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.
Modest evidence of benefit
- Modest evidencesignificant effects in at least three small but well-designed randomized controlled trials (RCTs), or one or more well-designed, mid-sized clinical studies of reasonably good quality (RCTs or observational studies), or several small studies aggregated into a meta-analysis (this is the CancerChoices definition; other researchers and studies may define this differently) of lower cancer-specific mortality among people with diabetes treated with metformin
- Modest evidence of lower cancer-specific mortality among people with both bladder cancer and diabetes treated with metformin
- Modest evidence of better progression-free survival among people with both bladder cancer and diabetes treated with metformin
- Modest evidence of better overall survival among people with glioma or glioblastoma and diabetes treated with metformin
- Modest evidence of better survival among people with breast cancer and diabetes treated with metformin
- Modest evidence of a lower marker of tumor proliferation among nondiabetic women with invasive breast cancer treated with metformin before surgery
- Modest evidence of lower markers of tumor proliferation among nondiabetic people with breast cancer and higher insulin resistance treated with metformin
- Modest evidence of a lower marker of proliferation among nondiabetic people with HER2-positive DCIS lesions, and especially ER-positive/HER2-positive DCIS, treated with metformin
- Modest evidence of higher objective response rate among nondiabetic people with breast cancer treated with metformin
- Modest evidence of lower mortality, including cancer-specific mortality, among people with colorectal cancer and diabetes treated with metformin
- Modest evidence of moderately lower cancer-specific mortality among people with diabetes and colorectal cancer, including metastatic cancer, treated with metformin
- Modest evidence of better survival among people with liver cancer and diabetes treated with metformin
- Modest evidence of lower mortality among people with endometrial cancer and diabetes treated with metformin
- Modest evidence of lower risk of relapse among reproductive-aged women with atypical endometrial hyperplasia or early endometrial cancer (not specific to diabetes) treated with metformin
- Modest evidence of better survival among people with head and neck cancer and diabetes treated with metformin
- Modest evidence of lower risk of progression among people with kidney cancer and diabetes treated with metformin
- Modest evidence of lower mortality among people with type 2 diabetes and lung cancer treated with metformin
- Modest evidence of higher melanoma-specific survival among people with melanoma and diabetes treated with metformin
- Modest evidence of higher melanoma-specific survival among people with melanoma (not specific to diabetes) treated with metformin
- Modest evidence of lower mortality and higher progression-free survival among people with ovarian cancer with diabetes treated with metformin
- Modest evidence of lower mortality among people with pancreatic cancer and diabetes treated with metformin
- Modest evidence of lower mortality among people with pancreatic cancer (not specific to diabetes) treated with metformin
- Modest evidence of lower mortality among people with prostate cancer and diabetes treated with metformin
Preliminary evidence of benefit
- Preliminary evidencesignificant effects in small or poorly designed clinical studies OR conflicting results in adequate studies but a preponderance of evidence of an effect (this is the CancerChoices definition; other researchers and studies may define this differently) of longer progression-free intervals among people with glioblastoma and diabetes receiving radiation therapy and also treated with metformin
- Preliminary evidence of better progression-free survival among people with glioblastoma (not specific to diabetes) treated with metformin compared to no metformin at baseline, but no evidence of an effect with metformin during radiotherapy
- Preliminary evidence of better relapse-free survival after exemestane treatment among women with diabetes and breast tumors with high insulin-like growth factor type 1 receptor (IGF‐1R) expression treated with metformin
- Preliminary evidence of better response rates among people with breast cancer and diabetes treated with metformin
- Preliminary evidence of lower risk of relapse after exemestane treatment among people with postmenopausal hormone receptor positive breast cancer (likely with diabetes) treated with metformin
- Preliminary evidence of fewer cases of metastasis after chemotherapy and hormone therapy among nondiabetic women with breast cancer treated with metformin
- Preliminary evidence of substantially lower risk of metastasis and greater reductions in a tumor marker among people with colorectal cancer and diabetes treated with metformin
- Preliminary evidence of tumor suppression among nondiabetic people with gastrointestinal cancer (including colorectal, pancreatic, gastroesophageal, and bile duct cancers) treated with chemotherapy and metformin
- Preliminary evidence of lower risk of mortality among people with kidney cancer and diabetes treated with metformin
- Preliminary evidence of lower risk of relapse among people with acute lymphoblastic leukemia (without diabetes or mixed diabetic and nondiabetic people) treated with metformin in addition to chemotherapy
- Preliminary evidence of lower risk of progression and mortality among people with tumors with higher glucose metabolism treated with metformin
No evidence of an effect
- No evidence of an effectoverall, one or more studies did not demonstrate that a treatment or intervention led to an expected outcome; this does not always mean that there is no effect in clinical practice, but that the studies may have been underpowered (too few participants) or poorly designed. Larger, well-designed studies provide more confidence in making assessments. on survival or tumor response among people with advanced or metastatic cancer (mostly with diabetes) treated with metformin in a combined analysis of studies
- No evidence of an effect on overall or progression-free survival among nondiabetic women with metastatic breast cancer treated with metformin
- No evidence of an effect on progression-free or overall survival among nondiabetic women with breast cancer treated with metformin in combined analyses of studies
- No evidence of an effect on overall survival or cancer-specific survival among people with breast cancer (not specific to diabetes) treated with metformin in combined analyses of studies
- No evidence of an effect on tumor proliferation among people with esophageal squamous cell carcinoma (not specific to diabetes) treated with metformin in a small study
- No evidence of an effect on progression-free survival and cancer-specific survival among women with stage 1–4 cervical cancer treated with metformin compared to people not treated with metformin, whether with diabetes or not, in a mid-sized study
- No evidence of an effect on survival or tumor proliferation among people with head and neck cancer (not specific to diabetes) treated with metformin in a several studies
- No evidence of an effect on risk of metastasis among people with lung cancer and diabetes treated with metformin in a preliminary study
- No evidence of an effect on overall survival or progression-free survival among people with lung cancer (not specific to diabetes) treated with metformin in combined analyses of studies
- No evidence of an effect on response rate or survival among people with diffuse large B-cell lymphoma treated with metformin in a preliminary study
- No evidence of objective response among nondiabetic people with melanoma treated with metformin in small studies
- No evidence of objective response among people with melanoma (not specific to diabetes) treated with metformin in small studies
Optimizing your body terrain
See MoreGood evidence of benefit
- Good evidencesignificant effects in one large or several mid-sized and well-designed clinical studies (randomized controlled trials (RCTs) with an appropriate placebo or other strong comparison control or observational studies that control for confounds) (this is the CancerChoices definition; other researchers and studies may define this differently) of lower body weight among nondiabetic people with cancer treated with metformin
- Good evidence of lower body weight among people with cancer (not specific to diabetes) treated with metformin for longer than 1 to 5 weeks
- Good evidence of lower levels of blood sugar among nondiabetic people with breast or endometrial cancer treated with metformin
- Good evidence of lower levels of many sex hormones among mostly nondiabetic people with cancer treated with metformin
- Good evidence of lower or more balanced markers of inflammation among people with cancer (not specific to diabetes) treated with metformin
Modest evidence of benefit
- Modest evidencesignificant effects in at least three small but well-designed randomized controlled trials (RCTs), or one or more well-designed, mid-sized clinical studies of reasonably good quality (RCTs or observational studies), or several small studies aggregated into a meta-analysis (this is the CancerChoices definition; other researchers and studies may define this differently) of lower body weight and waist circumference among people with metabolic imbalances other than diabetes treated with metformin
- Modest evidence of lower markers of insulin-like growth factors among people with cancer treated with metformin
- Modest evidence of higher levels of adiponectin—protective against insulin resistance/diabetes and atherosclerosis—among women with polycystic ovary syndrome (not specific to cancer) treated with metformin
- Modest evidence of lower levels of leptin—a hormone that suppresses appetite—among people with cancer treated with metformin
- Modest evidence of lower markers of inflammation among people with polycystic ovary syndrome (not specific to diabetes) treated with metformin
Preliminary evidence of benefit
- Preliminary evidencesignificant effects in small or poorly designed clinical studies OR conflicting results in adequate studies but a preponderance of evidence of an effect (this is the CancerChoices definition; other researchers and studies may define this differently) of lower body weight among nondiabetic people with endometrial hyperplasia without atypia treated with metformin
- Preliminary evidence of lower blood glucose after a meal but not while fasting among people with blood cancers without diabetes or prediabetes at baseline treated with metformin
- Preliminary evidence of lower insulin levels among nondiabetic people with colorectal cancer treated with metformin
- Preliminary evidence of lower levels of insulin or insulin resistance among people without cancer or diabetes treated with metformin
- Preliminary evidence of lower levels of insulin, insulin resistance, and/or blood sugar among overweight or obese people or with impaired glucose tolerance or insulin resistance treated with metformin
- Preliminary evidence of lower levels of insulin-like growth factors (IGF) among nondiabetic or mixed groups of people with breast or endometrial cancer treated with metformin
- Preliminary evidence of lower IGF-1 levels among nondiabetic people with major depressive disorder treated with metformin
- Preliminary evidence of lower levels of thyroid stimulating hormone among people with thyroid nodules and insulin resistance treated with metformin
- Preliminary evidence of lower markers of inflammation among nondiabetic people with major depressive disorder treated with metformin
- Preliminary evidence of a lower marker of oxidation among nondiabetic people with major depressive disorder treated with metformin
- Preliminary evidence of lower markers of oxidative stress during FOLFOX-4 regimen among people with colorectal cancer (not specific to diabetes) treated with metformin
- Preliminary evidence of changes in the composition of the microbiome, including beneficial increases in butyrate among among overweight or obese adults without medication-treated diabetes with solid tumor cancers treated with metformin
No evidence of an effect
- No evidence of an effectoverall, one or more studies did not demonstrate that a treatment or intervention led to an expected outcome; this does not always mean that there is no effect in clinical practice, but that the studies may have been underpowered (too few participants) or poorly designed. Larger, well-designed studies provide more confidence in making assessments. on a marker of glycemic control among men with normal glycemia and locally advanced prostate cancer treated with metformin in a small study
Managing side effects and promoting wellness
See MorePreliminary evidence of benefit
- Preliminary evidencesignificant effects in small or poorly designed clinical studies OR conflicting results in adequate studies but a preponderance of evidence of an effect (this is the CancerChoices definition; other researchers and studies may define this differently) of lower incidence of grade 3/4 neutropeniaan abnormally low number of neutrophils in the blood, leading to increased susceptibility to infection among nondiabetic women with metastatic breast cancer treated with metformin
- Preliminary evidence of short-term lower gains in body weight but no evidence of an effectoverall, one or more studies did not demonstrate that a treatment or intervention led to an expected outcome; this does not always mean that there is no effect in clinical practice, but that the studies may have been underpowered (too few participants) or poorly designed. Larger, well-designed studies provide more confidence in making assessments. on waist circumference among men with normal glycemia and locally advanced prostate cancer treated with metformin
- Preliminary evidence of better performance on tests of working memory and auditory-verbal memory, and a weak trendan apparent change due to a therapy, close to but not achieving full statistical significance (this is the CancerChoices definition; other researchers and studies may define this differently toward better reaction time, among survivors of pediatric brain tumors without insulin-dependent diabetes treated with metformin
- Preliminary evidence of lower incidence of nausea during chemotherapy among nondiabetic people with stage 4 non-small cell lung cancer treated with metformin
- Preliminary evidence of lower rate of grade 2 and 3 neuropathy, lower neurotoxicity scores, and other indicators of neuropathy during chemotherapy among people with colorectal cancer (not specific to diabetes) treated with metformin
- Preliminary evidence of lower scores of pain related to neuropathy during chemotherapy among people with colorectal cancer (not specific to diabetes) treated with metformin
No evidence of an effect
- No evidence of an effectoverall, one or more studies did not demonstrate that a treatment or intervention led to an expected outcome; this does not always mean that there is no effect in clinical practice, but that the studies may have been underpowered (too few participants) or poorly designed. Larger, well-designed studies provide more confidence in making assessments. on cognitive domain scores among overweight or obese postmenopausal women with breast cancer treated with metformin in a preliminary 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.
Modest evidence of benefit
- Modest evidencesignificant effects in at least three small but well-designed randomized controlled trials (RCTs), or one or more well-designed, mid-sized clinical studies of reasonably good quality (RCTs or observational studies), or several small studies aggregated into a meta-analysis (this is the CancerChoices definition; other researchers and studies may define this differently) of lower risk of cancer as a whole among people with diabetes treated with metformin
- Modest evidence of lower risk of recurrence among people with both bladder cancer and diabetes treated with metformin
- Modest evidence of lower risk of recurrence among people with urothelial cancer and diabetes treated with metformin
- Modest evidence of lower breast cancer-specific mortality among people without cancer at baseline with diabetes treated with metformin
- Modest evidence of slightly lower risk of breast cancer and lower breast cancer-specific mortality among people without cancer at baseline (not specific to diabetes) treated with metformin
- Modest evidence of lower risk of colorectal cancer among people with diabetes treated with metformin
- Modest evidence of lower risk of liver cancer among people with diabetes treated with metformin
- Modest evidence of lower risk of stomach cancer among people with type 2 diabetes treated with metformin, although with a risk of bias in studies that may contribute to overestimating the benefit
- Modest evidence of lower risk of gynecological cancers as a whole among people with diabetes treated with metformin
- Modest evidence of lower risk of cervical cancer among people with diabetes treated with metformin
- Modest evidence of lower risk of recurrence among diabetic people with endometrial cancer treated with metformin
- Modest evidence of lower risk of head and neck cancer among people with diabetes treated with metformin
- Modest evidence of a slightly lower risk of lung cancer among people with diabetes treated with metformin
- Modest evidence of lower risk of ovarian cancer among women with diabetes treated with metformin
- Modest evidence of lower risk of pancreatic cancer among people with diabetes treated with metformin
- Modest evidence of lower risk of recurrence among people with prostate cancer and diabetes treated with metformin
Preliminary evidence of benefit
- Preliminary evidencesignificant effects in small or poorly designed clinical studies OR conflicting results in adequate studies but a preponderance of evidence of an effect (this is the CancerChoices definition; other researchers and studies may define this differently) of lower risk of recurrence among diabetic people with hormone-receptor positive but not negative breast cancer treated with metformin
- Preliminary evidence of fewer grade 3 tumors or triple negative tumors, but higher incidence of ER or PR positive tumors, among people with breast cancer (not specific to diabetes) using metformin at the time of diagnosis
- Preliminary evidence of lower Breast Imaging Reporting and Data System (BIRADS)a reporting system used to describe the results of a mammogram, breast ultrasound, or breast MRI according to one of seven categories, ranging from normal or benign (not cancer) to highly suspicious or malignant (cancer) scores and positive pathological biopsy rate among overweight/obese premenopausal women without diabetes treated with metformin
- Preliminary (conflicting) evidence of slightly lower risk of esophageal cancer among people with type 2 diabetes treated with metformin
- Preliminary (conflicting) evidence of lower risk of recurrence among people with liver cancer (hepatocellular carcinoma) and diabetes treated with metformin
- Preliminary evidence of substantially longer recurrence-free survival among diabetic people with ovarian cancer treated with metformin
- Preliminary evidence of lower risk of recurrence among people with prostate cancer (not specific to diabetes) treated with metformin
No evidence of an effect
- No evidence of an effectoverall, one or more studies did not demonstrate that a treatment or intervention led to an expected outcome; this does not always mean that there is no effect in clinical practice, but that the studies may have been underpowered (too few participants) or poorly designed. Larger, well-designed studies provide more confidence in making assessments. on cancer-specific mortality among people at high risk of type 2 diabetes treated with metformin in a very large study
- No evidence of an effect on recurrence among people with breast cancer and diabetes treated with metformin in a combined analysis of studies
- No evidence of an effect on the percentage change in the number or size of colorectal and duodenal polyps among nondiabetic people with familial adenomatous polyposis treated with metformin in a preliminary study
- No evidence of an effect on markers of cell proliferation or cell death among nondiabetic people with Barrett’s esophagus treated with metformin in a preliminary study
- No evidence of an effect on recurrence among people with head and neck cancer without diabetes or mixed groups of diabetic and nondiabetic people treated with metformin in a combined analysis of studies
- No evidence of an effect on risk of recurrence among people with kidney cancer (not specific to diabetes) treated with metformin in mid-sized studies
- No evidence of an effect on risk of recurrence among people with acute lymphoblastic leukemia (not specific to diabetes) treated with metformin in a preliminary study
- No evidence of an effect on risk of recurrence among people with lung cancer and diabetes treated with metformin in a preliminary study
- No evidence of an effect on risk of lung cancer among people (not specific to diabetes) treated with metformin
- No evidence of an effect on risk of recurrence after treatment with paclitaxel plus carboplatin among people with epithelial ovarian cancer without diabetes treated with metformin
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.
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: April 19, 2024
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.