Metformin
Metformin, a prescription drug used to manage diabetes, has shown some benefits in lower risks of cancer and better survival, mostly among people with diabetes or high blood sugar.
Metformin at a glance
Metformin is a prescription drug used to control high blood glucose in type 2 diabetes. Some integrativein cancer care, a patient-centered approach combining the best of conventional care, self care, and evidence-informed complementary care in an integrated plan cancer care physicians use metformin off-label for cancer treatment, use 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.
Metformin is linked to lower risks of some types of cancer and also better outcomes in people with many types of cancer, although most benefits are seen among people with diabetes or other metabolic abnormalities. Very little evidence shows better cancer outcomes among people without diabetes taking metformin.
We strongly recommend that you do not take metformin unless it is prescribed for you, nor order metformin from online pharmacies (or any other source) without a prescription from a licensed physician. If you are exploring taking metformin as an off-label drug for your cancer, we advise working with a licensed physician who has experience and expertise in using it for this purpose.
CancerChoices ratings for metformin
We rate metformin on seven attributes, with 0 the lowest rating and 5 the highest. We rate the strength of the evidence supporting the use of metformin for a medical benefit, such as improving treatment outcomes or managing side effects.
See how we evaluate and rate complementary therapies ›
Improving treatment outcomes
See MoreAlmost all the benefits related to cancer outcomes are limited to people with diabetes or perhaps other metabolic abnormalities.
Diabetic people with many types of cancer treated with metformin have shown better survival across many observational studies (but not advanced cancer, acute lymphoblastic leukemia, or follicular lymphoma, and inconclusive results for cervical cancer). In many studies, people with diabetes treated with metformin show comparable survival to people without diabetes. Generally, we expect to see worse survival among people with diabetes and cancer. Diabetic people have also shown slower cancer progression, higher markers of a tumor suppressor, and less metastases when treated with metformin in some studies.
Among nondiabetic people with many types of cancer, metformin has not shown an effect on progression-free or overall survival, although some studies have found more tumor response to treatment, lower markers of proliferation, or less metastasis. Some studies have found worse survival among nondiabetic people with liver cancer, lung cancer, and possibly breast cancer treated with metformin, as described in Safety and precautions ›
Optimizing your body terrain
See MoreBody weight: Nondiabetic people with cancer treated with metformin showed more weight loss across several studies. People with prostate cancer and normal blood sugar showed lower weight gain in the short term but not the long term during androgen deprivation therapy—which often results in weight gain—in one study.
High blood sugar and insulin resistance: Nondiabetic people with blood cancer treated with metformin showed lower blood sugar, insulin, and insulin resistance across several studies.
Sex hormones: Nondiabetic people with breast cancer treated with metformin showed lower levels of many sex hormones.
Metabolic hormones: People with cancer or major depressive disorder treated with metformin showed lower levels of insulin-like growth factor 1 (IGF-1) across several studies. Nondiabetic people with cancer treated with metformin showed lower levels of leptina hormone that helps regulate energy balance by inhibiting hunger across several studies. People with polycystic ovary syndrome treated with metformin showed higher levels of adiponectina hormone and signaling protein involved in regulating glucose levels and fatty acid breakdown across several studies. Nondiabetic people with thyroid nodules and insulin resistance showed lower levels of thyroid-stimulating hormone when treated with metformin in one study.
Immune function: Nondiabetic people with head and neck cancer treated with metformin before surgery showed higher markers of immune function in one poorly designed study. In another poorly designed study, people with esophageal cancer, whether with or without diabetes, treated with metformin before surgery also showed higher markers of immune activation.
Inflammation: Nondiabetic people with breast or colorectal cancer or with polycystic ovary syndrome or major depressive disorder treated with metformin showed lower levels of markers of inflammation across several studies.
Oxidative stress: Nondiabetic people with colorectal cancer or major depressive disorder treated with metformin during chemotherapy showed lower markers of oxidative stress in a couple of studies.
Your microbiome: Nondiabetic, obese people with solid tumors treated with metformin showed changes in the gut microbiome, including beneficial increases in butyrate, a fatty acid that promotes gut health, in one study.
Managing side effects and promoting wellness
See MoreNondiabetic people with metastatic breast cancer treated with metformin during chemotherapy had less incidence of low levels of white blood cells (neutropenia) in one study.
Nondiabetic people undergoing chemotherapy for breast cancer treated with metformin showed less fatigue in one study.
Nondiabetic people undergoing chemotherapy for breast cancer treated with metformin had a lower rate of fatty liver in one study.
Nondiabetic people with breast or colorectal cancer treated with metformin showed less chemotherapy-induced neuropathy in two studies.
Nondiabetic people with breast cancer treated with metformin had less oral mucositis during chemotherapy in one study.
People with breast cancer treated with metformin showed lower endometrial thickness during tamoxifen treatment.
People with diabetes (but not specific to cancer) treated with metformin had a lower risk of bone fractures in two large studies.
Nondiabetic people with major depressive disorder treated with metformin showed lower depression scores in one study.
Reducing cancer risk
See MorePeople with type 2 diabetes are at higher risk for cancer due to specific diabetes-related processes that promote cancer. Metformin thwarts some of these cancer-promoting processes and helps correct terrain imbalances due to diabetes. As a result, we are not surprised to find that metformin shows the biggest benefits among people with cancer types linked to type 2 diabetes, insulin resistancea condition in which cells in your muscles, fat, and liver don’t respond well to insulin and can’t efficiently take up glucose from your blood for energy, and/or high blood sugar.
Recurrence: Diabetic people with many types of cancer treated with metformin have shown a lower risk of recurrence across many studies, although not ER-negative breast cancer or type 2 endometrial cancer. Among nondiabetic people, metformin has not shown any benefit for cancer recurrence across many studies.
Cancer risk: Diabetic people treated with metformin had a lower risk of many types of cancer and cancer mortality across many studies, although not breast cancer, and evidence is inconclusive regarding prostate cancer and endometrial cancer.
Use by integrative oncology experts
See More- Limited use by our program sources (fewer than four)
- Not mentioned in cancer clinical practice guidelines
Safety
See More- Extreme caution is needed with use by people with specific conditions; may interact with other treatments and may increase risk of poor outcomes among nondiabetic people with liver cancer and higher proliferation among nondiabetic people with breast cancer
- Side effects are common, especially when starting use, and usually mild. Serious side effects are rare but may require swift attention.
- Supervision by a medical professional is highly recommended.
Affordability and access
See More- Available with a prescription from a licensed physician
- Inexpensive to somewhat expensive (less than $2000 US/year), depending on the dose
- Prescriptions may be covered by insurance
Keep reading about metformin
Authors
Ms. Hepp is a researcher and communicator who has been writing and editing educational content on varied health topics for more than 20 years. She serves as lead researcher and writer for CancerChoices and also served as the first program manager. Her graduate work in research and cognitive psychology, her master’s degree in instructional design, and her certificate in web design have all guided her in writing and presenting information for a wide variety of audiences and uses. Nancy’s service as faculty development coordinator in the Department of Family Medicine at Wright State University also provided experience in medical research, plus insights into medical education and medical care from the professional’s perspective.
Sophie received her Bachelor of Arts from the University of Cambridge, where she studied Middle Eastern languages and the philosophy of science. She then completed a premedical post-baccalaureate at the City University of New York. Before joining CancerChoices, she worked for several years at the Cornell Center for Research on End-of-Life Care, where she helped to conduct research on terminal illness and grief. Working in end-of-life research filled her with the conviction that all patients deserve free, accessible, and scientifically accurate information about the therapies available to them. While taking classes in anthropology, she also became curious about traditional medical knowledge and philosophies. These interests led her to CancerChoices. She is delighted to be part of CancerChoices’s work creating rigorous, evidence-based treatment guides for patients and physicians.
Andrew Jackson, ND, serves as a CancerChoices research associate. As a naturopathic physician practicing in Kirkland, Washington, he teaches critical evaluation of the medical literture at Bastyr University in Kenmore, Washington. His great appreciation of scientific inquiry and the scientific process has led him to view research with a critical eye.
Reviewers
Laura Pole is senior clinical consultant for CancerChoices. Laura is an oncology clinical nurse specialist who has been providing integrative oncology clinical care, navigation, consultation, and education services for over 40 years. She is the co-creator and co-coordinator of the Integrative Oncology Navigation Training at Smith Center for Healing and the Arts in Washington, DC. Laura also manages the “Media Watch Cancer News That You Can Use” listserv for Smith Center/Commonweal. In her role as a palliative care educator and consultant, Laura has served as statewide Respecting Choices Faculty for the Virginia POST (Physician Orders for Scope of Treatment) Collaborative as well as provided statewide professional education on palliative and end-of-life care for the Virginia Association for Hospices and Palliative Care.
For CancerChoices, Laura curates content and research, networks with clinical and organizational partners, brings awareness and education of integrative oncology at professional and patient conferences and programs, and translates research into information relevant to the patient experience as well as clinical practice.
Laura sees her work with CancerChoices as a perfect alignment of all her passions, knowledge and skills in integrative oncology care. She is honored to serve you.
Dr. Fuller-Shavel is a GMC-registered integrative medicine doctor with degrees in medicine and natural sciences from the University of Cambridge. Dr. Fuller-Shavel is a fellow of the College of Medicine and the vice chair for BSIO (British Society for Integrative Oncology). Alongside her science and medical training, Dr. Fuller-Shavel holds multiple qualifications in nutrition, integrative medicine, health coaching, herbal medicine, yoga, mindfulness and other mind-body approaches.
Dr. Fuller-Shavel is the director of Synthesis Clinic, an award-winning multidisciplinary integrative medicine practice in Hampshire, UK, specializing in women’s health, gut health (microbiome and gut-brain axis) and mental health. She combines her clinical work in women’s health and supporting patients with breast and gynecological cancer with education and training for healthcare professionals and research in precision cancer medicine and precision nutrition.
Last update: January 28, 2025
Last full literature review: March 2022
CancerChoices provides information about integrativein cancer care, a patient-centered approach combining the best of conventional care, self care, and evidence-informed complementary care in an integrated plan cancer care. We review complementaryin cancer care, complementary care involves the use of therapies intended to enhance or add to standard conventional treatments; examples include supplements, mind-body approaches such as yoga or psychosocialtherapy, and acupuncture therapies and self carelifestyle actions and behaviors that may impact cancer outcomes; examples include eating health-promoting foods, limiting alcohol, increasing physical activity, and managing stress practices to help patients and professionals explore and integrate the best combination of conventionalthe cancer care offered by conventionally trained physicians and most hospitals; examples are chemotherapy, surgery, and radiotherapy and complementary therapies and practices for each person.
Our staff have no financial conflicts of interest to declare. We receive no funds from any manufacturers or retailers gaining financial profit by promoting or discouraging therapies mentioned on this site.