Wegovy 4 Pens Explained: One Box, Four Weekly Doses

What the trial evidence tells us about the once-weekly schedule

The once-weekly injection timing that gives Wegovy its four-pens-per-box structure was central to how it was tested and approved. In the STEP 1 trial, adults with obesity injected semaglutide once weekly over 68 weeks, with the dose gradually increased by their clinical team. Average weight loss reached around 15% of body weight at 2.4 mg maintenance dose. That steady, week-by-week rhythm matters: semaglutide builds up gradually in the body, which is partly why tolerability improves over time rather than hitting its ceiling on the first pen.

The NHS semaglutide medicines page confirms the once-weekly injection timing and explains that missing a dose by more than five days means skipping that dose entirely rather than doubling up. If you want to understand the broader range of semaglutide pens available and how they compare, that context can be useful when discussing options with your prescriber. The four-pen box is sized to match this rhythm cleanly: one box, one calendar month, one strength.

A quick habit worth adopting when a new box arrives: before you store it, check that the strength printed on the label matches what your prescriber has confirmed for this stage. It takes about thirty seconds and catches any dispensing confusion early.

Why the box strength changes as your dose increases

Titration is built into the Wegovy programme by design. Treatment begins at 0.25 mg weekly, a starting dose chosen to let your body adjust before the therapeutic doses come later. The full pathway moves through 0.5 mg, 1.0 mg, 1.7 mg and 2.4 mg, with roughly four weeks at each level. Because each pen is factory-set to its dose, a 0.25 mg pen cannot deliver 1.0 mg. The strength must physically change, which means the box changes at each new stage.

This is worth understanding because it explains why you need a fresh prescription review rather than simply reordering the same box. At nume, a prescriber reviews every repeat order (checking your progress, any side effects and whether the next dose step is appropriate) before a new box is dispensed. You can read more about how Wegovy pens are structured across the full course if you want a clearer picture of what each stage looks like.

If you are curious about how Wegovy pens work and what happens inside the device when you inject, that page gives a full explanation of the mechanism alongside the practicalities of each dose. Correct technique reduces the chance of a failed injection, which matters more than it might seem when each pen counts.

Side effects across a four-week box and what to watch for

Gastrointestinal effects (nausea most commonly, along with loose stools, constipation and indigestion) are most noticeable in the first week or two after starting a new strength. That timing overlaps almost exactly with the early pens in a new box, which can feel dispiriting if you are not expecting it. Most people find the discomfort settles considerably by pens three and four as the body adjusts.

A more serious but infrequent risk is pancreatitis. In January 2026 the MHRA issued a Drug Safety Update highlighting acute pancreatitis across GLP-1 medicines: if you develop severe stomach pain that spreads to your back, with or without vomiting, stop the injection and get urgent medical help rather than waiting to see if it passes. You can report any suspected side effects through the MHRA Yellow Card scheme.

Injection-site reactions (mild redness or tenderness) are common and usually brief. Rotating between the abdomen, thigh and upper arm with each weekly injection reduces cumulative irritation. If you want a thorough walkthrough of technique, the injection guide covers site rotation clearly.

Prescription, storage and what happens between boxes

Wegovy is a prescription-only medicine. A box of four pens cannot be dispensed legally without a prescription issued following a clinical assessment. That means each time you move to the next dose strength, your prescriber needs to authorise it, a clinical check, not a formality.

Keeping the pens refrigerated until use protects their potency. An unused pen that has been left at room temperature for longer than the leaflet permits should not be injected. Check the patient information leaflet that comes in the box for the exact window; never rely on a figure you have read elsewhere.

If you are exploring the cost of a private Wegovy prescription, the cost context page explains what legitimate private pricing typically covers. And if you are weighing up whether semaglutide or another option suits your situation, the treatment overview sets out what is available and how each approach differs. When you are ready to speak to a prescriber about whether Wegovy is right for you, starting a free consultation with our clinical team takes a few minutes and is reviewed by a GPhC-registered prescriber the same day.