Semaglutide at week 4: what's actually happening (and what isn't yet)

The biggest misconception: week 4 should look like the trial results

The STEP 1 trial, published in the New England Journal of Medicine, reported an average weight reduction of around 15% over 68 weeks at the 2.4 mg maintenance dose. That figure covers more than a year of treatment at the highest dose. Week 4 is the last week of the lowest dose, 0.25 mg, which exists purely to reduce early side effects, not to drive significant weight loss. Comparing your four-week result with a 68-week trial average is the single most demoralising thing a person can do at this stage, and it leads many people to conclude the medicine isn't working when it's actually behaving exactly as expected.

A more useful frame: week 4 is a tolerability checkpoint, not a results checkpoint. Your prescriber's main question at this point isn't "how much have you lost?", it's "have you tolerated the starting dose well enough to move up?" The therapeutic work begins in earnest after that transition.

If you want to understand the realistic timeline for meaningful change, the detail on how long Wegovy takes to work sets out what the evidence actually shows at each phase.

What is genuinely happening in your body by week 4

GLP-1 receptor agonists like semaglutide act on receptors in the gut and brain involved in appetite regulation and gastric emptying. By week 4, most people notice they feel satisfied with smaller portions, think about food less between meals, and find certain very rich or fatty foods less appealing than before. These are not placebo effects, they reflect real receptor activity. The reason weight loss may still be modest is that 0.25 mg is a fraction of the 2.4 mg dose the body will eventually receive; the signal is there, but it's been deliberately kept quiet while your digestive system adjusts.

One practical checking habit worth building now: photograph or note down what a typical meal actually looks like on a plate compared with four weeks ago. Most people, doing this for the first time, are genuinely surprised by how much smaller a portion satisfies them, a concrete signal the medicine is doing something, even when the scale has been uncooperative. The four-week results picture covers the range of what clinical experience and trial data suggest is typical at this early point.

Nausea and loose stools are the most common complaints in weeks 1 to 4. NHS guidance on semaglutide notes these tend to settle as the body adapts. If they haven't eased at all by week 4, or are interfering significantly with daily life, that's a conversation to have with your prescriber before the next dose step, not after it.

Week 4 in context: the dose steps ahead

After week 4 at 0.25 mg, the licensed titration schedule moves to 0.5 mg, then 1.0 mg, 1.7 mg, and finally 2.4 mg, each step held for roughly four weeks. The gap between where you are now and the maintenance dose is substantial, and weight loss typically accelerates as the dose increases. People who see very little change in weeks 1 to 4 sometimes see a more noticeable shift from week 8 onwards, once the dose is higher and appetite suppression deepens.

This is also a good moment to look back at the earlier weeks. If you found what semaglutide week 1 involves harder than expected, it's useful context for how you might approach the next dose change, slower titration is an option some prescribers use to manage persistent nausea. The week 3 experience is where many people start noticing the appetite shift more clearly, which can make week 4 feel anticlimactic by comparison if the scale hasn't followed.

For people who started Wegovy recently and want a broader sense of what the coming months look like, the Wegovy overview brings together the licensing, clinical evidence and practical details in one place. And if you're thinking further ahead, the timeline for losing 20 kg on Wegovy puts realistic expectations around a commonly asked target.

When week 4 raises real concerns

Most week-4 experiences are unremarkable in a reassuring way. A few signals are worth acting on promptly. Severe stomach pain that spreads to your back (especially with vomiting) needs urgent medical attention and may indicate pancreatitis, a known but uncommon side effect of GLP-1 medicines flagged in MHRA communications. Signs of dehydration from prolonged GI illness (dizziness, very dark urine, inability to keep fluids down) also warrant same-day contact with a clinician rather than waiting it out.

If you have questions about how your week 4 is going and whether continuing or adjusting is right for you, our prescribers are available seven days a week. You can review your treatment options and start a free consultation, a real clinician reads your answers the same day. For general questions about the service, our FAQs cover the most common queries about how the process works.