What to Expect in Week 1 of Wegovy

Why does week one feel underwhelming compared to what you expected?

Most people arrive at their first injection with a mix of excitement and nerves, and then week one passes without the dramatic shift they had imagined. That is entirely by design. Semaglutide, the active ingredient in Wegovy, works by activating GLP-1 receptors that influence appetite, satiety and the speed at which your stomach empties. At 0.25mg the dose is low enough that these effects are modest, your system is being introduced to the medicine, not fully treated by it. If you want a detailed picture of what to expect as those first seven days unfold, our guide to the first week on Wegovy walks through the experience day by day, covering everything from the injection itself to how your appetite and energy levels typically respond. Think of it as a calibration week rather than a treatment week.

The NHS medicines page for semaglutide confirms this graduated approach: the dose is stepped up roughly every four weeks by your prescriber until you reach the maintenance dose that works for you. Appetite suppression becomes more noticeable as the dose rises. If you feel relatively normal through week one, that is a good sign, your body is tolerating the medicine well. If you feel rough for a day or two, that is also normal, and it usually improves quickly.

For a broader sense of how the weeks ahead typically unfold, the full Wegovy treatment timeline covers what most people notice at each stage of titration.

What side effects actually show up in week one, and what do you do about them?

Nausea is the headline. It affects a meaningful proportion of people starting Wegovy and is most intense in the 12 to 24 hours after the injection, then tends to fade. Vomiting, loose stools, constipation, indigestion and a general feeling of fullness after eating very little are all reported in week one. Fatigue and mild headaches come up too, often linked to eating and drinking less than usual.

Practical things that help: eating smaller portions and avoiding rich, fatty or very spicy meals in the first few days; keeping fluids up even when you do not feel thirsty; and taking the injection on a day when you can rest if needed. Some people find keeping their pen in the fridge door is a useful habit anchor, it becomes part of the same routine as making breakfast, a small reminder that consistency matters more than perfection.

The one situation that needs urgent attention is severe, persistent stomach pain that spreads to the back, with or without vomiting. That pattern can indicate pancreatitis, which the MHRA flagged in its Drug Safety Update for GLP-1 medicines as a known but infrequent risk. If that happens, stop the injection and get medical help the same day. Ordinary nausea does not need emergency care; that specific pain pattern does.

If you want to map week one against what typically follows, you can read about what most people notice when they reach week two of Wegovy, which is often where the first real appetite shifts start to register for some people.

Will you lose any weight in week one of Wegovy?

Probably not, or not noticeably. The scale may move slightly downward because you are eating a little less, or it may not move at all. Both outcomes are clinically unremarkable at this stage. The STEP 1 trial, which followed 1,961 adults over 68 weeks at the 2.4mg maintenance dose, reported an average body-weight reduction of around 15%, and that figure represents nearly a year and a half of treatment, not a single week at a starter dose.

What week one does do is establish the habit: the injection day, the storage routine, the awareness of how your body responds. Those foundations matter. People who understand from the outset that Wegovy is a long-arc medicine tend to stay with it through the early weeks when results are invisible. If you are curious about the longer timeline, how long Wegovy takes to work sets out realistic expectations across the full titration journey, and week five is typically where the first clear appetite changes become hard to ignore.

You can also read more about Wegovy as a treatment to understand the clinical evidence behind it, including the licensed doses and eligibility criteria, so your expectations going into week one are anchored in the actual data.

Is there anything you should check with your prescriber before or during week one?

A few things are worth knowing before your first injection. If you take oral contraceptives, the NHS guidance on weight-management injections advises adding a non-oral method of contraception for the first four weeks of tirzepatide, that specific interaction is most documented for tirzepatide rather than semaglutide, but it is worth raising with your prescriber if you are on the pill. Separately, if you are taking any other medicines that need careful timing with food or other drugs, flag this at consultation: slowed gastric emptying can affect how other medicines are absorbed.

You should also know about the Yellow Card scheme. If you notice a side effect that concerns you, you can report it directly at the MHRA's Yellow Card service, this is open to patients, not just clinicians, and genuinely contributes to national medicine safety monitoring. It is not a substitute for calling your prescriber or 111 if something feels urgent, but it is a useful channel for less acute concerns.

If you are considering starting Wegovy privately and want a same-day clinical review by a registered prescriber, speak to our prescribers about your eligibility and what the treatment journey looks like from week one onwards.