Weight-Loss Injections and Cancer: Hope or Danger?

Obesityand smoking have become the two leading causes of preventable death today, and obesity has been identified as a major risk factor for many cancers. The rapid spread of weight-loss injections such as GLP-1 receptor agonists (GLP-1 RAs), particularly in recent years, has raised questions about their relationship with cancer. Patients and healthcare professionals alike are asking whether these drugs do more than promote weight loss and also reduce cancer risk. Alongside their potential benefits, however, possible risks such as thyroid and pancreatic cancer remain on the scientific agenda.

On May 11, 2025, Lancet eClinicalMedicinepublished a comprehensive observational analysis emphasizing the need for caution on this issue.

GLP-1 Receptor Agonists: More Than Weight Loss?

GLP-1 RAs (e.g., liraglutide, dulaglutide) were initially developed for diabetes and later used to treat obesity. These injectable drugs reduce appetite, increase satiety and cause weight loss.

Some studies suggest that, beyond weight loss, these drugs may reduce cancer risk through mechanisms such as reducing inflammation, increasing insulin sensitivity, correcting hormonal balance and improving the gut microbiota.

Summary of the Lancet eClinicalMedicine Study: BMS vs GLP-1 RAs

The study used data from Israel’s Clalit Health System. It divided 3178 patients with obesity and diabetes into two groups: those who underwent bariatric surgery (BMS) and those who used GLP-1 receptor agonist (GLP-1 RA) drugs. The groups were matched for age and body mass index (BMI) at baseline.

Participants’ mean age was 52.3 and their mean BMI was 41.5 kg/m² . Both groups were followed for an average of 7.5 years.

The results showed nearly identical rates of obesity-related cancer in the two groups: 5.76% after surgery and 5.64% with GLP-1 RAs. This difference was not statistically significant.

Weight loss was greater in the surgical group (approximately 31%), compared with an average of around 14% in the GLP-1 RA group. A notable finding, however, was that GLP-1 RAs were thought to reduce cancer risk through pathways beyond weight loss, such as reducing inflammation. This effect was calculated to provide an additional risk reduction of up to 41%, independent of weight.

This finding suggests that GLP-1 RAs may reduce cancer risk not only through weight loss, but also through mechanisms such as suppression of inflammation in the body.

Thyroid and Pancreatic Cancer Risk: A Real Threat?

Although some meta-analyses suggest that GLP-1 RAs may increase thyroid cancer risk, the data are conflicting:

• Italian meta-analysis, March 2024: An increase in thyroid cancer risk was found, but it was not significant for papillary and medullary types.

• Scandinavian cohort study, April 2024: No significant increase in thyroid cancer risk over an average follow-up of 3.9 years.

• Pancreatic cancer: Although some studies based on FDA reports have raised warnings, long-term observational data have not confirmed this risk.

“Cancer Patients: Do Not Use Without Consulting Your Doctor”

It may be unsafe for patients receiving chemotherapy or hormonal therapy to use weight-loss injections on their own. These drugs may alter how the body absorbs and processes other medicines, potentially reducing the effectiveness of some cancer treatments.

Common side effects also include nausea, vomiting, abdominal pain, constipation and weakness.

In some cases, these drugs can also reduce the effectiveness of oral contraceptives. This may lead to unintended pregnancies, posing serious health risks, particularly for women receiving cancer treatment.

Always consult your doctor first.

Use Before Surgery: The Risk of a “Quick Fix” Rather Than “Prehabilitation”

Some patients want to use GLP-1 RAs to lose weight before surgery. Experts emphasize that this must be coordinated with the oncology team. Weight loss may be beneficial, but these drugs should be part of a specialist-supervised strategy rather than a “quick fix.”

Conclusion: Promising, but Caution Is Essential

GLP-1 RAs, particularly newer-generation drugs, offer promise for treating obesity and perhaps preventing cancer. However, long-term randomized controlled trials are needed to assess both safety and clinical effects.

Starting these drugs without a doctor’s recommendation may carry serious risks, particularly for cancer patients.

Scientific Summary Box

Warnings and Recommendations

• GLP-1 RAs should be used only on the recommendation of an endocrinology or oncology specialist.

• Lifestyle changes (diet, exercise, smoking cessation) remain the fundamental strategy for obesity-related cancers.

• Patients receiving oncology treatment must communicate with their doctors about concurrent medication use.