Ozempic (semaglutide) is a once-weekly injectable medicine licensed in the UK for treating type 2 diabetes in adults. Whilst it effectively improves blood glucose control and often leads to weight loss, understanding the down side to Ozempic is essential before starting treatment. Like all medicines, Ozempic carries potential side effects and risks that vary from common gastrointestinal symptoms to rare but serious complications. This article examines the adverse effects, safety concerns, contraindications, and practical guidance on managing side effects, helping patients and healthcare professionals make informed decisions about semaglutide therapy.

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 is indicated as an adjunct to diet and exercise to improve blood glucose control, either as monotherapy when metformin is not tolerated or contraindicated, or in combination with other diabetes medicines.

Ozempic belongs to a class of drugs called glucagon-like peptide-1 (GLP-1) receptor agonists. It is administered as a once-weekly subcutaneous injection, typically starting at 0.25 mg for 4 weeks, then increasing to 0.5 mg, with further increases to 1 mg and potentially 2 mg if needed for glycaemic control.

The mechanism of action involves mimicking the naturally occurring hormone GLP-1, which plays several important roles in glucose regulation. Semaglutide works by:

• Stimulating insulin secretion from pancreatic beta cells in a glucose-dependent manner, meaning it only triggers insulin release when blood sugar levels are elevated

• Suppressing glucagon secretion, which reduces glucose production by the liver

• Slowing gastric emptying, which helps moderate the rise in blood glucose after meals

• Reducing appetite through effects on brain centres that regulate hunger and satiety

These combined actions result in improved glycaemic control and often significant weight loss, which has led to considerable interest in semaglutide beyond its licensed indication. Whilst Ozempic is approved specifically for type 2 diabetes, a higher-dose formulation called Wegovy (also semaglutide) has been licensed for weight management in certain patient groups in line with NICE guidance (TA875).

It is essential to understand that Ozempic is not licensed for weight loss alone in the UK, and its use should be under appropriate medical supervision. Patients should be aware of both the benefits and potential downsides before starting treatment.

Common Side Effects of Ozempic

Like all medicines, Ozempic can cause side effects, although not everyone experiences them. The most frequently reported adverse effects are gastrointestinal in nature and tend to occur particularly when starting treatment or increasing the dose.

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

• Nausea — often the most troublesome symptom, particularly in the first few weeks

• Diarrhoea — can range from mild to moderate in severity

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

• Vomiting — may occur alongside nausea

• Constipation — affects a significant proportion of users

• Abdominal pain or discomfort

• Decreased appetite — whilst this contributes to weight loss, some patients find it excessive

• Dyspepsia (indigestion)

• Fatigue

• Injection site reactions such as redness, itching, or bruising

These gastrointestinal symptoms typically arise because semaglutide slows gastric emptying, which is part of its therapeutic mechanism. For many patients, these effects diminish over time as the body adjusts to the medication. Starting with a lower dose and gradually titrating upwards, as recommended in the prescribing information, can help minimise these symptoms.

Hypoglycaemia (low blood sugar) is a common side effect when Ozempic is used in combination with insulin or sulfonylureas, but is uncommon when used alone. Regular blood glucose monitoring may be needed if you are taking these combinations.

Most of these side effects are mild to moderate and resolve without requiring discontinuation of treatment. However, some patients in clinical trials stopped taking semaglutide due to gastrointestinal adverse effects. It is important to discuss any persistent or troublesome symptoms with your GP or diabetes specialist nurse, as dose adjustments or supportive measures may help.

Serious Risks and Safety Concerns with Ozempic

Whilst most side effects of Ozempic are manageable, there are several serious adverse events that require careful consideration and monitoring. Healthcare professionals and patients should be aware of these potential risks.

Pancreatitis (inflammation of the pancreas) has been reported with GLP-1 receptor agonists, including semaglutide. Symptoms include severe, persistent abdominal pain that may radiate to the back, often accompanied by nausea and vomiting. If pancreatitis is suspected, Ozempic should be discontinued immediately and not restarted. Patients with a history of pancreatitis should use this medication with caution.

Diabetic retinopathy complications have been observed, particularly in patients with pre-existing diabetic eye disease and those on insulin. Rapid improvement in blood glucose control may temporarily worsen retinopathy. Patients with a history of diabetic retinopathy should be monitored appropriately with regular ophthalmology reviews, and any visual changes should be reported promptly.

Gallbladder disorders, including cholelithiasis (gallstones) and cholecystitis (gallbladder inflammation), have been reported more frequently with semaglutide than with placebo in clinical trials. This may be related to rapid weight loss. Symptoms include severe upper abdominal pain, particularly after eating fatty meals, and may require surgical intervention.

Thyroid C-cell tumours have been observed in animal studies with GLP-1 receptor agonists. While the human relevance of these findings is unknown, patients should report any neck lumps, persistent hoarseness, or difficulty swallowing.

Acute kidney injury has been reported, usually in the context of severe dehydration from gastrointestinal side effects. Patients should maintain adequate hydration, particularly if experiencing vomiting or diarrhoea.

Diabetic ketoacidosis (DKA) risk may increase if insulin doses are rapidly reduced or discontinued when starting Ozempic. The MHRA advises that insulin dose reductions should be done gradually and with careful monitoring, particularly in patients with risk factors for DKA. Symptoms of DKA include nausea, vomiting, abdominal pain, excessive thirst, rapid breathing, confusion, and unusual fatigue.

If you experience any of these serious side effects, seek medical attention promptly. Suspected adverse reactions can be reported via the MHRA Yellow Card Scheme at yellowcard.mhra.gov.uk or via the Yellow Card app.

Who Should Avoid Ozempic?

Ozempic is not suitable for everyone, and there are specific contraindications and precautions that must be considered before starting treatment.

Contraindications include:

• Hypersensitivity to semaglutide or any of the excipients

Ozempic should not be used in the following patient groups:

• Patients with type 1 diabetes mellitus — it is not a substitute for insulin

• Children and adolescents under 18 years — safety and efficacy have not been established

• Pregnant or breastfeeding women — semaglutide should be discontinued at least 2 months before a planned pregnancy, as animal studies have shown reproductive toxicity

Caution is advised in patients with:

• Severe gastrointestinal disease, including severe gastroparesis, as semaglutide delays gastric emptying

• History of pancreatitis — the risk-benefit ratio should be carefully assessed

• Diabetic retinopathy — close monitoring is required, especially in patients on insulin therapy

• Renal impairment — while no dose adjustment is required, there is limited experience in patients with severe renal impairment (eGFR <30 mL/min/1.73m²) or end-stage renal disease. Monitor renal function in patients who develop significant gastrointestinal symptoms

According to NICE guidance (NG28), GLP-1 receptor agonists like Ozempic should only be continued if there is a beneficial metabolic response, defined as a reduction in HbA1c of at least 11 mmol/mol (1.0%) and weight loss of at least 3% of initial body weight at 6 months. Patients who do not meet these criteria should have treatment reviewed and potentially discontinued.

Regular monitoring is essential, including HbA1c, weight, renal function, and in those with diabetic retinopathy, appropriate ophthalmological follow-up.

Managing Side Effects and When to Seek Medical Advice

Effective management of side effects can significantly improve tolerability and treatment adherence with Ozempic. Both patients and healthcare professionals have important roles in monitoring and responding to adverse effects.

For gastrointestinal symptoms, the following strategies may help:

• Eat smaller, more frequent meals rather than large portions

• Avoid high-fat, greasy, or spicy foods that may exacerbate nausea

• Stay well hydrated, particularly if experiencing vomiting or diarrhoea

• Take the medication at a consistent time each week, preferably when you can rest if nausea occurs

• Discuss dose titration with your healthcare provider — slowing the rate of dose increases may improve tolerance

For injection site reactions, rotate injection sites between the abdomen, thigh, and upper arm, and ensure the medication has reached room temperature before injecting.

To prevent hypoglycaemia, particularly if taking Ozempic with insulin or sulfonylureas, regular blood glucose monitoring is essential. Your doctor may need to reduce doses of these other medications. Importantly, insulin dose reductions should be made gradually to avoid the risk of diabetic ketoacidosis.

Seek urgent medical attention if you experience:

• Severe, persistent abdominal pain (possible pancreatitis or gallbladder disease)

• Signs of an allergic reaction — swelling of face, lips, tongue, or throat; difficulty breathing; severe rash

• Symptoms of dehydration — dizziness, reduced urine output, dark urine, rapid heartbeat

• Visual changes or eye pain

• Persistent vomiting preventing fluid intake

• Signs of low blood sugar — confusion, sweating, trembling, rapid heartbeat (if severe or recurrent)

• Signs of diabetic ketoacidosis — nausea, vomiting, abdominal pain, excessive thirst, rapid breathing, confusion, unusual fatigue

Contact your GP or diabetes team if:

• Gastrointestinal side effects persist beyond the first few weeks or significantly impact quality of life

• You notice a lump in your neck or experience persistent hoarseness

• You develop symptoms suggestive of gallstones (upper right abdominal pain, particularly after meals)

• You are planning pregnancy

Regular follow-up appointments are essential to monitor HbA1c, weight, renal function, and overall treatment response. The decision to continue Ozempic should be based on clinical benefit, tolerability, and alignment with NICE guidance for diabetes management.

Report any suspected side effects to the MHRA Yellow Card Scheme (yellowcard.mhra.gov.uk or via the Yellow Card app).

Frequently Asked Questions