GLP-1 receptor agonists such as Mounjaro (tirzepatide) and Wegovy (semaglutide) have transformed the treatment of type 2 diabetes and obesity. As their use has increased, so too have questions about long-term safety, including whether these medications raise the risk of cancer.
At Phlo, we understand that safety concerns can feel worrying. Here’s what current research and regulatory guidance say about GLP-1 medications and cancer risk.
Is cancer considered a side effect of Mounjaro or Wegovy?
At present, cancer is not considered a common or established side effect of GLP-1 receptor agonists. However, there have been historical concerns, particularly relating to thyroid and pancreatic cancers.
So far, large human studies have not confirmed a clear increased overall cancer risk, but specific warnings remain in place as a precaution.
What does the prescribing information say about cancer risks?
All GLP-1 receptor agonists carry important safety information such as medullary thyroid carcinoma (MTC) - a rare type of thyroid cancer that arises from C-cells in the thyroid gland - where the prescribing information specifically highlights the potential risk of medullary thyroid carcinoma (MTC)
Patients are advised not to use GLP-1 medications if they have a personal history or family history of MTC or if they have Multiple Endocrine Neoplasia syndrome type 2 (MEN 2). These precautions are based on theoretical risk and animal data rather than confirmed human evidence, but they are taken seriously as a safety measure.
What evidence of risk is there between Mounjaro and thyroid cancer?
Thyroid cancer is not a single condition. The main types include:
- Papillary thyroid cancer (most common)
- Follicular thyroid cancer
- Medullary thyroid carcinoma (MTC)
- Anaplastic thyroid cancer (rare and aggressive)
The concern with GLP-1 medications relates specifically to MTC, not the more common papillary type.
Is there a risk of pancreatic cancer with Mounjaro and other GLP-1 medications?
Earlier GLP-1 drugs were associated with reports of pancreatitis, which led to speculation about a possible link to pancreatic cancer. Large observational studies and pooled clinical trial data have not demonstrated a clear increase in pancreatic cancer risk with GLP-1 receptor agonists. Regulators continue to review real-world safety data but no causal relationship has been confirmed.
Is there a risk of colorectal cancer?
Current evidence does not show an increased risk of colorectal cancer with GLP-1 receptor agonists. In fact, some emerging data suggest possible protective effects in obesity-related cancers such as colorectal cancers.
Are there concerns about other cancer types?
At present, there is no strong evidence that GLP-1 receptor agonists increase the risk of other cancers such as; breast cancer, prostate cancer or lung cancer. As with any relatively new class of medication used widely, long-term safety monitoring continues.
Can GLP-1 medications reduce cancer risk?
Interestingly, emerging research suggests the relationship between GLP-1 medications and cancer may be more complex than initially thought. A recent publication in The Lancet Regional Health Europe explored the potential association between GLP-1 receptor agonists and reduced risk of certain obesity-related cancers. Researchers are exploring several biological pathways that may explain a possible protective effect of GLP-1 receptor agonists.
These include:
- Meaningful and sustained weight reduction
- Better regulation of blood glucose and improved insulin sensitivity
- Decreased chronic, low-grade inflammation associated with obesity
- Reduced circulating insulin and insulin-like growth factor-1 (IGF-1), both of which can promote cell growth
Excess body weight is a recognised risk factor for multiple cancers, including colorectal, pancreatic, post-menopausal breast, and liver cancer. By helping to improve overall metabolic health, GLP-1 medications may indirectly influence cancer risk.
Some observational studies have reported lower rates of certain obesity-related cancers among people treated with GLP-1 receptor agonists compared with those receiving other diabetes therapies. However, this is an emerging field of research, and longer-term studies are needed to better understand the relationship.
Cancer is not considered a common side effect
Cancer is not considered a common side effect of Mounjaro or Wegovy. While there is a theoretical risk of medullary thyroid carcinoma based on findings from animal studies, this has not been clearly demonstrated in humans. Current evidence does not show an increased risk of pancreatic or colorectal cancer with GLP-1 medications. In fact, emerging research suggests there may even be potential protective effects against certain obesity-related cancers, although this area is still being studied. Regulatory authorities continue to monitor long-term safety data closely.
If you have a personal or family history of thyroid cancer, it’s particularly important to speak with a healthcare professional before starting treatment.
Speak to our team if you have questions regarding taking GLP-1 medications and risks of cancer
If you have any concerns about GLP-1 medications and potential cancer risks, the Phlo team are here to support you. Our clinicians can review your medical history, talk through any personal or family risk factors, and help determine whether treatment is safe and appropriate for you. Your health and your peace of mind are our priority, and we’re here to guide you every step of the way.
References
- U.S. Food and Drug Administration. Tirzepatide prescribing information (Mounjaro) — boxed warning about thyroid C-cell tumors and safety information. FDA medication label. https://www.accessdata.fda.gov/
- U.S. Food and Drug Administration. Semaglutide prescribing information (Wegovy and Ozempic) — warnings and precautions section. FDA medication label. https://www.accessdata.fda.gov/
- Bjerre Knudsen LB, et al. Targeting the GLP-1 receptor in rodents and humans: Differences in gene expression and pharmacology. Journal of Endocrinology and Metabolism.
- Nauck MA, Meier JJ. GLP-1 receptor agonists in obesity and metabolic disease: Mechanisms and clinical implications. Nature Reviews Endocrinology.
- Singh S, et al. GLP-1 receptor agonists and pancreatic safety: Systematic review and meta-analysis.
Gastroenterology. - American Thyroid Association. Medullary Thyroid Carcinoma and MEN2. https://www.thyroid.org/
- The Lancet Regional Health – Europe. Association of GLP-1 receptor agonist use with cancer outcomes: Emerging data (PIIS2666-7762(25)00138-3).The Lancet Regional Health – Europe. https://www.thelancet.com/journals/lanepe/article/PIIS2666-7762(25)00138-3/fulltext
- Wilding JPH, et al. Effects of semaglutide on obesity-related health outcomes (including cancer risk markers). New England Journal of Medicine.
- Davies MJ, et al. Safety and efficacy of long-term GLP-1 receptor agonists in clinical practice.
Diabetes Care. - European Medicines Agency. Safety review reports on GLP-1 receptor agonists: post-marketing surveillance and pharmacovigilance updates. https://www.ema.europa.eu/
