Popular Weight-Loss Drugs Show No Clear Reduction in Obesity-Linked Cancer Risk: Major Study

A major new study has found that widely used weight-loss and diabetes drugs such as Wegovy and Zepbound do not significantly reduce the risk of obesity-related cancers, despite producing substantial weight loss and metabolic benefits. The findings, published in the peer-reviewed journal Annals of Internal Medicine, address long-standing questions about the long-term cancer safety and potential cancer-prevention benefits of glucagon-like peptide-1 (GLP-1) receptor agonists.

The results come at a time when GLP-1 drugs are being used by millions of people worldwide, amid a global obesity crisis. According to the World Health Organization (WHO), around 2.5 billion adults were overweight in 2022, including 890 million living with obesity—a condition strongly linked to multiple forms of cancer.

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Why the Question Matters

Obesity is a well-established risk factor for at least 13 types of cancer, including breast, colorectal, liver, pancreatic, kidney, ovarian, endometrial, thyroid, and oesophageal cancers. Because GLP-1 drugs lead to meaningful and sustained weight loss, researchers and clinicians have been keen to know whether these medications might also lower cancer risk—or conversely, pose new long-term risks.

Earlier observational studies and case reports produced mixed signals, with some suggesting a reduced risk of certain cancers and others raising concerns about possible links to thyroid or pancreatic cancer. This uncertainty has been a growing concern for doctors, regulators, and patients alike.

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What the Study Examined

To address these questions more rigorously, researchers conducted a systematic analysis of 48 randomised clinical trials, involving more than 94,000 participants with type 2 diabetes, overweight, or obesity. These trials primarily evaluated the safety and effectiveness of GLP-1 receptor agonists, but also recorded cancer outcomes.

The study’s corresponding author, Dr Cho-Han Chiang, clinician investigator at Mount Auburn Hospital, Harvard Medical School, said the aim was to move beyond observational data and assess cancer risk using evidence from controlled trials.

“GLP-1 receptor agonists are now being used by millions of people globally, yet their long-term cancer safety has remained uncertain,” Dr Chiang told Medical News Today. He noted that conflicting findings from earlier studies made a comprehensive review of randomised trial data essential.

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Key Findings: No Clear Cancer Benefit—So Far

The researchers found that GLP-1 drugs likely have little to no effect on the short- to intermediate-term risk of several major obesity-related cancers, including:

• Thyroid cancer

• Pancreatic cancer

• Breast cancer

• Kidney cancer

For other cancers—such as colorectal, oesophageal, and liver cancer—the evidence was judged to be low certainty, while the data on gastric (stomach) cancer was described as very uncertain.

According to the authors, these limitations stem largely from the small number of cancer cases recorded in trials and the relatively short follow-up periods, which may not be long enough to capture cancers that develop over many years.

“Our results suggest that current GLP-1 use does not meaningfully increase cancer risk in the short to intermediate term,” Dr Chiang said. “However, they also do not rule out possible harmful or beneficial effects over longer durations.”

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Why a Protective Effect Is Still Possible

Importantly, researchers caution that the absence of evidence is not the same as evidence of absence. While no clear cancer-protective effect was demonstrated in randomised trials, a potential benefit remains biologically plausible.

Dr Chiang explained that obesity promotes cancer through chronic inflammation, insulin resistance, hormonal changes, and metabolic dysfunction—all pathways that GLP-1 drugs can improve. Several real-world observational studies have also reported lower cancer rates among GLP-1 users, though such studies can be influenced by confounding factors.

“Because cancer often develops over long periods, current trials may simply be too short to detect delayed protective effects,” he said. “Long-term surveillance and extended follow-up will be critical.”

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What This Means for Patients and Doctors

For now, experts say the findings should reassure patients that GLP-1 drugs do not appear to increase cancer risk in the near term, while also tempering expectations that these medications will automatically reduce cancer risk.

Clinicians are advised to continue prescribing GLP-1 drugs based on their proven benefits for weight loss, blood sugar control, and cardiovascular risk, rather than any unproven cancer-prevention effects.

Regulators and researchers, meanwhile, are expected to closely monitor long-term outcomes as real-world use of these drugs continues to expand.