How Soon Do Side Effects from Wegovy Start?

The first 48 hours: what most people actually feel

Picture this: you've done the consultation, a plain box arrived via DPD, and you've given yourself your first injection. By that evening, or the following morning, a dull nausea sets in. For many people this is exactly how the first week goes, not dramatic, but noticeable. Nausea, burping, a feeling of fullness that arrives earlier than expected at meals, and sometimes loose stools are all common in those opening days. Headache and fatigue also show up for some. These effects tend to peak somewhere in the first week and begin easing by week two, though the timeline for how soon you feel side effects of Wegovy differs between people. A question our prescribers hear regularly: "Is this normal?" For mild GI symptoms in week one, the answer is usually yes. The full Wegovy side-effect picture is worth reading before you start, so nothing catches you off guard.

The semaglutide in Wegovy slows how quickly your stomach empties, which accounts for most of these early feelings. That mechanism is also largely responsible for the appetite reduction that makes the medicine work. Knowing the two are linked can make the first week feel less worrying. Staying well hydrated and eating smaller, lower-fat meals tends to help.

Dose increases: why side effects can come back

Wegovy is titrated gradually, the dose steps up approximately every four weeks, following a schedule your prescriber sets. Many people find that each increase brings a brief return of the nausea and loose stools they thought they'd got past. This is expected. The pattern typically mirrors the opening week: noticeable for a few days, then easing as the body adjusts to the new level. It does not mean treatment is failing or that you're more sensitive than average. It means your dose has changed and your system is catching up. For a closer look at how soon side effects of Wegovy tend to appear at each stage, this page covers the duration question in more detail.

A few things make dose-increase side effects more manageable: eating before the injection window if your prescriber allows, avoiding very fatty or rich meals on injection day, and giving yourself a low-key evening. These aren't medical instructions (your Patient Information Leaflet and prescriber are the right source for personal guidance) but they reflect what many people find useful. If symptoms at a new dose are severe or don't settle within two weeks, speak to your clinical team rather than assuming it will pass.

When to get medical help without waiting

Most Wegovy side effects are self-limiting and mild to moderate. A few are not. The MHRA issued a Drug Safety Update in January 2026 specifically highlighting acute pancreatitis as a known, infrequent but potentially serious risk with GLP-1 medicines: severe stomach pain that doesn't ease and may radiate through to the back, with or without vomiting, needs same-day medical attention. Don't wait for a scheduled review. The same applies to signs of a serious allergic reaction (swelling around the face or throat, difficulty breathing) and to significant dehydration caused by persistent vomiting or diarrhoea. Gallbladder problems can also occur; right-sided or centre-upper abdominal pain is worth reporting promptly to a GP or 111. The MHRA Yellow Card scheme is also open to patients: if you experience something unexpected on Wegovy, you can report it there directly, and those reports contribute to ongoing safety monitoring.

If you're unsure whether what you're feeling needs attention, call 111 or speak to your GP. For questions specifically about how your treatment is going, our aftercare team is available seven days a week.

Side effects that are less common but worth knowing about

Beyond the GI effects, some people report dizziness, injection-site redness or itching, and (less often) changes in heart rate. Hair thinning has been noted in clinical trial data, typically attributed to rapid weight loss rather than semaglutide itself, and usually temporary. Mood changes are reported rarely; if you notice low mood or any thoughts of self-harm, contact your GP or a mental health service promptly. People with a history of diabetic retinopathy should be aware that rapid glucose changes can affect the eyes, a detail to raise at your initial consultation if it applies to you. Wegovy is not licensed for use in pregnancy, while breastfeeding, or for those trying to conceive; it is also not licensed for anyone under 18. These aren't edge-case exclusions, they're absolute, and any prescriber should screen for them. Many people also want to know how soon after taking Wegovy you get side effects, which is covered in detail for anyone preparing for their first dose. For broader context on what Wegovy is and how it works, the Wegovy overview covers the treatment as a whole. Our clinical team reviews every consultation personally, and discussing your medical history in full is exactly how side-effect risk gets properly assessed before treatment begins.