St Louis: Growing interest in whether GLP-1 drugs such as Ozempic could reduce cancer risk has been fuelled by several recent studies. However, researchers say the evidence remains inconclusive and that more long-term trials are needed.
The early cancer concerns
Before the current buzz that GLP-1 drugs could reduce cancer risk, the worry ran in the opposite direction: that they might raise cancer risk.
Researchers were originally concerned about thyroid cancer. Studies in rodents found that Ozempic caused thyroid C-cell tumours, which is why US regulators added a black box warning to the drug in June 2026, advising against its use in people with a personal or family history of related conditions.
But rodents are not people. Human thyroid C cells are less sensitive to GLP-1 drugs than rodent C cells because they have far fewer GLP-1 receptors. Long-term studies in monkeys did not show the same abnormal thyroid cell growth seen in rodents.
A 2025 analysis of data from 93 clinical trials found no clear link between taking certain GLP-1 drugs and thyroid cancer. European regulators reached the same conclusion in 2023 after reviewing available research on GLP-1 drugs.
Pancreatic cancer was another concern. Here, too, researchers found no consistent increased risk from taking GLP-1 drugs in a 2025 analysis of data from 62 studies.
The reassurance is real but provisional. These drugs are relatively new, and cancer can take decades to surface.
The cancer story turns on its head
GLP-1 drugs, once scrutinised for possibly causing cancer, are now being discussed as drugs that might prevent or even treat cancer.
A 2024 study of more than 1.6 million people with type 2 diabetes found lower rates of 10 out of 13 obesity-related cancers in people treated with a GLP-1 drug compared with those treated with insulin.
A 2025 study of about 87,000 adults found that overall cancer rates among those who started a GLP-1 drug were roughly 17 per cent lower, with the clearest reductions in endometrial and ovarian cancers as well as a type of brain cancer called meningioma. The risk of kidney cancer was 38 per cent higher among patients taking GLP-1 drugs, though larger studies are needed to confirm its significance.
A 2026 study of more than 110,000 women undergoing breast imaging found a roughly 30 per cent lower risk of breast cancer among those who used GLP-1 drugs compared with those who did not.
Why the evidence is so easy to misread
While these findings are exciting, studies on the effects of GLP-1 drugs on cancer risk have three features that make them especially easy to misread.
The first is healthy user bias. People who start a GLP-1 drug tend to be healthier and wealthier than those who do not. A person with obesity who has insurance, sees doctors regularly and can afford Ozempic is far more likely to start the drug than someone with the same height and weight who lacks those advantages.
Healthy user bias is very difficult to eliminate from observational studies, which compare people as they are treated in real life rather than assigning the drug at random. The very advantages that made it possible to receive a GLP-1 prescription, not the drug itself, may be what lowered a patient’s cancer risk.
The second is the choice of the comparison drug. To understand the effect of a drug, it has to be measured against something else. What it’s measured against will shape the results of the study. The 2024 study reported that patients taking GLP-1 drugs saw large reductions in cancer risk compared with those taking insulin. But comparing patients on GLP-1 drugs with patients taking the diabetes drug metformin showed no clear reduction in cancer risk.
Insulin is reserved for patients with more advanced diabetes, a condition that is itself a risk factor for cancer. In these studies, patients on insulin start out with a higher risk of cancer. Measured against a group at higher risk of developing cancer, almost anything can look protective. The apparent benefit came from the comparison drug, not the GLP-1 drug.
The third is timing. Cancer can take decades to develop, yet most GLP-1 studies follow people for only a handful of years. In some studies, the apparent cancer benefits of GLP-1 drugs show almost immediately. But prevention doesn’t work that quickly. A drug that truly lowered the risk of developing cancer would show its effect gradually as fewer tumours surface over time, not within the first few months of taking the drug.
What do randomised trials show?
The cleanest way around these study biases is randomised trials, which by design make comparison groups alike from the start.
Available clinical trials tell a quieter story than the headlines. Two 2025 meta-analyses, which pooled data from multiple studies — one covering 50 trials and a second covering 48 — found little evidence that GLP-1 drugs either raise or lower cancer risk.
Despite their strengths, these analyses inherit the limitations of the trials they include. Most of the trials in these 2025 studies had a short follow-up period of a year or two and recorded too few cancer cases to settle the question.
Randomised clinical trials designed to answer whether GLP-1 drugs affect cancer risk would need to enrol tens of thousands of people and follow them for many years. Short of that, the next best evidence will come from observational studies designed to emulate randomised trials.
The bottom line
Based on the available evidence, the clearest conclusion is the reassuring one: GLP-1 drugs do not appear to raise overall cancer risk. However, more ambitious claims that GLP-1 drugs actively prevent cancer or improve survival after diagnosis remain unproven.