Your first day on semaglutide: what actually happens

Choosing when to do your first injection

Pick a day and time that suits your routine, because you'll repeat it every week. Many people choose a weekend morning when they're not rushing, there's no clinical reason to prefer morning over evening, but consistency helps. Once you've chosen, that becomes your weekly anchor point.

The injection itself is straightforward with a pre-filled Wegovy pen. Pinch the skin lightly, press the pen against the site, and hold it in place for the full count the Patient Information Leaflet specifies. Your prescriber and the leaflet are the authoritative guides here; technique details are worth reading before you start rather than after. A practical note: keep the pen refrigerated at 2–8°C until you need it, and let it reach room temperature for a few minutes first, cold injections can be more uncomfortable. For the exact storage and room-temperature window, always check the leaflet that comes with your pen.

If you want a fuller walkthrough of the injection process itself, our page on your first Wegovy injection covers technique step by step. And if you're curious about how semaglutide has been used clinically before it reached you, there's context on when semaglutide was first used in medicine.

What you'll probably feel, and what would be unusual

At 0.25 mg, most people's first day is unremarkable. The dose is low enough that appetite suppression is minimal and side effects are uncommon. Some people notice mild nausea a few hours after the injection; a small number feel nothing at all for the first couple of weeks. Both are normal. If you want to know what to expect more specifically, our page on your first day taking semaglutide walks through the timeline in detail.

What's worth knowing is that the GI effects associated with semaglutide (nausea, occasional loose stools, indigestion) tend to follow dose increases more than they follow day one. The NHS notes that these effects are typically mild and often settle within days to a couple of weeks as your body adapts. The clinical trial that underpins Wegovy's licence, the STEP 1 study published in the New England Journal of Medicine, recorded nausea as the most common side effect but also found it was the main reason most participants didn't stop treatment.

What would warrant attention: severe stomach pain that radiates to the back, signs of an allergic reaction (swelling, breathing difficulty, rash), or persistent vomiting that leads to dehydration. These are uncommon but should prompt you to contact your prescriber or, if urgent, 111 or A&E. The MHRA maintains a Yellow Card scheme at yellowcard.mhra.gov.uk where any suspected side effect can be reported directly.

If you're unsure whether something you're feeling is expected, our page on what to expect the first time you use Wegovy goes into more detail.

What to eat, and the question of timing

There's no required fast before or after your Wegovy injection. Unlike the oral semaglutide tablet (which needs to be taken on an empty stomach), the weekly injection has no food-timing rule attached to it. That said, most people find that lighter meals on injection day reduce any mild nausea, heavy, greasy food tends to amplify it.

Protein intake matters more than it might seem on treatment. As appetite falls over the coming weeks, the risk is eating too little rather than too much, and particularly skimping on protein. NHS guidance on healthy weight management during treatment recommends maintaining adequate protein and fibre alongside any calorie reduction, with activity built in alongside, these aren't optional extras but part of how the treatment is designed to work.

For a broader look at the treatment and how it fits into a weight management plan, the Wegovy overview page covers the full picture, including what the licence covers and who it's designed for. If cost or access are on your mind at this stage, the weight loss treatment page has honest context on the private route.

What happens after day one

The first day is the beginning of a titration schedule that typically runs over several months. Wegovy's maintenance pathway moves through increasing doses, the prescriber decides the pace based on how you're tolerating each stage. A dose is not usually increased until you've been stable on the current one for around four weeks, and clinical review happens before each step up.

This is also where ongoing support matters. Questions come up: what to do if you're under the weather, whether a stomach bug means you should skip a dose, how to handle a missed injection. These are conversations for your prescriber rather than guesswork. Our page on whether to take Wegovy when you have flu covers one of the more common mid-treatment questions. And if you want a prescriber to review your situation from the start, the free consultation at nume is reviewed the same day by a real clinician (not software) with aftercare available seven days a week once you're on treatment.

For detailed information on semaglutide as a medicine, the NHS semaglutide page is a clear, patient-level reference worth bookmarking before you begin.