Wegovy side effects: a doctor's guide to what to expect

The most frequently reported side effects of Wegovy are gastrointestinal in nature.

Clinical trials (the STEP programme) showed that these affect a significant proportion of patients, particularly during the dose escalation phase.

Very common side effects (affecting more than 1 in 10 people):

• Nausea: the most reported side effect, affecting up to 44 per cent of patients in trials. It is usually worst during the first few weeks at each new dose level
• Diarrhoea: affects approximately 30 per cent of patients and tends to be intermittent
• Constipation: reported by around 24 per cent of patients
• Vomiting: occurs in approximately 25 per cent of patients, most commonly during dose escalation

Common side effects (affecting up to 1 in 10 people):

• Abdominal pain and bloating: related to the delayed gastric emptying caused by semaglutide
• Headaches: usually mild and self-limiting
• Fatigue: often linked to reduced calorie intake
• Dizziness: particularly during the early weeks of treatment
• Injection site reactions: redness, swelling, or itching at the injection site

These side effects are a direct consequence of how semaglutide works.

By activating GLP-1 receptors, Wegovy slows gastric emptying and reduces appetite, which accounts for the gastrointestinal symptoms.

Following the recommended dose escalation schedule is the most effective way to reduce the severity of these effects.

Although uncommon, there are several serious side effects associated with Wegovy that require prompt medical attention. The MHRA and BNF highlight the following risks.

Pancreatitis:

Acute pancreatitis has been reported in patients taking GLP-1 receptor agonists.

Symptoms include severe, persistent pain in the upper abdomen, often radiating to the back, accompanied by nausea and vomiting.

If pancreatitis is suspected, Wegovy should be stopped immediately and not restarted.

Gallbladder disease:

Rapid weight loss increases the risk of gallstones. The STEP trials reported a higher rate of gallbladder-related events in patients taking semaglutide compared to placebo.

Symptoms include sudden, intense pain in the upper right abdomen, nausea, and vomiting.

Acute kidney injury:

Severe gastrointestinal side effects (persistent vomiting or diarrhoea) can lead to dehydration and subsequent kidney damage.

Patients should maintain adequate fluid intake and seek medical advice if they cannot keep fluids down.

Thyroid tumours:

In animal studies, semaglutide caused thyroid C-cell tumours.

Although this has not been confirmed in humans, Wegovy is contraindicated in patients with a personal or family history of medullary thyroid carcinoma or multiple endocrine neoplasia syndrome type 2.

Suicidal ideation:

The MHRA has issued advice for healthcare professionals to be vigilant for signs of suicidal thoughts or self-harm in patients taking GLP-1 receptor agonists.

Patients should report any changes in mood to their prescriber.

Nausea is the most common reason patients consider stopping Wegovy. However, there are several evidence-based strategies that can help you manage these symptoms effectively.

Dietary adjustments:

• Eat smaller, more frequent meals rather than three large ones
• Avoid fatty, greasy, or heavily spiced foods
• Eat slowly and chew your food thoroughly
• Stop eating when you feel full, even if the portion seems small
• Avoid lying down immediately after eating

Hydration:

• Sip water throughout the day rather than drinking large amounts at once
• Ginger tea or peppermint tea may help settle the stomach
• If vomiting or diarrhoea is persistent, consider oral rehydration sachets

Timing and lifestyle:

• Take your injection at a consistent time each week
• Some patients find that injecting in the evening helps them sleep through the worst of the nausea
• Light physical activity such as walking can aid digestion

When to seek help:

• If nausea prevents you from eating or drinking for more than 24 hours
• If vomiting is severe or persistent
• If you notice signs of dehydration such as dark urine, dizziness, or a dry mouth

Your prescriber may consider slowing the dose escalation or temporarily reducing the dose if symptoms are particularly severe.

One of the most reassuring aspects of Wegovy treatment is that side effects tend to follow a predictable pattern, becoming less troublesome as your body adapts.

During dose escalation (weeks 1 to 16):

• This is when side effects are most pronounced
• Nausea and vomiting typically peak within the first week at each new dose level
• The escalation schedule is designed to minimise these effects by increasing the dose gradually over 16 weeks

At maintenance dose (2.4 mg):

• Most patients report a significant reduction in gastrointestinal symptoms by the time they reach the maintenance dose
• In the STEP 1 trial, nausea rates dropped considerably after the first 20 weeks
• Some patients continue to experience mild symptoms, but these are generally manageable

Long-term use:

• Data from extension studies suggest that side effects remain stable or improve further over time
• New side effects developing after months of stable treatment are uncommon and should be reported to your doctor
• The weight loss benefits of Wegovy are sustained with continued use

If you are struggling with side effects during the escalation phase, remember that persisting through this period usually leads to better tolerance.

Your doctor can advise on whether to pause at a lower dose for an extra few weeks before increasing.

While most Wegovy side effects are manageable at home, certain symptoms require prompt medical assessment.

Contact your prescriber if you experience:

• Persistent nausea or vomiting that prevents adequate food and fluid intake
• Changes in mood, thoughts of self-harm, or suicidal ideation
• Symptoms of gallbladder problems such as pain in the upper right abdomen
• Injection site reactions that worsen or do not resolve
• Any side effects that significantly affect your quality of life

Seek urgent medical attention (call 999 or go to A&E) if you notice:

• Severe abdominal pain that could indicate pancreatitis
• Symptoms of a severe allergic reaction: widespread rash, swelling of the face or throat, difficulty breathing
• Signs of severe dehydration: confusion, very dark urine, rapid heartbeat
• A lump or swelling in your neck (possible thyroid concern)

The NHS weight management service and your prescribing team are there to support you throughout your treatment.

Regular follow-up appointments help ensure that any side effects are identified early and managed appropriately.