Wegovy (semaglutide 2.4mg) is approved in the UK for weight management in adults with obesity or overweight with weight-related health conditions. Like all medications, it carries a risk of side effects — most of which are gastrointestinal and tend to improve as your body adjusts to the treatment.
The following side effects were reported in more than 1 in 10 people (very common) in clinical trials:
- Nausea — the most commonly reported side effect, particularly during dose escalation
- Diarrhoea — often occurs in the first few weeks at each new dose
- Vomiting — less common than nausea but reported by around 25% of users
- Constipation — particularly at higher doses
- Abdominal pain — cramping or discomfort, usually mild
- Headache — reported by around 14% of users in STEP trials
Most GI side effects are worst during dose escalation and improve significantly once you reach a stable dose. Eating smaller meals, avoiding fatty foods, and staying hydrated can help manage symptoms.
The following are less common but require immediate medical attention:
- Pancreatitis — severe, persistent abdominal pain radiating to the back; stop treatment and seek emergency care
- Gallbladder problems — rapid weight loss can increase gallstone risk; report right-sided abdominal pain
- Diabetic retinopathy — worsening eye symptoms in people with type 2 diabetes
- Severe allergic reaction — rash, swelling, difficulty breathing; seek emergency care immediately
- Thyroid tumours — a theoretical risk based on animal studies; report any neck lump or difficulty swallowing
- Kidney problems — dehydration from vomiting/diarrhoea can worsen kidney function
| Dose | Nausea Risk | Vomiting Risk | Notes |
|---|---|---|---|
| 0.25mg (weeks 1–4) | Moderate | Low | Starting dose — most people tolerate well |
| 0.5mg (weeks 5–8) | Moderate–High | Moderate | First escalation — GI effects often peak here |
| 1mg (weeks 9–12) | Moderate | Moderate | Symptoms usually improving by this point |
| 1.7mg (weeks 13–16) | Moderate | Low–Moderate | Second escalation — some people stay at 1mg |
| 2.4mg (maintenance) | Low–Moderate | Low | Most people well-adapted by maintenance dose |
- Eat smaller, more frequent meals rather than large portions
- Avoid high-fat, greasy, or spicy foods — these worsen nausea
- Stay well hydrated, especially if experiencing vomiting or diarrhoea
- Inject on the same day each week and consider timing (some people prefer evening injections so nausea occurs during sleep)
- Don't rush dose escalation — if side effects are severe, stay at your current dose for an extra 4 weeks
- Ginger tea, small crackers, and anti-nausea wristbands can help with mild nausea
Both Wegovy and Mounjaro share a similar GI side effect profile. Mounjaro may cause slightly more constipation at higher doses, while Wegovy may cause slightly more nausea at the 0.5mg escalation step. Overall, the tolerability profiles are broadly comparable.
Wegovy is not suitable for people with a personal or family history of medullary thyroid carcinoma (MTC) or Multiple Endocrine Neoplasia syndrome type 2 (MEN 2). Always disclose your full medical history to your prescriber.