3ml Semaglutide Pens: What the Volume Tells You (and What It Doesn't)

Why does the pen say 3ml if the dose is measured in milligrams?

This is one of the questions our prescribers field most weeks, and it's a fair one. The 3ml figure refers to the total volume of liquid inside the Wegovy pen, the physical amount of solution in the cartridge. The milligram figure (0.25mg, 0.5mg, 1.0mg, 1.7mg, or 2.4mg) describes the amount of semaglutide dissolved in that liquid at each weekly injection point.

Think of it like a bottle of medicine where the bottle size and the dose are two different things. A higher dose of Wegovy doesn't mean more liquid per injection; it means a higher concentration of the active ingredient in the same volume. The pen mechanism is calibrated to deliver precisely the right amount at the right strength, which is why Wegovy pens are not interchangeable between dose strengths, each pen is manufactured for a specific step on the prescribing ladder.

The NHS medicines page for semaglutide sets out the dose steps and what each is used for, and is the clearest plain-English summary of how this medicine works in practice. If you are ever unsure which pen you have been dispensed, the dose strength is printed clearly on the outer carton and on the pen itself, check both before injecting.

What does the 3ml pen actually contain, and how long does it last?

At the standard once-weekly dosing schedule, a single 3ml Wegovy pen is designed to provide four weekly injections, making it a roughly four-week supply at each dose step, which aligns with the titration intervals your prescriber will follow. The prescribing schedule begins at 0.25mg for the first four weeks (a starting point chosen to let your system adjust, not to produce weight loss) and steps upward through 0.5mg, 1.0mg, 1.7mg and then 2.4mg, spending a minimum of four weeks at each level.

In January 2026 the MHRA also approved a 7.2mg maintenance dose, initially delivered via three 2.4mg pens weekly and subsequently as a dedicated single-dose pen approved in April 2026. This higher-strength option uses the same semaglutide molecule but at a concentration not available in the standard 3ml pen format. If you are curious about which pen formats are currently dispensed, that is best confirmed at consultation, availability is clinically reviewed on a case-by-case basis.

Storage matters here too. Wegovy pens should be kept in the fridge between 2°C and 8°C, many people keep the current pen on the fridge door for easy access, which works well. Once you have started a pen, there is a limited window for room-temperature storage; always follow the instructions in your Patient Information Leaflet for the exact timeframe, since that is the verified guidance for your specific pen.

Who is a 3ml semaglutide pen prescribed for under UK licensing?

Wegovy (semaglutide) is licensed in the UK for weight management in adults. The two thresholds are a BMI of 30 or above, or a BMI between 27 and 29.9 alongside at least one weight-related condition, which might include type 2 diabetes, high blood pressure, high cholesterol, or obstructive sleep apnoea. Lower BMI thresholds apply for some ethnic backgrounds under UK guidance, reflecting differences in cardiometabolic risk. The prescriber reviews the full clinical picture, not just the BMI figure alone.

NICE recommends semaglutide (TA875) for use within specialist weight management services for a maximum of two years, at BMI thresholds of 35 or above with at least one comorbidity, as part of a multidisciplinary programme. You can read the full recommendation on the NICE semaglutide appraisal page. Private prescribing follows the licensed indications in the SmPC rather than the NICE commissioning criteria, which is why private routes are accessible to people who do not qualify for NHS treatment or who are unwilling to wait.

Wegovy is not suitable during pregnancy, while breastfeeding, or for anyone trying to conceive, and it is not licensed for anyone under 18. Certain conditions (including a personal or family history of medullary thyroid carcinoma) require careful prescriber assessment before treatment can be considered. A thorough consultation is not a formality; it is the mechanism that keeps treatment safe. You can read more about how we approach eligibility on our Wegovy contraindications page.

What side effects are associated with semaglutide, and when should you seek help?

The most commonly reported side effects with semaglutide are gastrointestinal: nausea, vomiting, diarrhoea, constipation, and reflux appear most often in the first weeks of treatment or after a dose increase, and tend to settle as the body adjusts. Fatigue, headache, dizziness, and injection-site reactions are also reported. These are not trivial, but for most people they are manageable and time-limited.

There are symptoms that require prompt medical attention. Severe stomach pain that spreads to your back (particularly if it comes with vomiting and does not ease off) may indicate pancreatitis, a serious but uncommon complication. The MHRA highlighted this in a Drug Safety Update for GLP-1 medicines in early 2026 and advises anyone experiencing these symptoms to seek urgent help. Signs of a serious allergic reaction (swelling, difficulty breathing, rapid heartbeat) also warrant emergency care.

If you experience symptoms you are unsure about during treatment with a pen dispensed through nume, our prescribers are available for aftercare seven days a week. You can reach the team via the contact page. Suspected side effects from any medicine can also be reported directly to the MHRA via the Yellow Card scheme, and doing so helps build the safety evidence base for everyone on these medicines.

For a broader look at how semaglutide compares with other licensed weight-loss medicines (and how to think about which option suits your situation) our semaglutide overview covers the full picture. And if cost is part of your thinking, our Wegovy pricing page explains what a legitimate private prescription should include and the market context around current private prices.

If you would like a GPhC-registered prescriber to review your circumstances and advise on whether semaglutide at the initial dose steps or semaglutide at the higher maintenance doses is appropriate for you, speak to our prescribers, the consultation is free, and there is no obligation.