What to Expect on Your First Day of Wegovy

What the STEP 1 trial tells us about the early weeks

The pivotal trial behind Wegovy's UK licence, STEP 1, published in the New England Journal of Medicine, ran 68 weeks and found an average weight loss of around 15 % at the 2.4 mg maintenance dose. That figure comes after a 16-week escalation period during which participants were on lower doses, including the 0.25 mg level where you begin on your first shot of Wegovy. Knowing that tells you something useful: the first few weeks are not where the clinical results were made. They are the foundation.

Gastrointestinal effects were the most frequently reported events in the trial. Nausea affected a substantial proportion of participants, particularly in the early titration phase, and was described as mild to moderate in the majority of cases. This is consistent with what the NHS's semaglutide medicines page describes: nausea, vomiting, diarrhoea and constipation are common, especially around dose changes, and tend to settle as the body adapts. Knowing that the discomfort typically follows a pattern (peaking in the hours after injection and often easing before the next dose) makes it considerably less alarming when it arrives.

If you've been reading about starting semaglutide for the first time and feel a mix of nervousness and cautious optimism, that's an entirely reasonable place to be. The medicine has a robust evidence base, but it is still a new experience for your body.

The practicalities of injecting on day one

Wegovy comes as a pre-filled pen. You do not need to draw up a dose or handle a vial. After washing your hands, choose a clean patch of skin (the abdomen (avoiding a 5 cm radius around the navel), the front of the thigh, or the upper arm) and follow the instructions in your Patient Information Leaflet step by step. The needle is fine and short; most people report that the injection itself is far less noticeable than they expected.

Timing is flexible. You can inject at any point during the day, with or without food. Picking a consistent time on the same day each week helps build the habit. Some people prefer a weekend morning when they can rest if nausea arrives; others find a weekday routine easier to maintain. There is no clinically superior moment, this is entirely about what you will actually do reliably.

If you'd like a broader picture of how to approach using Wegovy for the first time, our treatment overview covers the process from prescription to first dose in more detail. For questions about cost or what a private prescription includes, the Wegovy treatment page sets out what is involved.

Side effects on the first day: what's normal, what warrants attention

Mild nausea in the hours after your first injection is the most common experience. It usually arrives within two to four hours, plateaus, then fades, often gone by the following morning. Eating a small, low-fat meal before injecting and drinking water steadily through the day can help. Fatty or very rich food tends to worsen nausea on semaglutide, so your first injection day is not the occasion for a celebratory takeaway.

Headache, fatigue, and a general sense of digestive sluggishness are also reported, particularly in the first 24 hours. These are consistent with what early experiences on semaglutide commonly look like across the evidence base, and they generally resolve without intervention.

Some symptoms do require prompt medical attention: severe and persistent stomach pain that radiates to the back may signal pancreatitis, which the MHRA has highlighted as a known but infrequent risk with GLP-1 medicines. Signs of a serious allergic reaction, including swelling of the face or throat and difficulty breathing, also require immediate help. These events are rare, but they are the ones worth knowing about before day one, not after. If you have any concerns about side effects once you're on treatment, our clinical team is available seven days a week.

What does not happen on day one

Appetite suppression is real, but it builds gradually with timelapse. On your first day of Wegovy, don't expect to feel dramatically less hungry, that effect tends to become noticeable over several weeks, and more pronounced as the dose increases. Weight loss is similarly a medium-term picture; the 15 % average reduction in STEP 1 took 68 weeks to accumulate.

You also will not know on day one whether this medicine suits you long term. That assessment belongs to a prescriber, and at a regulated service it happens at every repeat review, not just at the start. If you're considering whether Wegovy or another weight-loss treatment is right for your situation, a clinical consultation is where that conversation properly begins. Our prescribers are not gatekeepers; they are the people who make the medicine safe to use.

For a fuller picture of semaglutide and how it works, including how it compares to other licensed options, the semaglutide overview is worth reading before or after your first injection. And if you want to understand what the Wegovy programme involves beyond week one, that page covers the titration journey through to maintenance dose.