Semaglutide 3ml pen: what arrives, what it contains and how it works

What does the 3ml Wegovy pen actually contain?

The Wegovy pen is a pre-filled, single-patient-use auto-injector. Inside the 3ml cartridge is a solution of semaglutide formulated for subcutaneous injection. The pen is pre-set to one fixed dose — you do not dial it or adjust it yourself — and each cartridge delivers four weekly injections. Once the final dose is given, the pen is spent and should be disposed of safely in a sharps container rather than a household bin.

Five pen strengths cover the full titration pathway: 0.25mg, 0.5mg, 1.0mg, 1.7mg and 2.4mg (with a 7.2mg option now approved by the MHRA for those who progress further). Each strength comes in its own clearly labelled pen, so moving up a dose means starting a new pen at the next level. If you want to understand the cartridge format in detail, our Wegovy 3ml pen page covers exactly what to expect from the device. The pen's covered needle extends automatically when pressed against the skin and retracts after injection, which most people find considerably less intimidating than it sounds. You can read more about the full range on the semaglutide pens overview.

When an order is dispatched through a regulated UK pharmacy, the pen travels in plain, unbranded packaging via DPD with a tracking link sent to your phone, so you know exactly when it will arrive, without anything on the box advertising what's inside.

How does the semaglutide inside the pen produce weight loss?

Semaglutide is a GLP-1 receptor agonist. GLP-1 is a hormone your gut releases naturally after a meal; it signals fullness to the brain, slows the rate at which the stomach empties and helps regulate blood sugar. Semaglutide mimics this signal but stays active far longer than the natural hormone, which is why a single weekly injection is sufficient. The result, for most people on an effective dose, is a meaningful reduction in appetite and calorie intake over time.

The STEP 1 trial, published in the New England Journal of Medicine, found an average body-weight reduction of around 15% over 68 weeks at the 2.4mg maintenance dose, alongside lifestyle changes. Those figures come from a controlled trial; individual results vary, and a prescriber is the right person to discuss realistic expectations for your situation. For a broader look at the injection and its licensed uses, the semaglutide injection page covers the clinical background in more detail.

It is worth being clear that Wegovy is licensed for weight management, while Ozempic (also semaglutide) is licensed for type 2 diabetes. They are not interchangeable for these purposes. The Ozempic and weight-loss injections page explains the distinction if you've come across both names.

Who can use the semaglutide 3ml pen for weight management?

The Wegovy pen is licensed for adults with a BMI of 30 or above, or for those with a BMI of 27 or above who also have at least one weight-related health condition, such as high blood pressure, raised cholesterol, obstructive sleep apnoea or type 2 diabetes. Lower BMI thresholds apply for some ethnic backgrounds under UK guidance. BMI alone does not guarantee approval; the prescriber considers your full medical picture, current medicines and any contraindications before issuing a prescription.

Wegovy is not recommended during pregnancy, whilst breastfeeding or if you are actively trying to conceive. It is not licensed for under-18s. People with a personal or family history of medullary thyroid carcinoma, or with multiple endocrine neoplasia type 2, should not use semaglutide. If you take an oral contraceptive pill, ask your prescriber whether additional contraception is advisable during treatment.

NICE recommends semaglutide (under guidance TA875) for use within specialist weight management services for up to two years, with strict eligibility thresholds. Private prescribing follows the licensed criteria in the SmPC rather than NICE's commissioning criteria, which is why the private route is accessible to people who do not meet the NHS's stricter qualification conditions or who prefer not to join a waiting list. The Wegovy overview sets out both routes clearly.

What should you know before your first injection?

Semaglutide is injected once a week, ideally on the same day each week. Suitable sites are the abdomen, thigh or upper arm; rotating the site each week reduces the chance of skin irritation at the injection point. The most common side effects are gastrointestinal: nausea, loose stools, constipation, reflux and reduced appetite. These tend to be most noticeable in the first few days after starting or after a dose increase, and for many people they ease off within a week or two as the body adjusts.

The NHS semaglutide medicines page lists side effects and when to seek urgent help. Severe or persistent stomach pain that radiates toward the back needs prompt medical attention, as it can be a sign of pancreatitis, an uncommon but serious reaction that the MHRA has highlighted in GLP-1 safety communications. Yellow Card at yellowcard.mhra.gov.uk is where you can report any suspected side effects.

For a step-by-step walkthrough of the injection process itself, the how to inject semaglutide guide is worth reading before your first dose. Storage is straightforward: keep the pen in the fridge between 2°C and 8°C until you need it. For the exact room-temperature window if you're travelling, always check the Patient Information Leaflet in the box rather than relying on general guidance, since that window has specific conditions attached.