How long do Wegovy side effects take to kick in — and how long do they last?

The first injection: what happens in the opening 48 hours

Picture this: you've done your first Wegovy injection on a Sunday evening, and by Monday morning you're wondering whether that mild queasiness is the medicine working or just nerves. For most people, it's the medicine. Semaglutide slows the rate at which food leaves the stomach and acts on appetite-regulating receptors in the brain, and the digestive system tends to make its feelings known quickly.

Nausea is the most frequently reported early symptom, and if you're wondering how long it takes to feel Wegovy side effects, it usually appears within 24 to 48 hours of the first injection. Burping, a feeling of fullness that arrives faster than usual, loose stools, or mild stomach discomfort can all feature in those opening days. Fatigue and a mild headache are also reported by some people. These effects are generally at their most noticeable in the first week, then tend to soften as the week progresses and the injection's concentration in the body begins to fall naturally before the next dose.

The NHS medicines page for semaglutide confirms that gastrointestinal effects are the most common reactions and typically improve over time. How long you personally feel them in those first days depends on factors your prescriber is best placed to discuss, including your diet, how much you ate around the injection, and any other medicines you take.

After each dose increase: why symptoms can come back

Wegovy is started at 0.25mg and titrated upward in stages, with each step representing a meaningful increase in the medicine's activity. It's common (and worth knowing in advance) that side effects can resurface, or intensify briefly, each time the dose goes up. This is not a sign something has gone wrong. It mirrors what happened at the start: the body is adjusting to a new level.

For many people the second round of nausea or digestive upset after a dose increase is shorter and milder than the first. Some people find the transition smoother if they avoid large, fatty or heavily spiced meals in the day or two around an injection. That said, any specific dietary adjustments during titration are something to raise with your prescriber rather than rely on general advice, everyone's situation is different.

Our page on how long Wegovy side effects last goes into more depth on what to expect across each titration step, including how the pattern shifts once you reach a maintenance dose.

Reaching a steady state: when most people find relief

After several weeks on a given dose, most people report that the worst of the gastrointestinal effects has settled. Nausea that was daily in week one often becomes occasional by week four or five, and for many people it fades almost entirely between injections. The stomach-emptying effect persists (that's central to how the medicine works) but the body's initial protest about it usually quietens down.

It's worth saying plainly: some people do continue to experience ongoing nausea or digestive discomfort throughout treatment, and a small number find it significant enough to affect their daily life. If you're still dealing with difficult symptoms after several weeks on a stable dose, that's worth raising with your prescriber rather than pushing through. Dose timing, what you eat before and after the injection, and whether another medicine might be contributing are all things a clinician can look at. You'll find practical questions our prescribers hear regularly on the Wegovy FAQs page.

If you're curious about how the overall treatment experience compares across people, the Wegovy treatment overview gives a fuller picture of both the evidence and what private treatment through a regulated pharmacy involves.

When to get medical help, and what not to sit on

The vast majority of Wegovy side effects are uncomfortable rather than dangerous. But a small number of reactions require prompt attention, and recognising them matters.

Severe, persistent pain in the abdomen (particularly if it spreads to the back, with or without vomiting) needs urgent medical assessment. The MHRA highlighted acute pancreatitis as a known but infrequent risk associated with GLP-1 medicines in a Drug Safety Update issued in January 2026; the message is not to alarm, but not to dismiss that pattern of pain as ordinary stomach upset either. Stop the injection and seek help the same day.

Signs of a serious allergic reaction (swelling of the face, lips or throat, difficulty breathing, or a severe rash) also require emergency care. Gallbladder problems, including pain under the right side of the ribs that may radiate to the shoulder, are another side effect to report to a doctor promptly rather than waiting it out. If you want a clearer sense of how long after taking Wegovy you feel side effects, significant dehydration from prolonged vomiting or diarrhoea can put pressure on the kidneys; if you cannot keep fluids down for more than a day, contact a healthcare professional.

For anything that concerns you but doesn't feel like an emergency, the team at nume's aftercare support is available seven days a week. And if you'd like to understand more about a specific symptom, the page on body aches as a Wegovy side effect is one example of how individual symptoms can be explored in more depth. Any suspected adverse reaction to a prescription medicine can also be reported to the MHRA directly through the Yellow Card scheme, patients as well as clinicians can submit reports.