Wegovy contents: what the pen contains and how it works

Step 1: the active ingredient, semaglutide and what it actually is

Semaglutide is a synthetic analogue of glucagon-like peptide-1 (GLP-1), a hormone the gut releases after eating. Natural GLP-1 lasts only a couple of minutes before enzymes break it down; semaglutide is engineered to resist that breakdown, remaining active in the body for roughly a week. That extended half-life is what makes a once-weekly injection workable. Inside the pen, semaglutide is dissolved in a sterile aqueous solution at concentrations that match each dose step in the licensed titration schedule: 0.25 mg, 0.5 mg, 1.0 mg, 1.7 mg and 2.4 mg, with the newer 7.2 mg strength following the same principle at a higher concentration. The Wegovy treatment page explains how those dose steps are used across the titration pathway.

Once injected into the subcutaneous tissue (typically the abdomen, thigh or upper arm), semaglutide is absorbed into the bloodstream and travels to GLP-1 receptors in the hypothalamus, gut and elsewhere. The effect is a reduction in appetite signalling and a slower rate of gastric emptying, meaning food leaves the stomach more gradually, which extends the feeling of fullness. According to NHS guidance on semaglutide, these combined actions are what underlie Wegovy's licensed use in weight management.

The STEP 1 trial, published in the New England Journal of Medicine, reported an average body-weight reduction of around 15% over 68 weeks at the 2.4 mg maintenance dose alongside lifestyle changes. The more recently approved 7.2 mg strength produced approximately 20.7% average loss in its supporting trial, approaching results seen with tirzepatide. Those are trial averages; individual outcomes vary and depend on a range of factors the prescriber discusses at assessment.

Step 2: the inactive excipients and why they matter

The other constituents in a Wegovy pen are present in small amounts but each serves a specific role. Disodium phosphate dihydrate acts as a buffer, keeping the pH of the solution stable so the semaglutide remains chemically intact. Propylene glycol helps solubility and contributes to the stability of the formulation. Phenol is the preservative, it prevents microbial contamination across the multiple weekly doses delivered from one pen. Water for injections makes up the remainder of the solution.

For most people these excipients present no issue. If you have a known sensitivity to phenol or propylene glycol, that is worth raising explicitly during your consultation. Full excipient detail for the specific strength and batch you receive will always appear in the Patient Information Leaflet inside your pack; the Mounjaro and Wegovy SmPCs on the eMC publish the authorised product information for prescribers and pharmacists, and you can read the Wegovy entry there directly. The excipient list does not change across dose strengths, only the semaglutide concentration itself differs.

One thing worth knowing: if you are curious about what Wegovy contains, it includes no gluten, lactose or animal-derived gelatine in its injectable formulation, though the Patient Information Leaflet is always the definitive source for your specific pen. The Wegovy ingredients page covers the individual components in more depth.

Step 3: the pen itself, what you're actually handling

The Wegovy auto-injector pen is a single-use, pre-filled device with a built-in, covered needle. You do not attach or see the needle directly; it deploys and retracts automatically when you press the pen against the skin. Each pen contains four 0.5 ml doses delivered once a week at the same day and approximate time each week. The pen has a dose counter so you can track how many injections remain.

Storage matters for keeping the contents effective. Wegovy pens should be kept refrigerated between 2°C and 8°C until the expiry date printed on the label. Once you start a pen, it can be kept at room temperature (below 30°C, away from heat sources and direct light) for up to six weeks. A practical habit many patients develop is keeping the current pen in the fridge door, separate from the spares stacked at the back, so the in-use one is always easy to find. Never freeze a pen; freezing damages the semaglutide and the device. Always check the solution is clear and colourless before injecting, discard it and contact your prescriber if it looks cloudy or contains visible particles.

If you are comparing the injectable pen with the newer oral option, the Wegovy components page sets out how the tablet formulation differs, including the absorption enhancer SNAC that allows semaglutide to pass through the gut wall when taken by mouth.

How this relates to what you'll be prescribed

Wegovy is a prescription-only medicine. The contents of the pen are identical regardless of where it is legitimately dispensed in the UK, because the product must meet the same MHRA-authorised specification. What varies between providers is the clinical process: the depth of the assessment, whether a real prescriber reads your answers or automated software flags them, and what aftercare follows.

At nume, a GPhC-registered Independent Prescriber personally reviews every consultation, the same day it's submitted. There are no subscriptions and no auto-renewals; each repeat order is reviewed again before anything is dispensed. If you want to understand the cost side before starting, the Wegovy cost page explains what private treatment typically involves. To check whether Wegovy might be suitable for you, the starting point is a free clinical assessment. Our weight-loss treatment overview explains how the process works from beginning to end.