Most people who experience side effects from Wegovy notice them within hours to a few days of their injection. The drug reaches its peak concentration in your blood at a median of about 24 hours after the shot, with a range of 3 to 48 hours, which lines up closely with when symptoms tend to appear.
The First 24 to 48 Hours
Semaglutide, the active ingredient in Wegovy, absorbs gradually from the injection site. For most people, blood levels peak around the 24-hour mark, though some people hit that peak as early as 3 hours or as late as 48 hours. This variation helps explain why two people can take the same dose and have very different experiences with timing. One person might feel nauseous by bedtime on injection day, while another won’t notice anything until two or three days later.
Nausea is the most commonly reported early side effect and often the first one people notice. It can range from a mild queasiness that comes and goes to a more persistent feeling that affects your appetite for a day or two. Vomiting, if it happens, typically follows a similar timeline.
Gut-Related Side Effects and When They Appear
Beyond nausea, the most frequent side effects are digestive: diarrhea, constipation, bloating, and gas. These can show up within the first week of treatment, though the exact day varies from person to person. You’re at the highest risk for diarrhea and constipation when you first start the medication or when your dose goes up.
These gut symptoms happen because semaglutide slows the rate at which your stomach empties food into your intestines. That slowdown is part of how the drug reduces appetite, but it also means food sits in your digestive tract longer than usual, which can cause discomfort, fullness, and changes in bowel habits. For some people these effects are mild and barely noticeable. For others, they can be disruptive enough to affect daily routines during the first week or two at a new dose.
Why Dose Increases Restart the Clock
Wegovy uses a gradual dose-escalation schedule, starting low and increasing every four weeks. Each time your dose goes up, your body has to adjust to a higher level of the drug, and side effects can return or worsen even if they had faded at the previous dose. This means the question of “when do side effects start” isn’t just about your first injection. It’s relevant at each step up.
The pattern tends to repeat: side effects appear within the first few days of the new dose, peak during the first week or two, then gradually ease as your body adapts. Some people breeze through every increase with minimal symptoms, while others find certain dose levels harder to tolerate than others.
How Long Side Effects Typically Last
Most side effects are temporary, lasting anywhere from a few days to a few weeks. Gastrointestinal symptoms like nausea, diarrhea, and constipation tend to improve as your body gets used to the medication. For many people, the worst of it is concentrated in the first couple of weeks at each dose level.
That said, semaglutide has a long half-life of roughly one week, meaning it stays active in your system for a prolonged period. After any given dose, the drug remains in your circulation for about 5 to 7 weeks. This is why side effects don’t disappear overnight if they do occur. The drug clears slowly, and your body needs time to adjust to its continuous presence. The upside of that slow clearance is that once your body does adapt, symptoms tend to stay manageable as long as your dose remains steady.
What Affects Your Personal Timeline
Several factors influence how quickly side effects show up and how intense they feel. People who are more sensitive to changes in digestion, those with a history of gastrointestinal issues, or those who eat large or high-fat meals around injection time may notice symptoms sooner or more severely. Staying hydrated, eating smaller meals, and avoiding foods that are greasy or very rich can make the adjustment period more comfortable.
The timing and severity also vary simply because of individual biology. Some people metabolize the drug slightly faster or slower, their gut bacteria differ, and their baseline digestive function is unique. There’s no reliable way to predict exactly when or whether you’ll feel side effects, but the general window of hours to days after each injection holds for the large majority of users.