Semaglutide Week 2: What Your Body Is Actually Doing

You've done your first injection. Now what?

Picture the scene: Sunday evening, you did your first Wegovy injection last week, and now you're a fortnight in. You might have felt a little nauseous after the first dose, eaten noticeably less at a couple of meals, or felt almost nothing different at all. All three are well within the normal range at this stage. The 0.25 mg dose is deliberately low, the NHS describes it as a tolerability step rather than a therapeutic target, and the NHS medicines guidance on semaglutide confirms that dose escalation happens gradually over several months. The medicine's job in these early weeks is simply to let your body get used to its presence.

Appetite changes in week two are real but uneven. Some people notice a genuine reduction in hunger; others find the effect is subtle until around week four or five when the dose increases. That variability is normal. The mechanism (semaglutide acting on GLP-1 receptors to slow gastric emptying and signal fullness to the brain) takes time to settle into a consistent rhythm. If you're curious what a slightly longer window looks like, our page on what to expect at week four covers the picture once the first dose increase has had time to bed in.

One thing worth knowing: the timing of your injection day matters less than keeping it consistent. A patient who started on a Friday and then travels the following week sometimes worries about the gap. As long as you follow your prescriber's schedule and the Patient Information Leaflet, a stable day each week is all that's needed.

Side effects tend to peak here, what that looks like and when to act

Week two is often when gastrointestinal side effects are most noticeable. Nausea is the most commonly reported: it tends to sit at a low level rather than the acute kind associated with illness, often arriving after meals rather than continuously. Loose stools, indigestion, burping and a general sense of fullness even after eating a small amount are also common. Most people find these settle within ten to fourteen days of any given dose. Fatigue and mild headaches appear in some cases too, likely connected to reduced food intake.

The main flag to watch for is severe, persistent abdominal pain that radiates to the back. The MHRA issued a Drug Safety Update in January 2026 specifically highlighting acute pancreatitis as a known but uncommon risk with GLP-1 medicines; that kind of pain warrants urgent medical attention, not a wait-and-see approach. Dehydration from repeated vomiting or diarrhoea is a separate concern worth taking seriously, sip fluids steadily rather than in large amounts if nausea is present.

Keeping portion sizes small, avoiding high-fat or spicy meals, and eating slowly all help manage the adjustment period. These aren't permanent restrictions; they're practical measures for the weeks when your digestive system is settling. If you're finding week two harder than expected, our prescribers are available for aftercare seven days a week.

How much weight loss is realistic in the first two weeks?

Honestly, not a lot, and that's fine. In the STEP 1 trial, which tracked semaglutide 2.4 mg over 68 weeks against placebo in nearly 2,000 adults with obesity, the average weight reduction by the end of the trial was around 15%. Almost none of that happened in weeks one and two. Early changes on the scale tend to reflect water loss and a reduction in calorie intake rather than meaningful fat loss. The medicine reaches full effect gradually, so measuring progress week-by-week this early produces an unreliable picture.

If you want a broader sense of the timeline, our piece on how long Wegovy takes to work covers what the trial data shows across the full escalation schedule. For context on the two-week mark specifically, semaglutide two-week results looks at what is and isn't a reliable signal this early. The short version: week two is too early to judge. Consistency with injections and lifestyle changes matters more right now than any number on the scales.

It's also worth knowing that cost shouldn't drive you towards an unsupervised route. Private treatment through a legitimate UK provider includes clinical oversight; understanding what that looks like in practice is more useful than comparing headline prices. For those curious about what the full private route involves, our treatment overview sets out the options clearly.

What week two tells your prescriber, and what to track

The main clinical question at this stage is tolerability. Your prescriber is watching for two things: whether you're managing side effects well enough to continue, and whether anything in your response flags a reason to adjust the plan. This is why clinical re-review before every repeat matters, it isn't bureaucracy, it's the mechanism that keeps treatment safe.

What's worth noting down yourself: how your appetite feels around mealtimes, whether nausea is affecting your ability to eat or drink normally, any stomach pain (its location and whether it persists), and your energy levels. You don't need a spreadsheet, a few honest notes on your phone is enough. These observations help a prescriber make a better decision than a simple tick-box review could.

If week one felt quite different from week two, that's also normal, the medicine accumulates slightly each week until a steady state is reached, so week two often feels more pronounced than week one. Our page covering what happens in week one explains the baseline, and what changes by week three gives the next reference point. The pattern across the first month is more informative than any single week in isolation. If treatment is something you're considering, starting a free consultation with our prescribers is the first step.