First dose of Wegovy: what to expect in the days ahead

What the STEP 1 trial data show about the first weeks on semaglutide

The picture of what happens early in Wegovy treatment comes partly from the STEP 1 phase 3 trial, 68 weeks, more than 1,900 adults with obesity, published in the New England Journal of Medicine. Gastrointestinal side effects were highest in the early weeks and clustered around dose escalation points, then declined. That pattern tells you something practical: the first dose is not necessarily harder than later ones, but the initial exposure is when your digestive system meets the medicine for the first time.

Average weight loss across the trial reached approximately 15% of body weight by week 68, but that result builds over months. What you feel in the first few days is almost entirely about tolerability, not yet about results. Appetite may already feel slightly different (semaglutide slows gastric emptying and acts on appetite-regulating pathways in the brain) but do not judge the treatment by day two.

Fatigue and headache are also listed as common reactions. For most people they are mild and brief. The NHS medicines page for semaglutide lists nausea, vomiting, diarrhoea, constipation, stomach pain, and burping as the most frequently reported effects, with injection-site reactions occasionally noted too.

Hour by hour: the first 72 hours after injecting Wegovy

Wegovy is injected once weekly, subcutaneously (into the abdomen, thigh, or upper arm) and the medicine's concentration in the blood rises slowly over the following day or so. Most people do not feel anything immediately after the injection itself beyond the minor sensation of the needle.

By the evening of day one, or morning of day two, a proportion of people notice nausea. It is rarely severe at 0.25 mg; for many people it is just a vague unsettled feeling. Eating a small, protein-led meal rather than a large or high-fat one before or around injection time helps. Timing your injection for a day when you are at home (not, say, a long drive or a work lunch) is worth considering. If the weekly injection falls on a payday Friday or just before a holiday, a modest, low-fat meal rather than a celebration dinner is genuinely practical advice.

By day three, most people feel close to their baseline again. If nausea is still significant by day four, tell your prescriber before your next dose, that is what aftercare support is for. Understand that the first dose is the 0.25 mg starter, and the full clinical picture of what this step involves is worth reading before you begin.

How the starting dose sets up the rest of treatment

The 0.25 mg dose is not where the clinical work of weight management happens. It is a deliberate low-level introduction: the prescriber's goal is to get you through the titration schedule (typically 0.25 mg for four weeks, then stepping up) with manageable side effects rather than a sharp shock to the system. Understanding exactly what the first dosage of Wegovy is and why it is set that low helps people stay on track when they feel the medicine is not yet doing much.

Appetite changes may be subtle at first. Do not add extra food to compensate or assume the medicine has not worked. Protein intake and hydration matter more than usual; when the gut is slowing down, constipation can be an issue if fibre and fluid are neglected. Light activity helps too, not for calorie reasons, but because it tends to reduce nausea.

For context on the schedule ahead, the full Wegovy dose ladder covers each step up to the 2.4 mg maintenance level, and many patients find it reassuring to see the whole journey laid out. If you are thinking further ahead, details on moving to the 1 mg stage give a preview of how the medicine tends to feel as tolerance builds, and you can also read about the 2.7 mg dose of Wegovy for an understanding of where the titration schedule goes beyond the 2.4 mg maintenance level.

When to get medical help, and how to report problems

Most first-dose effects are uncomfortable rather than dangerous. A small number of reactions need same-day medical attention. Severe, persistent abdominal pain that reaches into the back (with or without vomiting) can indicate acute pancreatitis, a known but uncommon risk with GLP-1 medicines. The MHRA highlighted pancreatitis in a Drug Safety Update in January 2026 and advises stopping the medicine and seeking urgent care if these symptoms appear.

Other situations that warrant a call to a doctor or 111: signs of a serious allergic reaction (facial swelling, difficulty breathing, a spreading rash), severe dehydration from repeated vomiting or diarrhoea, or any sudden vision changes. For anything less acute (persistent nausea across several days, injection-site soreness, constipation that is not resolving) your prescribing service's aftercare team is the first port of call.

You can report any suspected side effect directly to the MHRA at the Yellow Card scheme. This is open to patients as well as clinicians, and reports genuinely contribute to ongoing medicine safety monitoring.

For a broader overview of the treatment (how it works, who it suits, and the full Wegovy service at nume) the main treatment page covers the complete picture before you commit to starting.