When Wegovy Side Effects Start — and What to Expect Week by Week

The first 48 hours: what most people notice after injection one

Picture this: you've taken your first 0.25mg Wegovy injection on a Sunday evening, and by Monday morning your stomach feels unsettled. That is textbook. The most common early side effects are nausea, a reduced appetite, burping and mild indigestion. Some people also notice a slight headache or fatigue. If you are curious about how fast Wegovy side effects start, the short answer is that they can appear within hours of the first dose, because semaglutide slows gastric emptying, food sits in your stomach longer, signals of fullness fire sooner, and your gut takes a little time to recalibrate.

For most people, this first wave of nausea is mild and passes within two to four days. Eating smaller portions, staying upright after meals and avoiding fatty or spicy food can help considerably. The 0.25mg starting dose is chosen specifically because it gives your digestive system time to adjust before the dose increases, the aim is tolerability, not weight loss, at this stage. If you have questions about how the escalation schedule works, our frequently asked questions cover the schedule in plain language.

A smaller proportion of people do experience vomiting or diarrhoea in week one. If either is significant enough to stop you drinking fluids, that changes the picture, see the section below on when to get help.

Dose-increase weeks: why side effects can return each time the dose steps up

Wegovy is titrated in roughly four-week steps: 0.25mg, then 0.5mg, 1.0mg, 1.7mg and, for most people, 2.4mg as the maintenance dose (or up to 7.2mg if your prescriber moves you to the higher licensed strength). Each step up can bring a fresh, shorter round of side effects, the same GI symptoms as week one, but typically milder each time because your system is becoming more familiar with the medicine.

The pattern is predictable enough that planning around it helps. Understanding when Wegovy side effects start at each new dose level means you can arrange a lighter lunch on a Friday if you know Thursday is injection day and queasiness tends to follow. That kind of small adjustment is worth discussing with a prescriber before your dose changes rather than after. You can read more about what to expect across the full side-effect range on our Wegovy side effects overview.

Most people find the dose-increase dips get shorter and less intense as treatment progresses. By the time maintenance dose is reached, many report the GI side effects have largely settled. Constipation occasionally becomes more of a factor at higher doses, where nausea has faded, worth knowing about in advance and easy to manage with adequate hydration and fibre.

When do Wegovy side effects stop? The maintenance phase picture

Once you have been on the same dose for several weeks, side effects for most people reduce to background level or disappear altogether. The body adapts. NHS guidance notes that GI effects are generally most troublesome at the start and during escalation, and that they tend to ease over time, consistent with what participants reported in the STEP 1 clinical trial, published in the New England Journal of Medicine. For a closer look at when semaglutide side effects start and how the pattern typically unfolds, our dedicated page walks through the timeline in detail.

A minority of people do experience ongoing nausea throughout treatment, particularly with higher doses. If side effects at maintenance dose are still disrupting daily life after four to six weeks, that is a conversation to have with your prescriber, not a reason to stop unilaterally. Our clinical team, led by our lead prescriber, provides priority aftercare seven days a week precisely for this kind of check-in.

Stopping Wegovy brings its own considerations. Some people notice appetite returning and experience weight regain after stopping the medicine, a separate topic covered on our page about what happens when you stop Wegovy, and something to factor in when planning treatment with your prescriber.

When to get medical help: symptoms that should not wait

The vast majority of Wegovy side effects are uncomfortable rather than dangerous. But some symptoms need same-day or emergency medical attention. The MHRA issued a Drug Safety Update in January 2026 specifically highlighting acute pancreatitis as a known, though infrequent, risk with GLP-1 medicines: the key warning sign is severe stomach pain that does not settle and radiates through to the back, sometimes with vomiting. Knowing how soon side effects of Wegovy start can help you tell the difference between expected early symptoms and anything that warrants urgent assessment, not a wait-and-see approach.

Other symptoms that need prompt attention include: signs of a serious allergic reaction (swelling of the face, throat or lips; difficulty breathing; rapid heartbeat); persistent vomiting or diarrhoea severe enough to prevent keeping fluids down, which can lead to dehydration and kidney strain; and gallbladder symptoms such as sharp pain in the upper right abdomen, particularly after eating. The NHS England guidance on weight management injections covers these warning signs clearly and is worth reading before you start treatment.

If you experience something you are unsure about, contact our aftercare team or call 111. If you think you are having a serious reaction, call 999. You can also report any suspected side effect directly to the MHRA via the Yellow Card scheme, the link is in the safety facts panel above. Reporting helps regulators build a clearer picture of how these medicines perform in real-world use, and it genuinely matters.

Our prescribers discuss side-effect timing, management and red-flag symptoms as part of every consultation, check your eligibility to see whether Wegovy could be clinically suitable for you.