Ozempic (semaglutide) is a once-weekly injectable medicine licensed in the UK for managing type 2 diabetes in adults. Whilst it effectively lowers blood glucose and may support weight reduction, understanding the health concerns with Ozempic is essential for safe use. Common side effects include nausea, vomiting, and diarrhoea, whilst rarer but serious risks involve pancreatitis, gallbladder disease, and diabetic retinopathy complications. This article examines the mechanism of action, common and serious adverse effects, contraindications, and practical strategies for monitoring and managing side effects. Patients should always discuss potential risks and benefits with their GP or diabetes specialist before starting treatment.

What Is Ozempic and How Does It Work?

Ozempic (semaglutide) is a prescription medicine licensed in the UK for the treatment of type 2 diabetes mellitus in adults. It belongs to a class of drugs known as glucagon-like peptide-1 (GLP-1) receptor agonists. Ozempic is administered as a once-weekly subcutaneous injection on the same day each week and is available in pre-filled pens at doses of 0.25 mg, 0.5 mg, 1 mg, and 2 mg. The Medicines and Healthcare products Regulatory Agency (MHRA) has approved Ozempic specifically for glycaemic control in adults with type 2 diabetes, either as monotherapy when metformin is inappropriate or in combination with other glucose-lowering medicines.

The mechanism of action of Ozempic centres on mimicking the naturally occurring hormone GLP-1, which is released by the intestine in response to food intake. Semaglutide binds to GLP-1 receptors in the pancreas, stimulating insulin secretion in a glucose-dependent manner—meaning insulin is released only when blood glucose levels are elevated. Simultaneously, it suppresses the release of glucagon, a hormone that raises blood sugar. This dual action helps to lower blood glucose levels without causing excessive hypoglycaemia when used alone.

Beyond its effects on insulin and glucagon, Ozempic also slows gastric emptying, which delays the absorption of nutrients and prolongs the sensation of fullness after eating. This mechanism contributes to reduced appetite and can lead to weight loss, an effect that has attracted considerable attention. Additionally, semaglutide acts on receptors in the brain that regulate appetite and food intake. While weight reduction is a beneficial side effect for many patients with type 2 diabetes, it is important to note that in the UK, Ozempic is not licensed for weight management alone—Wegovy (a higher-dose semaglutide formulation) is the approved product for chronic weight management in specific patient groups according to NICE guidance.

Common Side Effects and Health Concerns with Ozempic

Like all medicines, Ozempic can cause side effects, although not everyone will experience them. The most frequently reported adverse effects are gastrointestinal in nature and are generally mild to moderate in severity. According to the UK product information, nausea is very common (affecting more than 1 in 10 people), particularly when starting treatment or increasing the dose. Other common side effects (affecting up to 1 in 10 people) include vomiting, diarrhoea, abdominal pain, and constipation. These symptoms typically improve over time as the body adjusts to the medication, usually within a few weeks.

Other common side effects include:

• Decreased appetite: While this can support weight loss, some patients may find it excessive or uncomfortable.

• Dyspepsia and gastro-oesophageal reflux: Heartburn and indigestion may occur due to delayed gastric emptying.

• Injection site reactions: Redness, itching, or swelling at the injection site are usually mild and transient.

• Fatigue and dizziness: Some patients report feeling unusually tired or light-headed, particularly in the early stages of treatment.

Hypoglycaemia (low blood sugar) is uncommon with Ozempic when used alone, as its glucose-lowering effect is glucose-dependent. However, the risk increases significantly when Ozempic is combined with other diabetes medications, particularly sulphonylureas (such as gliclazide) or insulin. Symptoms of hypoglycaemia include sweating, trembling, confusion, palpitations, and hunger. Patients should be educated on recognising and managing low blood sugar episodes.

Gallbladder problems including gallstones and inflammation of the gallbladder (cholecystitis) have been reported. Symptoms include severe pain in the upper right abdomen, fever, or yellowing of the skin or eyes. If you experience these symptoms, seek urgent medical attention.

If gastrointestinal side effects are severe or persistent, dose adjustments or alternative treatments may be considered. Staying well-hydrated is important, especially if experiencing vomiting or diarrhoea. Patients should not stop Ozempic without consulting their GP or diabetes specialist, except in cases of suspected serious adverse reactions such as pancreatitis or severe allergic reactions.

You can report any suspected side effects to the MHRA Yellow Card Scheme at yellowcard.mhra.gov.uk.

Serious Risks and When to Seek Medical Attention

Although uncommon, Ozempic is associated with several serious adverse effects that require prompt medical attention. One of the most significant concerns is acute pancreatitis (inflammation of the pancreas). Symptoms include severe, persistent abdominal pain that may radiate to the back, often accompanied by nausea and vomiting. Pancreatitis has been reported in clinical trials and post-marketing surveillance of GLP-1 receptor agonists. If you experience sudden, severe stomach pain, you should stop taking Ozempic immediately and seek urgent medical advice.

Diabetic retinopathy complications have also been observed, particularly in patients with pre-existing diabetic eye disease. Rapid improvements in blood glucose control may temporarily worsen retinopathy. The SUSTAIN-6 trial identified a higher incidence of retinopathy complications in patients treated with semaglutide compared to placebo, especially in those with a history of retinopathy. Regular eye examinations are essential for all patients with diabetes, and any sudden changes in vision—such as blurred vision, floaters, or visual loss—should be reported to a healthcare professional urgently.

Acute gallbladder disease, including gallstones (cholelithiasis) and inflammation of the gallbladder (cholecystitis), has been reported in patients taking GLP-1 receptor agonists. Symptoms include severe pain in the upper right abdomen that may radiate to the shoulder, fever, nausea, vomiting, and jaundice (yellowing of the skin or eyes). These conditions require immediate medical attention.

Acute kidney injury and worsening of chronic kidney disease have been reported, often in association with severe gastrointestinal side effects leading to dehydration. Patients should maintain adequate hydration, particularly if experiencing vomiting or diarrhoea. Warning signs include reduced urine output, swelling of the ankles or feet, and unusual fatigue.

Animal studies have shown that semaglutide caused thyroid C-cell tumours in rodents. The relevance of these findings to humans is unknown. The UK product information does not contraindicate use in patients with a personal or family history of medullary thyroid carcinoma, but patients should report any neck lump, persistent hoarseness, or difficulty swallowing.

Severe allergic reactions (anaphylaxis) are rare but possible. Symptoms include difficulty breathing, swelling of the face or throat, rapid heartbeat, and severe rash. This constitutes a medical emergency requiring immediate attention. If you experience any of these serious symptoms, contact your GP, call NHS 111, or go to A&E as appropriate.

Who Should Avoid Ozempic? Contraindications and Precautions

Ozempic is not suitable for everyone, and certain patient groups should avoid this medication. According to the UK product information, Ozempic is contraindicated in individuals with:

• Hypersensitivity to semaglutide or any of the excipients in the formulation.

Ozempic is not licensed for use in type 1 diabetes or for the treatment of diabetic ketoacidosis. It should not be used in children or adolescents under 18 years of age, as safety and efficacy have not been established in this population.

Special precautions are necessary in several clinical scenarios. Ozempic is not recommended in patients with severe gastrointestinal disease, including severe gastroparesis (delayed stomach emptying), as it further slows gastric emptying and may exacerbate symptoms. Those with a history of pancreatitis require careful consideration, and alternative treatments may be preferable.

The delayed gastric emptying caused by Ozempic may affect the absorption of concomitant oral medications. This is particularly important for medicines with a narrow therapeutic index or those requiring rapid clinical effect. Additional monitoring may be needed when starting or stopping Ozempic in patients taking such medications.

In patients with renal impairment, dose adjustment is not routinely required, but caution is advised in those with severe renal impairment or end-stage renal disease, as clinical experience is limited. Dehydration from gastrointestinal side effects can precipitate acute kidney injury, so maintaining hydration is crucial.

Pregnancy and breastfeeding: Ozempic should be discontinued at least two months before a planned pregnancy, as there is insufficient data on its safety during pregnancy. Animal studies have shown reproductive toxicity. If pregnancy occurs during treatment, Ozempic should be stopped immediately. It is not known whether semaglutide passes into breast milk, so breastfeeding is not recommended while using this medication.

Patients with diabetic retinopathy should be monitored closely, particularly if they have a history of proliferative retinopathy or maculopathy. Elderly patients (over 75 years) have limited clinical data, and treatment should be initiated cautiously. Before starting Ozempic, a thorough medical history and discussion of potential risks and benefits with a healthcare professional is essential.

Managing Side Effects and Monitoring Your Health on Ozempic

Effective management of side effects and appropriate monitoring are key to safe and successful treatment with Ozempic. Gastrointestinal symptoms, the most common adverse effects, can often be minimised through practical strategies. Eating smaller, more frequent meals rather than large portions can help reduce nausea and bloating. Avoiding fatty, fried, or spicy foods may also alleviate discomfort. Staying well-hydrated is important, particularly if experiencing vomiting or diarrhoea. If nausea is severe, your GP may recommend anti-emetic medication or a slower dose escalation schedule.

The standard dosing regimen begins with 0.25 mg once weekly for four weeks, primarily to improve tolerability rather than for glycaemic control. The dose is then increased to 0.5 mg weekly, with further increases to 1 mg or 2 mg if additional glucose control is needed. Gradual dose titration significantly reduces the likelihood of gastrointestinal side effects. Ozempic should be administered on the same day each week, at any time of day, with or without food.

If you miss a dose, take it as soon as possible within 5 days after the missed dose. If more than 5 days have passed, skip the missed dose and take your next dose on the regularly scheduled day.

Regular monitoring is essential throughout treatment. This includes:

• HbA1c testing every 3–6 months to assess glycaemic control.

• Renal function tests (serum creatinine and eGFR), particularly in patients at risk of dehydration or with pre-existing kidney disease.

• Annual eye examinations by an optometrist or ophthalmologist, with more frequent screening if diabetic retinopathy is present.

• Blood pressure and lipid profile monitoring, as cardiovascular risk factor management remains a priority in diabetes care.

Patients should be educated on recognising hypoglycaemia, especially if taking Ozempic alongside sulphonylureas or insulin. Carrying fast-acting carbohydrates (glucose tablets, sugary drinks) and knowing how to treat low blood sugar is important. When starting Ozempic, your doctor may reduce the dose of sulphonylureas or insulin to lower the risk of hypoglycaemia.

Injection technique should be reviewed regularly. Ozempic can be injected into the abdomen, thigh, or upper arm, and injection sites should be rotated to prevent lipodystrophy. The pen should be stored in the refrigerator before first use (do not freeze) and can then be kept at room temperature (below 30°C) for up to six weeks. Keep the pen cap on when not in use to protect from light.

If side effects become intolerable or if there are concerns about the medication's effectiveness, patients should consult their GP or diabetes specialist nurse. Treatment plans can be adjusted, and alternative medications are available. NICE guidance emphasises individualised treatment approaches in type 2 diabetes, taking into account patient preferences, comorbidities, and tolerability. Open communication with your healthcare team ensures that Ozempic therapy is both safe and effective for your individual circumstances.

Frequently Asked Questions