Victoza (liraglutide) is a GLP-1 receptor agonist licensed in the UK for type 2 diabetes mellitus. Concerns about a potential link between Victoza and medullary thyroid carcinoma (MTC) arose from animal studies showing thyroid C-cell tumours in rodents. However, determining how many people have developed thyroid cancer from Victoza remains challenging, as no definitive causal relationship has been established in humans. The MHRA and EMA have reviewed available evidence and concluded that whilst the risk cannot be entirely excluded, there is insufficient evidence to confirm a direct link. This article examines the clinical evidence, regulatory guidance, and what UK patients should know.
Quick Answer: No definitive number exists, as no causal relationship between Victoza and thyroid cancer has been established in humans despite theoretical concerns from animal studies.
Victoza (liraglutide) is a glucagon-like peptide-1 (GLP-1) receptor agonist licensed in the UK for treating type 2 diabetes mellitus. For weight management, liraglutide is marketed under a different brand name (Saxenda) at a higher dose. Since its approval, concerns have been raised about a potential association between liraglutide and thyroid C-cell tumours, specifically medullary thyroid carcinoma (MTC).
The theoretical link stems from preclinical animal studies conducted during drug development. In rodent models, liraglutide was associated with an increased incidence of thyroid C-cell tumours, including adenomas and carcinomas, at clinically relevant exposures. These C-cells produce calcitonin, and GLP-1 receptors are present on rodent thyroid C-cells, providing a biological mechanism. However, the relevance of these findings to humans remains uncertain, as human thyroid C-cells express GLP-1 receptors at much lower levels than rodents.
It is crucial to understand that no definitive causal relationship has been established between Victoza use and thyroid cancer in humans. The Medicines and Healthcare products Regulatory Agency (MHRA) and the European Medicines Agency (EMA) have reviewed available evidence and concluded that whilst the risk cannot be entirely excluded, there is insufficient evidence to confirm a direct link. The UK Summary of Product Characteristics (SmPC) includes special warnings and precautions regarding thyroid disease, advising that patients with thyroid disease should be monitored and counselled about the potential risk.
Patients prescribed Victoza should be informed about this theoretical risk and the importance of reporting any unusual neck symptoms, such as persistent lumps, hoarseness, or difficulty swallowing, to their GP promptly. Routine monitoring with calcitonin or thyroid ultrasound is not recommended in the general population taking Victoza, as this has not been proven beneficial.
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Start HereDetermining the exact number of people who have developed thyroid cancer whilst taking Victoza is challenging due to the rarity of medullary thyroid carcinoma and the complexities of establishing causation. MTC accounts for only 3–5% of all thyroid cancers, with an annual incidence of approximately 0.2–0.4 cases per 100,000 people in the general population.
Large-scale clinical trials conducted before and after Victoza's approval have not demonstrated a statistically significant increase in thyroid cancer cases among users. The LEADER trial (published in the New England Journal of Medicine, 2016), a cardiovascular outcomes study involving over 9,000 patients with type 2 diabetes followed for a median of 3.8 years, reported thyroid neoplasms in both treatment groups. However, the numbers were too small to draw definitive conclusions, and the difference was not statistically significant. Similar cardiovascular outcome trials with other GLP-1 receptor agonists (SUSTAIN-6 with semaglutide, REWIND with dulaglutide) have not shown a consistent signal for increased thyroid cancer risk.
Post-marketing surveillance data from regulatory authorities, including the MHRA's Yellow Card scheme, have recorded spontaneous reports of thyroid cancer in patients taking Victoza. However, spontaneous reporting systems have inherent limitations: they cannot establish causation, may be subject to reporting bias, and lack denominator data (the total number of exposed patients). The background rate of thyroid cancer in the diabetic population must also be considered, as diabetes itself may be associated with a modestly increased cancer risk.
Observational studies examining real-world data have yielded mixed results. Some studies suggest no increased risk, whilst others have found small, non-significant trends. Recent large cohort analyses published in peer-reviewed journals between 2020-2023 have shown inconsistent findings, with some suggesting potential signals requiring further investigation. Current evidence does not support a significant association between GLP-1 receptor agonists and thyroid cancer in humans, though longer-term surveillance remains important given the typically slow progression of MTC.
Patients taking Victoza should be aware of established risk factors for medullary thyroid carcinoma and warning signs that warrant medical evaluation. A personal or family history of MTC or multiple endocrine neoplasia syndrome type 2 (MEN 2) represents a significant risk factor. The UK SmPC advises that patients with thyroid disease should be monitored and counselled about potential risks, with particular vigilance for those with relevant medical or family history.
Other risk factors for thyroid cancer more broadly include previous radiation exposure to the head and neck (particularly in childhood), certain genetic syndromes, iodine deficiency (less common in the UK), and possibly obesity and diabetes themselves. Age and gender also play roles, with thyroid cancer being more common in women and typically diagnosed between ages 25–65.
Warning signs that should prompt urgent GP consultation include:
A persistent lump or swelling in the neck, particularly if it grows over time
Hoarseness or voice changes lasting more than three weeks
Difficulty swallowing (dysphagia) or a sensation of something stuck in the throat
Persistent cough unrelated to infection or other respiratory conditions
Difficulty breathing or noisy breathing (stridor)
Unexplained neck or throat pain
It is important to emphasise that these symptoms are far more commonly caused by benign conditions than cancer. However, any persistent or progressive neck symptoms warrant clinical assessment. According to NICE guideline NG12 (Suspected cancer: recognition and referral), unexplained thyroid lumps should be considered for urgent ultrasound assessment within two weeks, with suspected cancer pathway referrals based on ultrasound risk features.
Patients should not discontinue Victoza without consulting their healthcare provider, as abrupt cessation may lead to deterioration in glycaemic control.
The Medicines and Healthcare products Regulatory Agency (MHRA) has issued specific guidance regarding the safe use of Victoza in light of the theoretical thyroid cancer risk identified in animal studies. The current UK Summary of Product Characteristics (SmPC) for Victoza includes important safety information that prescribers and patients should understand.
The UK SmPC for Victoza includes special warnings and precautions regarding thyroid disease. It notes that in clinical trials and post-marketing surveillance, thyroid adverse events, including increased blood calcitonin, goitre, and thyroid neoplasm, have been reported. The SmPC advises that patients with thyroid disease should be monitored and counselled about the potential risk. Whilst the US labelling contains a boxed warning about MTC risk, the UK and European labelling approach differs, focusing on clinical vigilance and patient counselling rather than formal contraindications for patients with MTC/MEN2 history.
Routine screening for MTC with serum calcitonin measurements is not recommended in the general population taking Victoza, as this approach has not been proven beneficial and may lead to false-positive results and unnecessary investigations.
Patients should be counselled about the potential risk and advised to report symptoms suggestive of thyroid tumours, including a neck mass, persistent hoarseness, dysphagia, or dyspnoea. The MHRA encourages both healthcare professionals and patients to report any suspected adverse reactions through the Yellow Card scheme, which can be accessed online at yellowcard.mhra.gov.uk or via the Yellow Card app.
Prescribing decisions should involve shared decision-making, weighing the proven benefits of Victoza against the theoretical thyroid cancer risk. For most patients without thyroid disease, the established benefits in reducing HbA1c and the potential cardiovascular benefits shown in the LEADER trial outweigh the uncertain thyroid cancer risk. However, individual circumstances, patient preferences, and alternative treatment options should always be considered. The MHRA continues to monitor safety data and will update guidance if new evidence emerges regarding the thyroid cancer risk in humans.
For patients concerned about the theoretical thyroid cancer risk associated with Victoza, or for those with thyroid disease, numerous alternative treatments for type 2 diabetes are available. Treatment selection should follow NICE guidance (NG28), considering individual patient factors including cardiovascular risk, renal function, weight, hypoglycaemia risk, and patient preferences.
First-line therapy options depend on individual circumstances. Metformin remains a foundation therapy for many patients with type 2 diabetes, improving insulin sensitivity with a favourable safety profile. However, NICE now recommends SGLT2 inhibitors (sodium-glucose co-transporter-2 inhibitors) such as dapagliflozin, empagliflozin, and canagliflozin as first-line options (with or without metformin) for patients with chronic kidney disease, heart failure, or established/high risk of cardiovascular disease. SGLT2 inhibitors work by increasing urinary glucose excretion and do not carry thyroid cancer warnings.
Other GLP-1 receptor agonists in the same class as Victoza include dulaglutide (Trulicity), semaglutide (Ozempic for diabetes, Rybelsus as an oral formulation), and exenatide (Byetta, Bydureon). These agents share similar special warnings regarding thyroid C-cell tumours based on animal data. Cardiovascular outcome trials have demonstrated benefits with liraglutide, semaglutide and dulaglutide, though evidence varies between agents. Some offer once-weekly dosing options which may improve adherence.
DPP-4 inhibitors (dipeptidyl peptidase-4 inhibitors) like sitagliptin, linagliptin, and saxagliptin offer another option with a low hypoglycaemia risk and weight-neutral effects, though they are generally less potent than GLP-1 agonists for glycaemic control.
Traditional options including sulfonylureas (gliclazide), thiazolidinediones (pioglitazone), and insulin therapy remain important tools, each with distinct benefit-risk profiles. Patients should discuss their individual circumstances, treatment goals, and concerns with their diabetes care team to identify the most appropriate therapeutic approach. Regular review and treatment adjustment are essential components of effective diabetes management, and switching medications when concerns arise is a normal part of personalised care.
No, there is no definitive evidence that Victoza causes thyroid cancer in humans. Whilst animal studies showed thyroid tumours in rodents, large clinical trials and post-marketing surveillance have not confirmed a causal link in people.
Routine calcitonin screening or thyroid ultrasound is not recommended for patients taking Victoza. However, you should report any persistent neck lumps, hoarseness, difficulty swallowing, or voice changes to your GP promptly.
Yes, several alternatives exist including SGLT2 inhibitors, metformin, and DPP-4 inhibitors, which do not carry thyroid cancer warnings from animal studies. Discuss options with your diabetes care team to find the most suitable treatment for your circumstances.
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