Do diabetes medicines affect cancer risk? For most classes, the evidence is too limited or mixed to give a firm answer. The American Diabetes Association (ADA) says metformin and sulfonylureas may have anticancer properties, that data for pioglitazone are mixed with a previous concern about bladder cancer, and that GLP-1 receptor agonists have so far not been shown to be associated with the incidence of thyroid cancer, pancreatic cancer, or any other cancer in humans. A 2010 consensus report said cancer risk should not be a major factor in choosing among diabetes therapies for the average patient. Do not stop or start a medicine because of cancer headlines without asking your prescriber.
Key takeaways
- The ADA says recommendations about diabetes medicines and cancer cannot be made at this time, because the evidence is not strong enough.
- Some medicine labels carry specific cancer-related warnings. GLP-1 medicines such as semaglutide and tirzepatide carry a boxed warning about thyroid tumors seen in rodents, and pioglitazone's label says it may increase the risk of bladder cancer.
- A large randomized trial of insulin glargine found no difference in cancer rates compared with standard care.
- Studies of diabetes medicines are hard to interpret because people on different medicines differ in many other ways.
- Stopping a medicine on your own can leave blood sugar uncontrolled. Ask your prescriber first.
Diabetes Medicines and Cancer: The Short Answer
- No medicine class has been shown to be a clear cause of cancer in people with diabetes. The evidence for most is observational or mixed.
- Two classes carry specific label warnings. One is GLP-1 and tirzepatide medicines (the Ozempic and Mounjaro labels describe thyroid tumors in rodents). The other is pioglitazone (bladder cancer).
- Metformin and sulfonylureas may have anticancer properties, according to the ADA. That is not the same as proof that they prevent cancer.
- Diabetes itself raises the risk of some cancers. Our guide on whether diabetes increases cancer risk covers that link.
- Changes to a medicine plan belong with your prescriber. Cancer news is a reason to ask a question, not to change a dose.
Why This Is Hard to Study
Most of what is known comes from observational studies, which compare people who happened to take different medicines. Those groups can differ in age, weight, how long they have had diabetes, and how well their blood sugar is controlled, and diabetes itself is linked to some cancers. The 2010 ADA and American Cancer Society (ACS) consensus report said the early evidence on insulin was confounded by other factors, and that the small number of studies on sulfonylureas had low power and made it hard to tell whether the medicine raised risk or the comparison medicine lowered it. The report's recommendations are the authors' opinions and not an official position of either organization.
Randomized trials answer the question more cleanly, but few were designed to count cancers over many years. That is why the sections below separate what trials found from what observational studies suggest.
What the Sources Say About Each Class
| Class | What the sources say | Questions it raises |
|---|---|---|
| Metformin | The ADA says metformin may have anticancer properties. The 2010 consensus report said early evidence suggested lower cancer risk | Not proof that it prevents cancer (see trials below) |
| Sulfonylureas | The ADA says sulfonylureas may have anticancer properties. The 2010 report said a small number of observational studies found higher cancer risk than with metformin, with low power | The two sources point in different directions, and neither is a randomized trial |
| Pioglitazone | The ADA says data are mixed, with a previous concern for bladder cancer, and that recommendations cannot be made at this time. The label says it may increase the risk of bladder cancer | Ask about any history of bladder cancer |
| GLP-1 medicines and tirzepatide | The ADA says GLP-1 receptor agonists have not been shown to be associated with thyroid, pancreatic, or any other cancer in humans so far. The Ozempic and Mounjaro labels carry a boxed warning about thyroid C-cell tumors in rodents | Ask about personal or family history of medullary thyroid cancer |
| Insulin | The 2010 report said early evidence suggested higher risk, confounded by other factors. A large randomized trial found no difference | See the trial below |
Other classes, including SGLT2 inhibitors and DPP-4 inhibitors, are not covered by the sources cited here. Ask your prescriber about any medicine you take.
Metformin: Trials and What They Do Not Show
Metformin gets the most attention because observational studies suggested lower cancer rates in people who take it. Randomized trials have tested it differently. In the MA.32 trial, published in JAMA in 2022, 3,649 people with early breast cancer, none of whom had diabetes, took metformin or placebo for 5 years. Metformin did not improve invasive disease-free survival (hazard ratio 1.01, 95% confidence interval 0.84 to 1.21). A follow-up analysis in the Journal of Clinical Oncology in 2023 counted new primary cancers: 102 in the metformin group and 82 in the placebo group (hazard ratio 1.25, 95% confidence interval 0.94 to 1.68, P=.13). The difference was not statistically significant, and the trial did not show a reduction in people without diabetes.
These trials tested metformin as an add-on to breast cancer care in people without diabetes. They do not show what happens in people who take metformin to manage diabetes. Our guide on how metformin works explains what the medicine does, and our guide on whether metformin causes vitamin B12 deficiency covers a better-established side effect.
Insulin: What a Large Trial Found
The ORIGIN trial randomized 12,537 people with dysglycemia, which includes prediabetes and early diabetes, who were at high risk for cardiovascular events, to insulin glargine or standard care. Over a median of 6.2 years, 953 people developed cancer. The cancer rate was 1.32 per 100 person-years in both groups (P=0.97). Cancer deaths and specific cancer types did not differ. The authors also reported that glucose-lowering therapies, including metformin, and HbA1c level during the study did not alter cancer risk.
The 2010 consensus report noted a separate five-year trial of glargine versus NPH insulin that found no excess of cancers. These results are reassuring for glargine in these groups, but they do not cover every insulin, every dose, or every person. Many people with type 1 diabetes and some with type 2 need insulin to stay safe. Our guide on whether people with type 2 diabetes need insulin explains when.
Pioglitazone and Bladder Cancer
The prescribing information for pioglitazone (Actos) says it may increase the risk of bladder cancer and should not be used in people with active bladder cancer. It says the benefits of glycemic control should be weighed against unknown risks of cancer recurrence in people with a prior history of bladder cancer. The label summarizes the studies behind the warning:
| Study (per the label) | Result |
|---|---|
| PROactive trial, about 3 years | Bladder cancer in 14 of 2,605 people (0.54%) on pioglitazone and 5 of 2,633 (0.19%) on placebo |
| 13 years of that trial plus follow-up | Hazard ratio 1.00 (95% confidence interval 0.59 to 1.72) |
| U.S. cohort, 10 years | Hazard ratio 1.06 (95% confidence interval 0.89 to 1.26) |
| UK cohort | Hazard ratio 1.63 (95% confidence interval 1.22 to 2.19) |
The label itself says these inconsistent findings preclude conclusive interpretations. The ADA's wording matches the mixed picture: data are mixed, and it makes no recommendation at this time. If you take pioglitazone, ask your prescriber whether your history makes this warning relevant to you and which symptoms to report.
GLP-1 Medicines, Tirzepatide, and Thyroid Tumors
The U.S. Food and Drug Administration (FDA) prescribing information for Ozempic (semaglutide) carries a boxed warning. It says semaglutide caused thyroid C-cell tumors in rodents and that it is unknown whether it causes these tumors, including medullary thyroid carcinoma, in humans. The medicine is not for people with a personal or family history of medullary thyroid carcinoma or with multiple endocrine neoplasia syndrome type 2. The label tells prescribers to counsel patients about symptoms of thyroid tumors, such as a neck mass, trouble swallowing, shortness of breath, and persistent hoarseness. The Mounjaro (tirzepatide) label carries the same boxed warning, based on rat studies.
The ADA says GLP-1 receptor agonist use has not been shown to be associated with thyroid cancer, pancreatic cancer, or any other cancer in humans so far. Both can be true at once: the warning reflects animal findings and unanswered human questions, and the ADA reflects human data to date. Tell your prescriber about any family history of medullary thyroid cancer before you start. Our guides on whether Wegovy is for diabetes and on tirzepatide, gallbladder, and pancreatitis warning signs cover other label warnings, and our guide on diabetes and pancreatic cancer covers that cancer.
What to Do With This Information
The 2010 consensus report said cancer risk should not be a major factor in choosing among diabetes therapies for the average patient, and that for patients at very high risk of a particular cancer, the question deserves more careful consideration. Controlling blood sugar protects the eyes, kidneys, nerves, and heart, and stopping a medicine on your own can undo that. Our guide on starting type 2 diabetes medication covers how those choices are usually made.
If you have both diabetes and cancer, ACS says your diabetes doctor and your cancer care team should work together. Steroids given with cancer treatment can raise blood sugar, which our guide on whether prednisone raises blood sugar explains. The habits that lower cancer risk, from healthy weight to recommended screening, are covered in our guide on which cancer screenings people with diabetes need.
Questions to Ask Your Care Team
- Do any of my diabetes medicines carry cancer-related warnings?
- Does my family history of thyroid, bladder, or other cancers change which medicine is a good fit?
- If I have had cancer, does that change my medicine plan?
- Who adjusts my diabetes medicines if I start cancer treatment?
- Which symptoms should I report right away?
Frequently Asked Questions
Do diabetes medicines cause cancer?
No medicine class has been shown to be a clear cause of cancer in people with diabetes. The ADA says metformin and sulfonylureas may have anticancer properties, data for pioglitazone are mixed, and GLP-1 receptor agonists have not been shown to be associated with cancer in humans so far. Ask your prescriber about your own situation.
Does metformin lower cancer risk?
Observational studies suggested it might, and the ADA says metformin may have anticancer properties. A randomized trial of metformin in 3,649 people with breast cancer who did not have diabetes found no improvement in disease-free survival. It did not test metformin for people who take it to manage diabetes.
Does insulin cause cancer?
Early observational studies suggested higher risk, but they were confounded by other factors. In the ORIGIN randomized trial of 12,537 people, cancer rates were 1.32 per 100 person-years with insulin glargine and with standard care. Many people need insulin, so do not stop it without asking your prescriber.
Do GLP-1 medicines such as Ozempic cause thyroid cancer?
The Ozempic label carries a boxed warning because semaglutide caused thyroid C-cell tumors in rodents, and it says it is unknown whether it does so in humans. The ADA says GLP-1 receptor agonists have not been shown to be associated with thyroid cancer in humans so far. The medicine is not for people with a personal or family history of medullary thyroid carcinoma.
Does pioglitazone cause bladder cancer?
The label says pioglitazone may increase the risk of bladder cancer, but it also says the studies are inconsistent and preclude conclusive interpretations. The ADA says data are mixed and makes no recommendation. Talk with your prescriber, especially if you have had bladder cancer.
Should I stop my medicine because of cancer risk?
Not on your own. The 2010 consensus report said cancer risk should not be a major factor in choosing among diabetes therapies for the average patient, while more careful consideration may be needed for people at very high risk of a particular cancer. Ask your prescriber before changing anything.
References
- American Diabetes Association Professional Practice Committee for Diabetes. "4. Comprehensive Medical Evaluation and Assessment of Comorbidities: Standards of Care in Diabetes—2026." Diabetes Care. 2026;49(Suppl. 1):S61–S88. Accessed October 2026.
- Giovannucci E, Harlan DM, Archer MC, et al. "Diabetes and cancer: a consensus report." Diabetes Care. 2010;33(7):1674–1685. Accessed October 2026.
- U.S. Food and Drug Administration. "OZEMPIC (semaglutide) injection: prescribing information." Revised May 2026. Accessed October 2026.
- U.S. Food and Drug Administration. "MOUNJARO (tirzepatide) injection: prescribing information." Revised August 2026. Accessed October 2026.
- Takeda Pharmaceuticals. "ACTOS (pioglitazone) tablets: prescribing information." Revised March 2025. Accessed October 2026.
- Goodwin PJ, Chen BE, Gelmon KA, et al. "Effect of Metformin vs Placebo on Invasive Disease-Free Survival in Patients With Breast Cancer: The MA.32 Randomized Clinical Trial." JAMA. 2022;327(20):1963–1973. Accessed October 2026.
- Goodwin PJ, Chen BE, Gelmon KA, et al. "Effect of Metformin Versus Placebo on New Primary Cancers in Canadian Cancer Trials Group MA.32: A Secondary Analysis of a Phase III Randomized Double-Blind Trial in Early Breast Cancer." Journal of Clinical Oncology. 2023;41(35):5356–5362. Accessed October 2026.
- Bordeleau L, Yakubovich N, Dagenais GR, et al. "The association of basal insulin glargine and/or n-3 fatty acids with incident cancers in patients with dysglycemia." Diabetes Care. 2014;37(5):1360–1366. Accessed October 2026.
- American Cancer Society. "Type 2 Diabetes and Cancer." Accessed October 2026.
Next Steps
Make a list of every diabetes medicine you take, including the class and the date you started it, and bring it to your next visit along with any family history of thyroid or bladder cancer. Ask the questions above before you consider any change.
For adults with type 2 diabetes or prediabetes who want lifestyle education alongside clinical care, the Done With Diabetes™ program, a holistic approach to type 2 diabetes, organizes learning about meals, movement, sleep, and stress. It does not diagnose or treat cancer or diabetes, recommend or change medicines, interpret test results, or replace your prescriber or care team.