme can collect them.

Why does the first pen start at 0.25 mg rather than a higher strength?

The 0.25 mg starting dose exists to settle your system, not to treat your weight directly. Semaglutide slows gastric emptying, and starting at a higher strength would make nausea, vomiting, and diarrhoea far more likely, and far more disruptive. The low dose lets your digestive system adapt over four weeks before the next step.

This means most people notice little appetite change in week one. Some notice a mild shift by week three or four. Neither pattern is wrong. The STEP 1 trial, published in the New England Journal of Medicine, showed an average body-weight reduction of around 15% over 68 weeks at 2.4 mg, but that result was built across months of dose escalation, not from the first pen. Expecting dramatic results from the 0.25 mg pen sets an unfair benchmark.

The titration path typically runs every four weeks: 0.25 mg, then 0.5 mg, 1.0 mg, 1.7 mg, and finally 2.4 mg as the standard maintenance dose. Exact timing depends on how you tolerate each step, something your prescriber reviews before each dose change. If you are curious how the pen volume changes across strengths, the guide to Wegovy 1 ml pen details covers what the markings mean.

One thing worth doing before you open that first pen: store it in the fridge (2–8°C) from the moment it arrives. The SmPC specifies a limited window for keeping it at room temperature, and rather than quote a figure here it is always better to check the Patient Information Leaflet inside your box (or ask your prescriber) since getting storage right protects the medicine's effectiveness.

Where do you inject Wegovy and what does the process feel like?

Wegovy can be injected into three sites: the abdomen (at least a few centimetres from the navel), the front of the thigh, or the outer upper arm. Rotating between sites each week reduces the risk of skin irritation and fatty lumps forming at one spot. The guide to Wegovy injection sites goes into this in more detail if you are deciding which area suits you best.

The injection itself is brief. You remove the pen cap, press the tip firmly against the skin until you hear a click, hold for a count of ten, then release. The needle (very fine and short) is hidden inside the pen tip and retracts after use, so you never see it. Most people describe a mild pressure or brief sting. The alcohol wipe you use to clean the skin beforehand is a small step that matters; clean technique reduces infection risk at the site.

A detailed walkthrough of the full process, including cap removal and the post-injection check, is in the step-by-step Wegovy pen guide. The first time is almost always the most nerve-racking, it is worth reading that through the evening before your injection day, not five minutes before. Some people find Sunday morning works well, with a reminder set on the same day each week; others choose a weekday that fits around the school run or a predictable routine. Consistency matters because Wegovy's steady-state blood levels depend on injecting at roughly the same interval each week.

What side effects should you watch for during the first pen?

Gastrointestinal effects are the most common during the first four weeks: nausea is at the top of that list, followed by constipation, loose stools, indigestion, and burping. Most are mild and settle within the first week or two as your body adjusts. They are also more likely around injection day and the day after, then tend to ease.

Eating smaller, lower-fat meals and staying well hydrated helps. Heavy meals or rich foods soon after injection tend to make nausea worse. This is not a sign the medicine is failing, it is a sign it is working and your system is responding.

A small number of people experience more serious effects. Severe and persistent stomach pain that radiates toward the back (with or without vomiting) warrants urgent medical attention, as it can indicate acute pancreatitis, a known but infrequent risk that the MHRA highlighted in a January 2026 Drug Safety Update for GLP-1 medicines. Any allergic reaction, significant dizziness, or gallbladder symptoms should also be assessed promptly. If you ever want to report a suspected side effect, the MHRA Yellow Card scheme accepts reports directly from patients.

If you are comparing Wegovy with other weight-loss injection options, the guide to weight-loss injections and semaglutide explains how Ozempic differs from Wegovy and why the two are not interchangeable for weight management.

If the side effects feel difficult to manage, or you have questions about whether Wegovy is right for your situation, speaking directly with a prescriber is the right step. Speak to our prescribers for a free consultation, a real clinician reviews every case the same day.