Wegovy Side Effects: What Patients Need to Know

Around 44% of people taking Wegovy experience nausea, making it the most reported Wegovy side effect in clinical trials. That figure sounds alarming, but most cases are mild and short-lived. Knowing what to expect before you start, and how to respond when symptoms appear, makes a significant difference to whether you stay the course. This article explains the most common side effects, the less frequent but serious ones, and practical strategies for managing each.

Wegovy is a prescription-only medication. A consultation is required before starting treatment.

Common wegovy side effects and how to manage them

Gastrointestinal symptoms dominate the side effect profile. This is not a coincidence. Wegovy (semaglutide) works by mimicking GLP-1, a hormone that slows gastric emptying and suppresses appetite. The mechanism that drives weight loss is the same one that unsettles your stomach, particularly in the early weeks.

In the STEP trials, the five most commonly reported gastrointestinal side effects were:

• Nausea: 44% of Wegovy users vs 16% on placebo
• Diarrhoea: 30% vs 16%
• Vomiting: 24% vs 6%
• Constipation: 24% vs 11%
• Abdominal pain: 20% vs 14%

For most people, these symptoms appear shortly after a dose and ease within a few days. They tend to be worse during dose escalation periods and improve once the body adjusts. The standard Wegovy dosing schedule starts at 0.25 mg weekly for four weeks before gradually stepping up to the 2.4 mg maintenance dose, precisely to reduce the shock to the digestive system.

Managing nausea: Eat smaller, low-fat meals. Avoid lying down immediately after eating. Ginger tea and cold foods may help. If nausea is persistent, a GP can suggest antiemetics such as ondansetron.

Managing diarrhoea and constipation: These can affect the same person at different stages. For diarrhoea, stay hydrated and consider oral rehydration salts. Loperamide (Imodium) offers short-term relief. For constipation, increase fibre intake to 25-30 g daily, drink at least 2 litres of water, and keep moving. Docusate sodium (a stool softener) is a reasonable over-the-counter option.

Headache and fatigue: Less discussed but genuinely common. Often linked to reduced caloric intake or dehydration rather than the drug itself. Increasing water intake and ensuring adequate protein usually helps.

Less common Wegovy side effects worth monitoring

Around 5-10% of users report side effects that sit in the moderate category: dizziness, belching, bloating, heartburn, and indigestion. None are dangerous on their own, but they can affect quality of life.

Low blood sugar (hypoglycaemia): This matters specifically for people with type 2 diabetes who are also taking insulin or sulphonylureas. In that group, hypoglycaemia occurred in 6.2% of Wegovy users versus 2.5% on placebo. Symptoms include sweating, trembling, confusion, and blurred vision. Glucose tablets or gel are the first response. Anyone on diabetes medication should discuss dose adjustments with their prescriber before starting Wegovy.

Mild allergic reactions: Rash or itching at the injection site is occasionally reported. This is different from systemic anaphylaxis, which is rare but requires emergency attention (difficulty breathing, swelling of the face or throat, rapid heartbeat). If you develop hives or difficulty swallowing after an injection, seek medical help immediately.

If you are weighing up your options, it is worth reading the comparison of Mounjaro vs Wegovy to understand how the side effect profiles of the two treatments differ.

Serious Wegovy side effects: rare but important to recognise

Serious side effects are uncommon, but they exist and patients need to know the warning signs.

Thyroid tumours (boxed warning): Rodent studies showed increased thyroid tumour incidence with semaglutide. No human cases have been confirmed. However, Wegovy is contraindicated in anyone with a personal or family history of medullary thyroid carcinoma or Multiple Endocrine Neoplasia syndrome type 2 (MEN 2). Warning signs include a lump in the neck, hoarseness, or difficulty swallowing.

Pancreatitis: Rare, with five cases reported in the Wegovy arm versus one in the placebo arm across trials. Symptoms are severe upper abdominal pain, possibly radiating to the back, accompanied by nausea and fever. This requires immediate hospital assessment.

Gallstones: Rapid weight loss increases gallstone risk regardless of the method. In STEP trials, gallstones occurred in 1.6% of Wegovy users versus 0.7% on placebo, rising to 3.8% in adolescents. Symptoms include sharp upper-right abdominal pain, fever, and jaundice. Some cases require surgery.

Kidney problems: GI symptoms causing fluid loss can stress the kidneys, especially in those with pre-existing kidney disease. Dark urine, reduced urination, and swelling are warning signs. Staying well hydrated is a simple but effective preventive measure.

Mental health: Depression and suicidal ideation were reported in clinical trials and the FDA has flagged this for monitoring. Counterintuitively, a large NIH study found semaglutide users had 49-73% lower risk of suicidal ideation compared with users of other obesity and diabetes medications. Pre-treatment mental health screening is nonetheless recommended, and any deterioration in mood during treatment should be reported promptly.

Who should not take Wegovy

To meet NHS eligibility criteria for GLP-1 weight loss treatment, patients typically need a BMI of 35 or above with at least one weight-related health condition, or a BMI of 40 or above. Wegovy is not suitable for people who are pregnant, breastfeeding, or planning pregnancy within two months of stopping. It should not be used by anyone with a history of MEN 2, medullary thyroid carcinoma, or active pancreatitis.

For a broader overview of injectable and oral weight loss options, see our guide to weight loss treatments.

FAQs

How long do wegovy side effects last?

Most gastrointestinal side effects are at their worst during the first four to eight weeks of treatment and during each dose escalation. The majority resolve within two to four weeks of reaching a stable dose. Around 5-10% of users discontinue treatment due to persistent GI symptoms.

Can wegovy side effects be avoided completely?

Not always, but they can be reduced. Following the gradual dosing schedule, eating smaller low-fat meals, staying hydrated, and avoiding alcohol during the adjustment period all lower the risk of severe symptoms. Some people have no side effects at all.

Is nausea worse on higher doses of Wegovy?

Yes. Nausea is most common when the dose increases, which happens every four weeks under the standard schedule. At the 2.4 mg maintenance dose, many users have already adapted and find symptoms more manageable than in the early weeks.

When should I contact a doctor about wegovy side effects?

Contact your prescriber if side effects are severe, persistent, or affecting your ability to eat and drink. Seek emergency care for chest pain, severe abdominal pain, signs of an allergic reaction, or any difficulty breathing.