Ozempic Thyroid Cancer: UK Evidence and Risk

Ozempic thyroid cancer concerns have prompted questions from patients and clinicians since preclinical rodent studies linked GLP-1 receptor agonists to thyroid C-cell changes. Ozempic (semaglutide) is MHRA-authorised for type 2 diabetes in adults, and while animal data raised an early signal, current regulatory assessments by the EMA and MHRA have not established a causal link to thyroid cancer in humans. This article explains what the evidence actually shows, who should exercise caution, which symptoms to watch for, and how to have an informed conversation with your GP or specialist about your personal risk.

Does Ozempic increase the risk of thyroid cancer?

Current evidence does not confirm that Ozempic causes thyroid cancer in humans; rodent findings are considered of uncertain relevance to humans, and the UK SmPC includes precautionary counselling rather than a contraindication.

Current evidence does not establish that Ozempic (semaglutide) causes thyroid cancer in humans, though the question remains an active area of pharmacovigilance. Ozempic is a glucagon-like peptide-1 (GLP-1) receptor agonist, authorised by the MHRA for the treatment of type 2 diabetes in adults.^[1][2] It is a different product from Wegovy, which contains semaglutide at a higher dose and is licensed for weight management.^[4][5] Ozempic works by mimicking the action of the naturally occurring GLP-1 hormone, stimulating insulin release, suppressing glucagon, and slowing gastric emptying.

The concern about thyroid cancer arose from preclinical studies in rodents, where GLP-1 receptor agonists were associated with C-cell hyperplasia and medullary thyroid carcinoma (MTC).^[6][7] Regulatory assessments by the EMA and MHRA, including the EMA's European Public Assessment Report (EPAR) for semaglutide, note that rodent thyroid C-cells express GLP-1 receptors at considerably higher density than human C-cells, and that the relevance of these animal findings to humans is considered uncertain.^[7][8] The UK Summary of Product Characteristics (SmPC) for Ozempic (section 4.4) advises that patients should be informed about the symptoms of thyroid tumours as a precautionary measure, and that cases of thyroid neoplasm have been reported in clinical trials, though a causal relationship has not been established.

The UK SmPC does not list medullary thyroid carcinoma or multiple endocrine neoplasia type 2 (MEN2) as contraindications; these restrictions appear in US labelling but do not form part of the UK authorisation. Patients should not assume that US prescribing information applies to their treatment in the United Kingdom.

The absence of a confirmed causal link does not mean the question is closed. Ongoing post-marketing surveillance continues to monitor this signal, and patients with specific personal or family histories should discuss their individual circumstances with a clinician before starting or continuing treatment.

What does the evidence from human studies actually show?

Large observational studies and clinical trial data have not demonstrated a robust causal link between semaglutide and thyroid cancer; the EMA's PRAC concluded the evidence does not support causation, while recommending continued monitoring.

Large observational studies and clinical trial data in humans have not demonstrated a statistically robust causal association between semaglutide use and thyroid cancer. Several epidemiological studies, including analyses of real-world healthcare databases, have examined rates of thyroid cancer among GLP-1 receptor agonist users compared with people taking other diabetes medicines. Results have been mixed, with some studies suggesting a modest signal and others finding no significant difference after adjusting for confounding factors such as obesity, which is itself associated with an increased risk of certain cancers.

A notable large-scale study published in Nature Medicine in 2023 (Bezin et al., using French national health insurance data) reported a potential association between GLP-1 receptor agonist use and thyroid cancer, including papillary thyroid cancer, over a median follow-up of around four years. The authors acknowledged important limitations, including the observational design, the inability to fully control for all confounders, and the relatively short follow-up periods involved. Papillary thyroid cancer is biologically distinct from medullary thyroid cancer, the type identified in rodent studies, which adds further complexity to interpreting these findings.

At present, no randomised controlled trial has been powered or designed to detect a thyroid cancer outcome as a primary endpoint. The overall absolute numbers of thyroid cancer cases in clinical trials of semaglutide have been low. The EMA's Pharmacovigilance Risk Assessment Committee (PRAC) has reviewed available data on GLP-1 receptor agonists and thyroid cancer signals and concluded that the evidence does not support a causal relationship in humans, while acknowledging that continued monitoring is warranted given the biological plausibility raised by animal data.^[9] Patients and clinicians should interpret these findings with appropriate caution, recognising that observational data can identify signals but cannot confirm causation.

Who should avoid Ozempic because of thyroid concerns?

The only UK contraindication for Ozempic is hypersensitivity to semaglutide; MTC and MEN2 are not UK contraindications, though patients with a personal or family history of these conditions should discuss individual risk with a specialist.

The UK SmPC for Ozempic (section 4.3) lists hypersensitivity to semaglutide or any of its excipients as the only contraindication. There is no UK contraindication specifically for medullary thyroid carcinoma or multiple endocrine neoplasia type 2; these are restrictions found in US labelling but do not apply under the UK authorisation.

Nevertheless, the UK SmPC (section 4.4) advises that prescribers should inform patients about the symptoms that may be associated with thyroid tumours, such as a lump or swelling in the neck, difficulty swallowing, persistent hoarseness, or shortness of breath. This precautionary advice is particularly relevant for patients who have a personal or family history of thyroid disease, including benign thyroid nodules or prior thyroid surgery; such individuals may benefit from a more detailed discussion of their individual risk profile with their clinician, though this reflects clinical judgement rather than a specific SmPC requirement. A personal or family history of MTC or MEN2 is not a UK contraindication but warrants an individualised discussion with a specialist before starting treatment.

The UK SmPC does not recommend routine thyroid function testing or calcitonin measurement as a screening measure before or during Ozempic treatment.^[1] If a patient has pre-existing thyroid disease that is already being managed, their endocrinologist or GP should be made aware that they are starting or taking Ozempic, so that any monitoring plan can be reviewed accordingly.

The UK SmPC (section 4.6) states that Ozempic is not recommended during pregnancy or breastfeeding. Women of childbearing potential should use effective contraception during treatment. The SmPC advises that Ozempic should be discontinued at least two months before a planned pregnancy, given its long half-life; patients planning a pregnancy should discuss the timing of discontinuation with their prescriber.

What side effects should you watch for and when to seek help?

Common side effects are gastrointestinal; for thyroid safety, report any new neck lump, persistent hoarseness, difficulty swallowing, or neck pain to your GP promptly rather than waiting for a routine appointment.

The most commonly reported side effects of Ozempic are gastrointestinal in nature, including nausea, vomiting, diarrhoea, constipation, and abdominal discomfort, particularly during dose escalation (UK SmPC section 4.^[1][12]8). These effects are generally transient and tend to improve as the body adjusts to the medication. Eating smaller meals, avoiding high-fat foods, and staying well hydrated can help manage these symptoms.

In relation to thyroid safety specifically, patients taking Ozempic should be alert to the following symptoms and report them promptly to their GP:

• A new or growing lump or swelling in the neck

• Persistent hoarseness or a change in voice that does not resolve

• Difficulty swallowing or breathing

• Persistent neck pain

These symptoms do not necessarily indicate thyroid cancer, as they can have many other causes, but they warrant prompt clinical assessment. Patients should contact their GP if they notice any of these changes and should not wait for a routine appointment if symptoms are new or worsening.

Acute pancreatitis has been reported in association with GLP-1 receptor agonists, including post-marketing reports of necrotising pancreatitis and reports with a fatal outcome (UK SmPC section 4.4). Persistent severe abdominal pain, which may radiate to the back, should be assessed urgently. Patients experiencing this symptom should seek same-day medical advice by contacting their GP or calling NHS 111. If symptoms are severe and accompanied by collapse or inability to function, they should attend an accident and emergency department or call 999.

Suspected side effects from Ozempic can be reported to the MHRA via the Yellow Card scheme at yellowcard.mhra.gov.uk.

What has the MHRA said about Ozempic and thyroid safety?

The MHRA has not concluded that Ozempic causes thyroid cancer; the EMA's PRAC reviewed available data and found no causal relationship, though ongoing pharmacovigilance monitoring continues.

The MHRA has not issued a specific Drug Safety Update concluding that Ozempic causes thyroid cancer in humans, but thyroid safety remains a monitored area under the ongoing pharmacovigilance obligations that apply to all authorised medicines. The MHRA works closely with the EMA to review emerging post-marketing data, and any new safety signals identified through spontaneous reporting, published literature, or periodic safety update reports are assessed through established regulatory processes.

The EMA's PRAC has reviewed data on GLP-1 receptor agonists and thyroid cancer signals, including the French observational study published in Nature Medicine in 2023. Following its review, the PRAC concluded that the available evidence did not support a causal relationship between GLP-1 receptor agonist use and thyroid cancer in humans, though it acknowledged that continued monitoring was warranted given the biological plausibility raised by animal data. The EMA EPAR for Ozempic reflects this position.

The UK SmPC for Ozempic reflects this regulatory stance by including precautionary counselling advice on thyroid tumour symptoms (section 4.4) without listing thyroid malignancy as a contraindication. The regulatory position may evolve as longer-term post-marketing data accumulate, and prescribers should ensure they are working from the most current version of the SmPC, which is available through the electronic Medicines Compendium (emc) at medicines.org.uk.

Talking to your GP or specialist about your personal risk

Your GP or specialist is best placed to weigh Ozempic's benefits and risks against your personal and family medical history, existing thyroid conditions, and current diabetes management needs.

A conversation with your GP or specialist is the most appropriate way to assess your personal risk profile before starting or continuing Ozempic. Individual risk depends on a range of factors, including your personal and family medical history, the presence of any pre-existing thyroid conditions, your current glycaemic control, and whether alternative treatments for type 2 diabetes may be equally suitable for you. No single piece of published evidence applies uniformly to every patient, and a clinician who knows your full history is best placed to weigh the benefits and risks in your specific case.

When preparing for this conversation, it may be helpful to note:

• Any personal history of thyroid disease, thyroid nodules, or thyroid surgery

• Any family history of thyroid cancer or endocrine conditions

• Any neck symptoms you have noticed, even if mild

• Other medicines you are taking, including supplements

• Whether you are pregnant, planning a pregnancy, or breastfeeding

NICE guideline NG28 (Type 2 diabetes in adults: management) supports shared decision-making in the management of type 2 diabetes, and you are entitled to ask questions about the evidence base for any treatment recommended to you.^[15]

For patients accessing diabetes or weight-management treatment through online services, Bolt Pharmacy is a GPhC-registered UK online pharmacy offering online consultations with prescriber review and pharmacist support. You can verify a pharmacy's registration with the GPhC (which regulates pharmacy premises in Great Britain) at pharmacyregulation.org, or with the PSNI if you are in Northern Ireland. Ozempic is one option a prescriber may consider following a full clinical assessment, and is only prescribed where clinically appropriate.

If your GP refers you to an endocrinologist or diabetes specialist, bring a list of your current medicines and any relevant test results. If your circumstances change, for example if you develop new symptoms or a family member receives a thyroid diagnosis, inform your prescriber promptly so that your treatment plan can be reviewed.

Scientific References

1. Ozempic 0.5 mg solution for injection in pre-filled pen – Summary of Product Characteristics.
2. MHRA warns of unsafe fake weight loss pens.
3. Ozempic – European Public Assessment Report.
4. First GLP-1 tablet for weight loss approved in the UK.
5. Medicines regulator approves up to 7.2mg dose of semaglutide (Wegovy) for patients with obesity only.
6. Glucagon-like Peptide-1 Receptor Agonists and Thyroid Cancer: Review of Preclinical and Human Data.
7. Wegovy – EPAR Product Information (semaglutide).
8. Semaglutide s.c. and oral semaglutide – Wegovy Risk Management Plan.
9. Meeting highlights from the Pharmacovigilance Risk Assessment Committee (PRAC), 23–26 October 2023.
10. GLP-1 Receptor Agonists and the Risk of Thyroid Cancer (Bezin et al.).
11. GLP-1 receptor agonists and dual GLP-1/GIP receptor agonists: strengthened warnings on acute pancreatitis including necrotising and fatal cases.
12. GLP-1 receptor agonists: reminder of the potential side effects and to be aware of the potential for misuse.
13. GLP-1 medicines for weight loss and diabetes: what you need to know.
14. Semaglutide: a medicine to manage type 2 diabetes or obesity.
15. Type 2 diabetes in adults: management. Guideline NG28.
16. The Yellow Card scheme: guidance for healthcare professionals, patients and the public.

Frequently Asked Questions