Wegovy week 4 side effects: what's normal, what isn't, and when to call for help

Week 4 in context: where you sit in the titration schedule

Wegovy's dose ladder climbs slowly for good reason. You start at 0.25mg, move to 0.5mg after four weeks, then to 1.0mg at week 9, and continue upward through 1.7mg before reaching the 2.4mg maintenance dose. Week 4 is your final week at 0.5mg, still well below the doses where the most significant weight loss occurs. That matters, because people sometimes worry that side effects this early mean the medicine isn't for them. Usually it means the opposite: your system is responding, and it needs a bit of time.

A question our prescribers hear most weeks is whether GI symptoms in early weeks are a sign to stop. In the vast majority of cases they're not. The NHS semaglutide medicine guide describes nausea, diarrhoea, constipation, indigestion, burping and vomiting as common, particularly after starting or moving up a dose. At 0.5mg, you're still in the adjustment phase. The full overview of Wegovy side effects covers what changes as the dose increases.

Semaglutide slows gastric emptying, food moves through the stomach more slowly, which is part of how it reduces appetite. That slowing is also why your digestive system can take a few weeks to adapt. Most people find the worst of the nausea is earlier: if you want a reminder of what that looked like, you can read about the side effects most people experience in their first week on Wegovy on our dedicated page. By week 4, some people feel noticeably better; others are still navigating it.

What's normal to feel in week 4, and how to manage it day to day

At the 0.5mg dose, the symptoms most commonly reported are nausea (especially after meals), loose stools or constipation, low-grade fatigue, headache and reduced hunger. Injection-site reactions (mild redness or a small lump where the pen was used) are also common and not usually cause for concern.

Practical steps that help: eating smaller portions and avoiding rich, fatty or very spicy food reduces nausea noticeably for many people. Staying well hydrated is genuinely important, partly because GI symptoms can lead to fluid loss, and partly because dehydration worsens headaches and fatigue. Protein at each meal helps maintain muscle mass when overall intake drops. If constipation is the main issue, increasing fibre and water intake is the standard first step, laxatives are sometimes used short-term but should be discussed with your prescriber first.

Fatigue in week 4 is often underreported. If you're eating less and your body is adjusting to altered gut-hormone signalling, feeling tired makes physiological sense. It typically improves. If fatigue is severe or accompanied by dizziness on standing, let your prescriber know. You can find notes from earlier in treatment (including how symptoms tend to shift) on the week 2 side effects page and the week 3 side effects page for comparison.

When to get medical help, and when to contact your prescriber

Most week-4 symptoms are manageable. But some require prompt action, and it's worth being clear on the difference before you need to use it.

Seek urgent medical attention if you develop severe or persistent stomach pain, particularly pain that spreads to your back, with or without vomiting. In January 2026, following its review of GLP-1 medicines, the MHRA issued a Drug Safety Update highlighting acute pancreatitis as a known but infrequent risk, the key symptom pattern is exactly that: intense abdominal pain reaching through to the back. Go to A&E or call 999 if the pain is severe.

Also seek help promptly for signs of an allergic reaction (swelling of the face, throat, tongue or difficulty breathing), persistent vomiting or diarrhoea that's preventing you from keeping fluids down (dehydration can affect kidney function), and for any thoughts of self-harm or significant mood changes, these are listed in Wegovy's patient information leaflet and should be taken seriously.

Contact your prescriber or GP (rather than A&E, unless symptoms are severe) for anything that's disrupting daily life: nausea that won't settle, injection-site reactions that aren't improving, or uncertainty about whether to continue to the next dose. You can also report any suspected side effects directly through the MHRA's Yellow Card scheme, it's open to patients and helps regulators monitor real-world safety data for medicines like Wegovy.

Whether to continue, pause or adjust: your prescriber decides, not the internet

Week 4 is one of the moments where people make decisions about their treatment that genuinely benefit from clinical input. Some people hit week 4 feeling fine and ready to move forward. Others feel rough enough that an extended time at 0.5mg (rather than moving to 1.0mg as scheduled) makes more sense. Both are legitimate outcomes. The titration schedule is a guide, not a contract.

What isn't useful is stopping abruptly based on a bad week without speaking to someone first. Side effects that feel significant to you might be easily managed with a simple adjustment. And side effects that seem minor might occasionally warrant investigation. That's the value of clinical oversight: the prescriber is reading your full picture, not just one symptom.

At nume, our prescribers discuss side effects as a standard part of the consultation, including what to expect at each dose stage and how to manage common symptoms. If you're considering starting treatment or want to understand what the process looks like, check your eligibility through a free consultation. You can also read more about the treatment itself on the Wegovy overview page, or explore all weight-loss treatments we offer.