What to expect from the Wegovy pen after 1 dose

The morning you inject for the first time

Picture yourself on a Sunday morning, pen in hand, reading the leaflet for the third time. You inject into your abdomen as instructed, put the pen back in the fridge, and wait. For many people, not much happens in the first 24 hours. That is normal, and it is not a sign that Wegovy is not working.

Semaglutide is a GLP-1 receptor agonist, meaning it mimics a gut hormone that signals fullness and slows the rate at which your stomach empties. After a single 0.25mg dose the blood concentration is low and rising gradually. Some people feel a faint reduction in appetite by day two or three; others feel nothing different for the entire first week. Both experiences sit within the expected range described in the Wegovy Summary of Product Characteristics on the eMC.

Nausea, if it comes, usually shows up in the first 48 hours after the injection and tends to be mild. Staying well hydrated, eating smaller portions, and avoiding rich or fatty food at that time are the practical steps most prescribers suggest. If you are unsure whether what you are feeling is within the expected range, the nume FAQs cover common first-week questions, and our clinical team is available seven days a week.

Why 0.25mg feels quiet, and what that means for your expectations

The 0.25mg starting dose is not a treatment dose. It exists so your body learns to tolerate semaglutide before the dose rises. You would not expect a car to reach motorway speed in first gear; the same logic applies here. Clinically significant weight loss in the STEP 1 trial (which reported around 15% average body weight reduction over 68 weeks) was achieved at the 2.4mg maintenance level, reached only after a multi-month titration schedule. That data comes from the STEP 1 trial published in the New England Journal of Medicine.

So if after your first pen you feel that very little has changed, that is by design. The goal in weeks one to four is tolerability, not transformation. Some people do notice reduced hunger even at this early stage (the medicine affects appetite signalling at any concentration) but it is genuinely variable. If you want to know more about how things typically develop once you move on, our page on what to expect from your Wegovy pen after 2 doses gives a useful picture of the early pattern.

If you want a clearer picture of how the dosing schedule builds from here, our page on Wegovy doses explains each step and what to expect at each level.

Side effects after the first pen: what is common, what needs attention

The most frequently reported side effects after early Wegovy doses are gastrointestinal: nausea, constipation, diarrhoea, burping, or a general sense of fullness after eating very little. These are most noticeable after the first injection or after a dose increase, and for most people they settle within a week or two as the body adjusts.

A small number of people experience headache, fatigue, or dizziness in the first days. Injection-site reactions (mild redness or itching at the abdomen, thigh, or upper arm) are also possible and usually pass quickly. Rotating your injection site each week helps reduce localised irritation.

One symptom that always warrants urgent medical attention is severe stomach pain, particularly pain that radiates towards the back, with or without vomiting. This can be a sign of pancreatitis, which the MHRA highlighted as a known but infrequent risk associated with GLP-1 medicines. Do not wait to see if it passes, contact 111 or your GP straight away. You can also report any suspected side effect through the MHRA Yellow Card scheme.

For most people, though, the first pen is uneventful. A mild nausea that peaks Tuesday afternoon and fades by Wednesday (perhaps during the commute rather than anything more dramatic) is the reality for many. Serious reactions at 0.25mg are uncommon.

What happens next, and when to speak to your prescriber

After four weeks at 0.25mg, the standard schedule moves to 0.5mg, and the dose increases continue in roughly four-week steps until you reach your maintenance level. Each increase may bring a brief return of mild nausea as the body re-adjusts, which is why the titration is staged rather than rushed.

Your prescriber reviews your treatment before any dose change at nume. If you experienced side effects that were more persistent than expected, or if you felt no effects at all and have questions about whether the medicine reached you correctly, those are exactly the conversations the clinical review is for. You can also read about what to expect from your Wegovy pen after 4 doses, which covers the point at which many people begin to notice more consistent changes. You can read about what to expect after each Wegovy dose step as your treatment progresses.

Wegovy is a prescription-only medicine that requires ongoing clinical oversight, doses are not changed on personal initiative. If you are thinking about starting treatment and want to understand whether it could be appropriate for you, our free consultation is reviewed the same day by a GPhC-registered prescriber. There are also broader questions about the treatment covered on our Wegovy overview page, and if you are weighing up cost alongside everything else, our guidance on accessing Wegovy in the UK covers what to look for in a regulated provider.