Is one of Wegovy's side effects cancer?
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Can Wegovy cause thyroid cancer as a side effect? Join us as we separate the facts from the fiction.
The injectable weight loss drug Wegovy has received a lot of press coverage in recent years.
Some articles tout its so-called 'miracle' benefits¹. Others cast a sceptical eye at the drug and its potential side effects.² Many are, frankly, a little sensationalist.
If you've been following the news, you might have heard claims that taking Wegovy comes with a thyroid cancer risk. Scary stuff.
But is the claim true?
The short answer is this. No drug is 100% risk-free – but the claim that Wegovy definitely causes thyroid cancer in humans has the whiff of 'urban myth' about it.
Let's cut through the shock headlines and get straight to the facts.
Does Wegovy cause thyroid cancer?
Wegovy, like all approved drugs, has been thoroughly tested. These tests have included animal studies, as well as human trials.
In studies with rats, Wegovy's active ingredient (semaglutide) was found to increase the risk of a rare, non-lethal cancer called 'medullary thyroid cancer'.³ No other tumours were noted.
Case closed, right?
Not quite.
First things first, people are not rats. Animal studies can help us understand how safe and effective a drug might be, but they can't account for the huge differences between species. So, while studies found a link between semaglutide and thyroid cancer in rats, this doesn't mean the same is true for humans.
Crucially, since semaglutide was approved in the US in 2017, there hasn't been a single reported case of cancer that was thought to be related.
The risk, if it exists, is thought to be low. But in medicine, safety is everything – and you can't ignore a risk, even if the risk might be vanishingly small.
That's why Wegovy comes with a warning. The patient information leaflet notes one of the side effects as being 'possible thyroid tumours, including cancer'. And it instructs users to contact a healthcare provider if they experience swelling in the neck, trouble swallowing or shortness of
breath.
And it's why we don't allow people with a history of thyroid cancer to join the SemaPen Wegovy treatment programme.
The safety and well-being of our patients are paramount. Even though no firm links have been made between Wegovy and thyroid cancer in humans, we're not willing to subject our patients to any unnecessary risk.
Is there a link between Wegovy and pancreatic cancer?
There are two foundations to this claim.
The first is that semaglutide is known to increase the risk of pancreatitis (swelling of the pancreas). The risk is small but does exist – in clinical trials, acute pancreatitis affected 0.2% of Wegovy users.⁴ That works out to one in every 500 people.
The second basis for the claim is that at least one study found a link between GLP-1-based therapies and pancreatic cancer risk. That includes a study published in 2011, which looked at around half a million patients in the US.⁵ Semaglutide is a type of GLP-1-based therapy – however, that 2011 study looked at two different active ingredients called 'sitagliptin' and 'exenatide'.
More recent evidence paints a more positive picture. In the STEP 1 trial, published in 2021, no link was found between Wegovy and any type of cancer.⁴ And a study published in January, which looked at 543,595 patients in Israel, found no link between GLP-1 drugs and pancreatic cancer risk.⁶
Still, in medicine, the maxim 'Better safe than sorry' holds true. That's why Novo Nordisk, Wegovy's manufacturer, is currently conducting its own study on the subject.⁷ The results of that study are expected to be published in 2026.
Sources
3. https://medlineplus.gov/druginfo/meds/a618008.html
4. Wilding, J.P.H. et al. (2021) "Once-weekly semaglutide in adults with overweight or obesity" New England Journal of Medicine, 384(11) https://doi.org/10.1056/NEJMoa2032183
5. Elashoff, M. et al. (2011) "Pancreatitis, Pancreatic, and Thyroid Cancer With Glucagon-Like Peptide-1-Based Therapies" Gastroenterology, 141(1) https://doi.org/10.1053/j.gastro.2011.02.018
6. Danker, R. et al (2024) "Glucagon-Like Peptide-1 Receptor Agonists and Pancreatic Cancer Risk in Patients With Type 2 Diabetes" JAMA Network Open, 7(1) https://doi.org/10.1001/jamanetworkopen.2023.50408
7. https://catalogues.ema.europa.eu/node/3397/administrative-details
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