Published On: 9th June, 2026
If you are considering or have recently started Wegovy for weight loss, understanding the potential side effects is an important part of managing your treatment confidently.
Most side effects associated with Wegovy (semaglutide) are mild to moderate and tend to improve as your body adjusts to the medication. However, knowing what to expect and when to seek advice can make a significant difference to your experience and your safety.
Wegovy works by mimicking a naturally occurring hormone called GLP-1, which regulates appetite and digestion. Because it affects the digestive system, most side effects are gastrointestinal in nature. They are most likely to occur when starting treatment or after a dose increase, and they often settle over time.
The table below summarises how common the main side effects are, based on clinical trial data.
| Side Effect | Frequency | When It Typically Occurs |
|---|---|---|
| Nausea | Very common | Early treatment or dose increases |
| Diarrhoea | Very common | Early treatment or dose increases |
| Constipation | Very common | Throughout treatment |
| Vomiting | Very common | Early treatment or dose increases |
| Headache | Common | Early treatment |
| Fatigue | Common | Early treatment |
| Injection site reactions | Common | Any point during treatment |
| Pancreatitis | Uncommon | Any point during treatment |
Nausea is the most frequently reported side effect of Wegovy. It is particularly common during the early weeks of treatment and after each dose escalation. For most patients, it is manageable and improves significantly within a few weeks as the body adjusts.
Practical steps that may help include eating smaller meals, avoiding rich or fatty foods, eating slowly, and not lying down immediately after eating. If nausea is persistent or severe, speak to your clinician before stopping treatment, as there may be ways to manage it without discontinuing.
Some patients experience vomiting, particularly at the start of treatment or following a dose increase. Like nausea, this typically settles over time.
If you are vomiting repeatedly and cannot keep fluids down, you should seek medical advice promptly. Persistent vomiting can lead to dehydration and may also affect how well other medications are absorbed.
Diarrhoea is another very common early side effect. It is usually short-lived and resolves without intervention. Staying well hydrated is important, particularly if diarrhoea is frequent.
If loose stools persist beyond a few weeks or are accompanied by other symptoms, this should be discussed with a clinician.
Wegovy slows gastric emptying, which can lead to constipation in some patients. Unlike other gastrointestinal side effects, constipation may persist throughout treatment rather than improving quickly in the early weeks.
Increasing fibre intake, staying hydrated, and maintaining gentle physical activity can all help. A clinician or pharmacist can advise on suitable remedies if constipation becomes uncomfortable.
Headaches and fatigue are reported by some patients, particularly in the early stages of treatment. These are often linked to reduced calorie intake and changes in eating patterns rather than a direct effect of the medication itself.
Ensuring you are eating regularly, staying hydrated, and not cutting calories too aggressively can help manage these symptoms. They typically improve as your body adapts.
Because Wegovy is administered as a weekly subcutaneous injection, some patients notice redness, itching, bruising, or mild swelling at the injection site. These reactions are generally mild and short-lived.
Rotating the injection site each week and following the administration guidance provided with your medication can help reduce the likelihood of localised reactions. If you notice significant swelling, pain, or signs of infection at an injection site, seek medical advice.
Rapid weight loss of any kind, including that achieved with Wegovy, can increase the risk of gallstones. Wegovy has also been associated with gallbladder-related problems including gallstones and inflammation of the gallbladder (cholecystitis) in clinical trials.
Symptoms such as sudden upper right abdominal pain, pain that radiates to your shoulder or back, fever, or yellowing of the skin should be assessed by a doctor without delay. According to the Wegovy prescribing information, gallbladder disease is a recognised risk and patients should be informed of the symptoms to watch for.
Some patients taking semaglutide experience a small increase in resting heart rate. This is generally modest and not considered clinically significant for most patients, but it is monitored as part of ongoing clinical review.
If you notice a persistently elevated heart rate, palpitations, or feel your heart racing at rest, this should be discussed with your clinician.
While uncommon, there are some serious side effects that require prompt medical attention:
Patients with type 2 diabetes should be aware that rapid improvement in blood glucose control can be associated with temporary worsening of diabetic retinopathy. If you have diabetes and notice any changes in your vision during treatment, seek prompt medical review.
*If you suspect a serious allergic reaction or anaphylaxis, call 999 immediately and do not wait to contact your prescriber.
Most gastrointestinal side effects, such as nausea, vomiting, and diarrhoea, are most prominent in the first few weeks of treatment or after a dose increase. For the majority of patients they improve within the first few weeks of treatment or after the body has adjusted to a new dose. Side effects that persist beyond this should be discussed with a clinician.
Not necessarily. Nausea is very common and does not always mean the treatment is unsuitable for you. Before stopping, speak to your clinician. They may be able to offer practical advice, adjust the pace of dose escalation, or suggest ways to manage symptoms while allowing your body more time to adapt.
Contact your clinician or prescriber. There are practical steps that can often help, including reviewing your dose schedule, adjusting your diet around injection days, or temporarily pausing dose escalation. You should not feel that you have to simply push through side effects without support.
In some cases, yes. Mounjaro (tirzepatide) is a different medication that works on both GIP and GLP-1 receptors, and some patients may tolerate it differently to semaglutide. However, switching should always be done under clinical supervision. Your prescriber will assess whether switching is appropriate, advise on timing, and guide the transition safely. You should not switch between weight loss injections without medical guidance.
Side effects can be more pronounced after each dose increase, particularly gastrointestinal symptoms. This is why Wegovy is started at a low dose and increased gradually over several months. The slow escalation schedule is designed to give your body time to adjust and reduce the impact of side effects.
Seek urgent help if you experience severe abdominal pain, persistent vomiting where you cannot keep fluids down, signs of a serious allergic reaction such as facial swelling or difficulty breathing, or sudden upper abdominal pain that may suggest gallbladder problems. These symptoms should never be left unassessed.
No. While side effects are common, not everyone experiences them, and many patients tolerate Wegovy well. The likelihood and severity of side effects varies between individuals depending on factors such as starting dose, rate of escalation, diet, and individual response to the medication.
Understanding potential side effects before starting Wegovy puts you in a better position to manage them if they arise, and to recognise the small number of symptoms that warrant prompt medical attention.
For most patients, side effects are manageable and temporary. They are not a reason to avoid an effective treatment, but they are a reason to start with proper medical support behind you.
At RX Direct, our clinicians provide guidance throughout your weight loss treatment journey, not just at the point of prescribing. If you have questions about whether Wegovy is right for you, or want to understand your options including Mounjaro, speak to our team or start your consultation below.
Start your consultation today.
Explore the latest updates, expert tips, and health news from RX Direct. Our blog covers treatments, new medications, and helpful advice for managing your health online.
If you are taking Mounjaro or Wegovy for weight loss, you are likely already thinking carefully about what you eat. But what you drink matters just as much. Certain drinks can support your progress, help manage side effects, and complement the appetite-reducing effects of your medication. Others can quietly undermine your results without you realising. …
If you have been thinking about your weight or considering treatment options, you may have come across the term BMI. It is one of the most commonly used tools in clinical practice for assessing whether a person’s weight falls within a healthy range, and it plays an important role in determining eligibility for weight loss …
If you are considering Mounjaro for weight loss, you may have come across mentions of pancreatitis as a potential risk. It is natural to want to understand what that means before starting treatment. The important context is this: the risk is real but rare, and for the vast majority of suitable patients, Mounjaro is a …
If you are comparing Wegovy vs Mounjaro, you are likely looking into prescription weight-loss treatment options that may support a wider medical weight management plan. Both treatments are once-weekly injections used alongside lifestyle measures such as a calorie-controlled diet, regular physical activity, and ongoing clinical support. Both can play a role in helping eligible adults …
Interest in weight loss jabs has increased significantly in recent years as new medications have been developed to help support long-term weight management. These injectable treatments can help reduce appetite, regulate blood sugar, and make it easier for patients to maintain a calorie deficit. However, weight loss injections should always be prescribed responsibly and used …
