Laura Pole, RN, MSN, OCNS, BCCT Senior Researcher
Nancy Hepp, MS, BCCT Project Manager
Last updated December 22, 2020.
Also known by these names
Evidence shows that metformin may reduce risks of some types of cancer and also may improve outcomes in people with certain cancers, especially with people with diabetes.
Metformin is a prescription drug used to control high blood glucose in type 2 diabetes. Evidence shows that metformin may reduce risks of some types of cancer and also may improve outcomes in people with certain cancers, especially with people with diabetes. Some integrative cancer care physicians use metformin off-label for cancer treatment. Off-label use is a drug’s application for a disease or condition that has not yet received FDA approval. Every US state allows drugs to be used off-label as long as enough evidence supports its use.
“Results of numerous clinical studies, although inconclusive, indicate that metformin use, and possibly cumulative duration of therapy and cumulative dose, is associated not only with decreased incidence of cancer in the diabetic population, but also with the better outcome in cancer patients. . .Definite data on the efficacy of metformin as neoadjuvant therapy in cancer patients is lacking.”1
Treating the Cancer
Donald Abrams, MD, explains how metformin can be used as a cancer therapy in a 2014 presentation.
BCCT advisor Brian Bouch, MD, explores metformin for cancer care in this interview from 2018.
Working against cancer growth or spread, improving survival, or working with other treatments or therapies to improve their anticancer action
Clinical trials using metformin as a cancer adjuvant (supplement) to cancer treatment are in progress and are described below. Most of the evidence in humans to date is from observational, population cohort and case-control studies. Evidence from these types of studies is not strong enough to conclude that metformin is the cause of the positive effects seen.
How It Works: Diabetes and Cancer
Evidence shows these intriguing relationships between diabetes and cancer:
Cancers in General
Brain and Nervous System Cancers
Lab and Animal Evidence
Managing Side Effects and Promoting Wellness
Managing or relieving side effects or symptoms, reducing treatment toxicity, supporting quality of life or promoting general well-being
- Reduced grade 3/4 neutropenia among people with metastatic breast cancer77
- Lower rate of grade 2 and 3 neuropathy, lower pain scores and lower markers of oxidative stress and heightened sensitivity to pain (hyperalgesia) among patients with colorectal cancer78
- Reduced nausea in people with lung cancer without diabetes79
Reducing the risk of developing cancer or the risk of recurrence
Clinical trials using metformin as a cancer preventive are in progress.
Cancer in General
Uterine Cancers (Endometrial and Sarcoma)
Lab and Animal Evidence
Optimizing Your Terrain
Creating an environment within your body that does not support cancer development, growth or spread
- Reduced blood glucose (glycemia);105 elevated levels are a risk factor for colorectal cancer106 and are associated with poorer survival in some reports107
- Reduced levels of insulin, fasting glucose, CRP, HOMA, leptin, BMI, and Ki-67 in breast cancer patients receiving metformin as treatment for diabetes108
- Increased phosphorylation of AMPKα109
- Physical activity and metformin both led to weight loss as well as significant changes in insulin and other biomarkers in colorectal cancer and breast cancer survivors.110
- Decrease in insulin resistance and metabolic syndrome related to androgen deprivation therapy in men without diabetes who received metformin and made lifestyle changes.111
- Did not affect expression of markers of the PI3K–Akt–mTOR or insulin signaling pathways, and did not result in weight loss among women with atypical hyperplasia or endometrioid endometrial cancer112
Metformin is available with a prescription in oral form at pharmacies.
- High-dose metformin (500-2000 mg/day) was associated with higher risk of developing lactic acidosis (buildup of lactic acid in the bloodstream) and adverse gastrointestinal effects such as diarrhea.113
- Gastrointestinal toxicity noted for prostate cancer patients receiving abiraterone therapy in a small study114
- A 2012 study by Mazzone et al. found that diabetics who developed lung cancer while receiving metformin were more likely to present with metastatic disease, had reduced survival, and had a different histology distribution (microscopic tissue characteristics) than those who were not receiving metformin.115 However, Yin et al. provided context that “the study by Mazzone et al. is the only study showing a significantly increased risk for death associated with metformin treatment whereas most of the studies in our data pool . . . favor a protective effect of metformin.”116
Common Side Effects/Adverse Events
Numerous precautions are involved in taking metformin, and patients must notify their doctors of certain conditions that will increase their risk of developing serious problems from taking metformin. For a listing of these precautions, see: WebMD: Metformin HCL: Precautions.
Metformin is not recommended in patients with abnormal renal or hepatic function, nor should it be prescribed in patients with heart failure.119
Numerous potential drug interactions are associated with metformin. Consult with your pharmacist for interactions, and discuss using metformin with your doctor. For a listing of these interactions see WebMD: Metformin HCL: Interactions.
BCCT does not recommend therapies or doses, but only provides information for patients and providers to consider as part of a complete treatment plan. Patients should discuss therapies with their physicians, as contraindications, interactions and side effects must be evaluated.
“Most of the cancer clinical trials of metformin use the same doses typically used to treat diabetes.” These are typically trials of cancer prevention. Some suggest higher doses may be more effective in the adjuvant cancer treatment setting, but safety and effectiveness of higher doses has not yet been established in clinical trials.120
Dosage information and recommendations are available from these sources:
- Lawenda, BD. Metformin Supplementation and Cancer Treatment. Integrative Oncology Essentials.
- National Cancer Institute: Metformin: Can a Diabetes Drug Help Prevent Cancer?
- See also the protocols below.
Integrative Programs, Protocols and Medical Systems
|For more information about programs and protocols, see our Integrative Programs and Protocols page.|
- Programs and protocols
We found that metformin was associated with benefit regardless of cancer treatments.
From a 2013 article by Margel et al: “There are several clinical implications of our findings. First, consistent with current guidelines, metformin should be considered first-line therapy among patients with prostate cancer and diabetes, not only for diabetes control but possibly to improve cancer prognosis. Second, we found that metformin was associated with benefit regardless of cancer treatments. These results suggest that metformin may further improve survival as an adjunct therapy, even among those already receiving optimal cancer treatments. Finally, metformin may be ideal for secondary prevention because it is inexpensive, safe, and well tolerated.124
Our results suggest that metformin is the drug of choice in the treatment of patients with cancer and concurrent type 2 diabetes.
From a 2013 article by Yin et al.: “Patients with type 2 diabetes have increased cancer risk and cancer-related mortality, which can be reduced by metformin treatment. However, it is unclear whether metformin can also modulate clinical outcomes in patients with cancer and concurrent type 2 diabetes. Our meta-analysis provided evidence that there was a relative survival benefit associated with metformin treatment compared with treatment with other glucose-lowering medications. Our results suggest that metformin is the drug of choice in the treatment of patients with cancer and concurrent type 2 diabetes..125
From a 2014 article by Yu et al: Any conclusions without a large-scale prospective randomized study should be cautious. However, “considering the high prevalence of prostate cancer in Western countries and its rising incidence in the world, [and} the low cost and favorable toxicity of metformin, the applicability of metformin use as recommendation for prevention or treatment of prostate cancer may suit multiple populations, in people both with or without type 2 diabetes, and in both developed or developing countries.”126
From a 2013 presentation by integrative oncologist and BCCT advisor Dwight McKee, MD: “Metformin can be safely given as an off-label adjunctive treatment in cancer patients, especially breast, ovarian, colorectal, prostate, pancreas and perhaps in glioma patients who have type 2 diabetes, metabolic syndrome, elevated circulating insulin levels, or are obese, or even simply those who cannot or do not adhere to a low-carb, low-fat diet.”127
From a 2009 book by integrative oncologist and BCCT advisor Keith Block, MD: If you are taking glycemic support supplements or terrain modifiers and they are not correcting your glycemic imbalance, Keith Block, MD, suggests talking with your physician about increasing the doses of these, and/or considering using metformin. “Metformin . . . is approved for insulin resistance, reduces the liver’s ability to release glucose and so may be helpful for patients whose glucose imbalance results from this mechanism.”128
Non-cancer Uses of Metformin
BCCT has not reviewed the effectiveness of this therapy for non-cancer uses. Besides diabetes, metformin has been investigated with these conditions:
BCCT has not reviewed the effectiveness of this therapy for non-cancer uses.
- Patterson S. Metformin May Have Broad Utility In Cancer. MD Anderson Cancer Center.
- Lawenda BD. Metformin Supplementation and Cancer Treatment. Integrative Oncology Essentials.
- National Cancer Institute: Metformin: Can a Diabetes Drug Help Prevent Cancer?
- Information on lifestyle practices and supplements that help manage high blood glucose and insulin as well as insulin resistance:
- Block K. Life over Cancer: The Block Center Program for Integrative Cancer Care. New York: Bantam Dell. 2009. pp. 391-407
- Alschuler LN, Gazella KA. The Definitive Guide to Cancer, 3rd Edition: An Integrative Approach to Prevention, Treatment, and Healing. Berkeley, California: Celestial Arts. 2010. pp. 224-229.
- For more information on clinical trials using metformin in either cancer prevention or treatment, see clinicaltrials.gov.
- See Table 1 in Kasznicki J, Sliwinska A, Drzewoski J. Metformin in cancer prevention and therapy. Annals of Translational Medicine. 2014;2(6):57.
- Peixoto RD, Gomes LM et al. Efficacy of oral metformin in a patient with metastatic adrenocortical carcinoma: examination of mechanisms and therapeutic implications. Rare Tumors. 2018;10:1-7.
More from Our Resources Database
- LifeExtension Nutritional Support: Cancer Adjuvant Therapy: Repurposing Common Drugs as Adjuvant Cancer Therapies
- Block KI, Block PB, Gyllenhaal C: Integrative Treatment for Colorectal Cancer
- Keith Block and others: A Broad-Spectrum Integrative Design for Cancer Prevention and Therapy
- Dwight McKee, MD, editor: Clinical Pearls
- Raymond Chang, MD: Beyond the Magic Bullet: The Anti-Cancer Cocktail