The Largest Study Yet Found GLP-1 Users Had a Lower Risk of Obesity-Related Cancers, With a Bigger Effect in Women

Obesity is one of the most established preventable causes of cancer, linked to at least 13 to 14 different cancer types. Until recently, no medication had been shown to lower the cancer risk that comes with it. That is the gap this research set out to fill, and it is why the finding drew attention when it was presented at the 2025 American Society of Clinical Oncology annual meeting.

What the study looked at

The analysis used a method called target-trial emulation, which takes large amounts of real-world patient data and structures it to imitate a randomized trial as closely as possible. Researchers compared adults who had both type 2 diabetes and obesity and who started one of two drug classes between 2013 and 2023: GLP-1 receptor agonists, the family that includes semaglutide and tirzepatide, or DPP-4 inhibitors, an older class of diabetes pills. Half the patients started each class.

Comparing the two groups matters. Because everyone in the study had diabetes and obesity, the question was not "drug versus nothing," but "does this newer class lower cancer risk more than the older one." The lead investigator was Lucas Mavromatis, and the work was presented at ASCO 2025 and published in abstract form in the Journal of Clinical Oncology.

The numbers

People who took a GLP-1 had a 7% lower risk of developing an obesity-related cancer and an 8% lower risk of dying from any cause, compared with people who took a DPP-4 inhibitor.

The effect was not spread evenly across cancer types. The reductions were largest for colorectal cancers: roughly a 16% lower risk of colon cancer and a 28% lower risk of rectal cancer. Across all 14 obesity-related cancers the team examined, rates were similar or lower in the GLP-1 group. None of the 14 showed an increase.

For this audience, the most relevant detail is the sex difference. Women on GLP-1s had about an 8% lower risk of obesity-related cancer, a result the researchers described as statistically meaningful. In men, the difference did not reach statistical significance. The researchers did not claim to know why, but a sex-specific effect is worth following, because several obesity-related cancers, including breast and endometrial cancer, are far more common in women.

The thyroid cancer question

A lot of the online worry about GLP-1s and cancer traces back to thyroid cancer specifically. That concern came from early animal studies and from warning labels on some of these drugs. It is a fair thing to have heard about, so it is worth being clear on where the evidence now stands.

More recent and much larger human studies, including a Scandinavian cohort study and other long-term analyses, have not found that GLP-1 use raises the risk of thyroid cancer. In the ASCO analysis, thyroid cancer was among the 14 cancers tracked, and like the others it did not increase in the GLP-1 group. The early signal has not held up as the data has gotten bigger.

What this study cannot say

This is the part the headlines tend to skip. The analysis was observational. It emulates a trial, but it is not one, so it cannot prove that GLP-1s cause the lower cancer rates.

"These data are reassuring, but more studies are required to prove causation," Mavromatis noted. There are also plausible explanations that sit alongside any direct anti-cancer effect. GLP-1s produce substantial weight loss, and losing weight is itself associated with lower obesity-related cancer risk, so part of what the study captured may simply be the downstream benefit of the weight change rather than a special property of the drug. The reductions were also modest. A 7% relative reduction is real and, across millions of people, potentially important at a population level, but it is not the kind of dramatic effect that should drive any individual decision.

Why it matters for this audience

Two things are worth holding onto. First, the widely shared claim that these drugs increase cancer risk is not supported by the largest evidence available; if anything, the data trends in the opposite direction for obesity-related cancers. Second, the signal was strongest in exactly the group that reads this site, women, and in the cancers, colorectal, where screening and prevention conversations are already common.

None of this is a reason to start or stop a medication. It is a reason to be skeptical of the scarier version of the GLP-1 story that circulates online, and to bring the actual evidence, limitations included, to any conversation with your own clinician.