Are you considering GLP-1 treatments like Wegovy for managing your weight but have questions about potential side effects? At Bolt Pharmacy, we hear concerns from many individuals about whether Wegovy can make them feel flu-like symptoms. In this article, we delve deep into answering these legitimate queries and provide comprehensive insights about GLP-1, its role in weight management and metabolic health, and its potential side effects. So, let’s demystify these uncertainties together and shed light on this vital treatment avenue for sustainable weight loss.

Can Wegovy Cause Flu-Like Symptoms?

Wegovy (semaglutide 2.4 mg) is a glucagon-like peptide-1 (GLP-1) receptor agonist licensed in the UK for weight management in adults with obesity or overweight with weight-related comorbidities. According to the Wegovy Summary of Product Characteristics (SmPC), common adverse reactions include fatigue and headache, which can contribute to feeling generally unwell, particularly during the initial weeks of treatment. While 'flu-like symptoms' is not specifically listed as a term in the SmPC, nasopharyngitis (common cold) is reported as a common side effect (affecting ≥1/100 to <1/10 patients).

It is important to distinguish between documented adverse effects and subjective experiences. The most frequently reported side effects of Wegovy are gastrointestinal in nature, including nausea (very common, ≥1/10), vomiting, diarrhoea, constipation, and abdominal pain. These occur in a substantial proportion of users and are related to the drug's mechanism of slowing gastric emptying. Systemic symptoms such as fatigue and headache are also recognised, and these may contribute to a flu-like feeling, especially when combined with reduced caloric intake and the body's adjustment to weight loss.

There is no evidence that semaglutide suppresses the immune system or directly increases susceptibility to infections. Nevertheless, the constellation of fatigue, headache, and gastrointestinal upset can mimic early flu symptoms, leading to understandable concern. If you experience these sensations, it is worth considering whether they coincide with dose escalation, dietary changes, or dehydration, all of which can exacerbate feelings of unwellness during Wegovy therapy.

Why Does Wegovy Make Some People Feel Unwell?

Understanding the pharmacology of Wegovy helps explain why some individuals feel generally unwell. Semaglutide is a GLP-1 receptor agonist that mimics the action of endogenous incretin hormones. As described in the European Medicines Agency's European Public Assessment Report (EPAR), it works by enhancing insulin secretion in a glucose-dependent manner, suppressing glucagon release, slowing gastric emptying, and reducing appetite through central nervous system pathways. These mechanisms collectively promote weight loss but also introduce physiological changes that the body must adapt to.

The slowing of gastric emptying is a key contributor to gastrointestinal side effects. When food remains in the stomach longer, patients may experience nausea, bloating, and a sense of fullness that can be uncomfortable and draining. This persistent nausea, even if mild, can lead to reduced energy levels and a general feeling of malaise. Additionally, the appetite suppression may result in significantly lower caloric intake, which may contribute to fatigue, particularly if nutritional balance is not maintained.

Headaches, reported in the SmPC as a common side effect, may be related to several factors including dehydration or reduced caloric intake. Dehydration is a particular concern, as reduced food intake often means reduced fluid intake, and gastrointestinal side effects such as vomiting or diarrhoea can further deplete fluid and electrolyte balance. The Wegovy SmPC also notes that dizziness can occur during treatment, which may be exacerbated by dehydration.

Furthermore, the dose escalation schedule for Wegovy—starting at 0.25 mg weekly and gradually increasing to the maintenance dose of 2.4 mg—is designed to improve tolerability, but each dose increase can temporarily intensify side effects, as noted in the SmPC. This stepwise approach means that feelings of unwellness may come in waves, coinciding with upward titration, which can feel reminiscent of recurrent mild viral illness.

How to Tell If Your Symptoms Are From Wegovy or Actual Flu

Distinguishing between Wegovy-related side effects and genuine influenza is important for appropriate management. According to NHS guidance, influenza is an acute viral respiratory infection characterised by sudden onset of fever (typically above 38°C), dry cough, sore throat, myalgia, headache, and profound fatigue. Respiratory symptoms are prominent, and patients often feel severely unwell with systemic features. Influenza usually peaks in winter in the UK, though the exact timing and severity vary year to year.

In contrast, Wegovy-related symptoms tend to be more insidious in onset and are often gastrointestinal-predominant. Nausea, reduced appetite, and abdominal discomfort are hallmarks of semaglutide side effects, whereas these are not typical features of influenza. Fatigue and headache can occur with both conditions, but with Wegovy, these symptoms are usually milder, more persistent, and not accompanied by high fever or respiratory signs. If you have a temperature above 38°C, productive cough, or significant respiratory symptoms, this strongly suggests an infectious cause rather than medication side effects.

Timing is also a useful clue. Wegovy-related symptoms often emerge or worsen within a few days of starting the medication or increasing the dose, and they may improve as the body adjusts. Influenza, however, develops rapidly over hours to a day or two, peaks in severity, and typically resolves within a week, though fatigue may linger.

It's also worth considering COVID-19 as a possible cause if you develop respiratory symptoms or fever, and following current NHS guidance for testing and isolation if appropriate. If you are uncertain about your symptoms, consider whether others around you are unwell with similar symptoms, which would suggest an infectious cause. Additionally, if symptoms include features not explained by Wegovy—such as significant respiratory distress, chest pain, or confusion—seek medical assessment promptly. When in doubt, contact your GP or use NHS 111 for guidance, particularly during flu season or if you have underlying health conditions that increase your risk of complications from influenza.

Managing Flu-Like Side Effects While Taking Wegovy

If you are experiencing flu-like sensations that you believe are related to Wegovy, several practical strategies can help manage these symptoms and improve your overall tolerability of the medication. Firstly, ensure adequate hydration. Drinking plenty of water throughout the day helps counteract any fluid loss from gastrointestinal side effects and can alleviate headaches and fatigue. While many people benefit from 1.5 to 2 litres daily, individual needs vary; those with heart or kidney conditions should follow their clinician's specific guidance on fluid intake.

Dietary modifications can significantly reduce nausea and discomfort. Eat smaller, more frequent meals rather than large portions, and choose bland, easily digestible foods such as toast, rice, bananas, and plain chicken. Avoid high-fat, spicy, or heavily processed foods, as these can exacerbate nausea and slow digestion further. Ginger tea or ginger biscuits may provide natural relief from nausea. It is also advisable to eat slowly and avoid lying down immediately after meals, as recommended in NHS self-care advice for nausea.

Managing fatigue involves balancing rest with gentle physical activity. Whilst it may be tempting to rest completely, light exercise such as walking can boost energy levels and support the weight loss process. Ensure you are consuming sufficient calories to meet your basic metabolic needs—severe caloric restriction can worsen fatigue and is not necessary for effective weight loss with Wegovy. A dietitian referral through your GP or weight management service can help optimise nutrition.

If headaches are troublesome, paracetamol is generally safe to use alongside Wegovy, provided you follow the recommended dosage. Non-steroidal anti-inflammatory drugs (NSAIDs) should be used with caution, particularly if you are dehydrated. Ensure you are not skipping meals, as low blood glucose can trigger headaches. If symptoms are particularly severe following a dose increase, discuss with your prescriber whether slowing the titration schedule might be appropriate. Some patients benefit from remaining at a lower dose for an additional week or two before escalating further.

Keep a symptom diary to identify patterns and triggers. This can be valuable information for your healthcare team and helps you feel more in control of your treatment. Remember that most side effects often improve over time as your body adapts to the medication.

When to Contact Your GP About Wegovy Side Effects

Whilst many side effects of Wegovy are mild and self-limiting, certain symptoms warrant prompt medical attention. You should contact your GP or NHS 111 if you experience severe, persistent vomiting or diarrhoea that prevents you from keeping down fluids, as this can lead to dehydration and electrolyte imbalance. Signs of dehydration include dizziness, reduced urine output, dark urine, dry mouth, and feeling faint when standing.

Severe abdominal pain, particularly if it is persistent and located in the upper abdomen radiating to the back, requires urgent assessment to exclude pancreatitis, a rare but serious adverse effect of GLP-1 receptor agonists identified in the Wegovy SmPC. Pancreatitis typically presents with severe, constant pain, nausea, vomiting, and feeling generally very unwell. If you suspect this, seek same-day medical evaluation.

Call 999 or go to A&E immediately for signs of an allergic reaction such as rash, swelling of the face or throat, or difficulty breathing. The same applies if you experience severe chest pain or severe breathlessness.

Changes in vision require prompt attention, particularly if you have diabetes, as semaglutide has been associated with worsening of diabetic retinopathy in some patients with type 2 diabetes, as noted in the SmPC. If you notice any new or worsening visual symptoms, arrange an urgent ophthalmic review.

Symptoms of hypoglycaemia (low blood sugar) such as sweating, dizziness, confusion, or shakiness require immediate attention, especially if you are taking insulin or sulfonylurea medications alongside Wegovy, as these combinations increase hypoglycaemia risk.

Additionally, if you develop symptoms suggestive of gallbladder disease—such as right upper abdominal pain, particularly after eating fatty foods, accompanied by nausea or jaundice—contact your GP, as rapid weight loss can increase the risk of gallstones, a warning highlighted in the MHRA safety information for GLP-1 receptor agonists.

If flu-like symptoms are accompanied by high fever, significant respiratory symptoms, chest pain, or if you feel severely unwell in a way that seems disproportionate to typical Wegovy side effects, do not assume it is medication-related. These features suggest possible infection or another medical condition requiring investigation. Patients with pre-existing conditions such as cardiovascular disease, kidney impairment, or diabetes should have a lower threshold for seeking advice.

Finally, if side effects are significantly impacting your quality of life or preventing you from continuing treatment, discuss this with your prescriber. Adjustments to the dosing schedule, additional supportive medications, or consideration of alternative weight management strategies may be appropriate. Your GP or specialist weight management service can provide individualised guidance to optimise both safety and effectiveness of your treatment journey.

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