Who Should Be Taking Metformin Against Cancer?

Metformin was created in the 1920s by chemists who were working with the French lilac plant (Galega officinalis). That’s because healers had been using French lilac (aka goat’s rue) for centuries to control some of the symptoms of type 2 diabetes. Of course they didn’t know they were using this plant-based medicine for diabetes. All they did know was that it helped manage the thirst and frequent urination brought on by this metabolic disorder.

The drug was eventually marketed under the name Glucophage in 1957 in Europe. By the way, Glucophage is derived from the word glykys or glukus (glucose or sweet) and the word phagein (translated as eater or to eat). The French created the name glucophage to mean “glucose eater.”

It took the Americans more than three decades to get on board the metformin train. The FDA approved this interesting medication in 1994. It is available generically at a very modest price. At last count metformin was the second most prescribed drug in the United States, just after atorvastatin. Over 20 million Americans take it annually and that does not count diabetes drugs that contain metformin such as Glucovance, Janumet, Invokamet or Synjardy.

Metformin Against Cancer?

This reader wanted to know if this diabetes drug might be helpful against cancer.

Q. You’ve written that metformin helps keep cancer away. Then why doesn’t everyone take it? What are the side effects of this drug? Are the side effects serious enough to cancel the benefits of taking metformin if one is not diabetic?

A. Metformin is a pillar of type 2 diabetes treatment. Researchers have also discovered an anti-cancer effect of the drug in the breast, pancreas, liver, colon, ovaries and prostate (Experimental and Clinical Endocrinology & Diabetes, May, 2016).

Most doctors are understandably cautious about prescribing this drug for cancer prevention because more research is needed. This is an off-label use. The only approved use for metformin is in the treatment of type 2 diabetes.

More Anti-Cancer Research Involving Metformin:

The first reference we could find that metformin might have anticancer activity was published in the journal Gastroenterology, April, 2001. The researchers fed hamsters a high-fat diet plus a nasty carcinogen (N-nitrosobis-[2-oxopropyl]amine). Half the hamsters in the high-fat group developed malignant lesions, while none were found in the group that also received metformin.

Diabetes Drug Metformin in Cancer Prevention:

Scientists have been studying exactly how metformin can reduce the risk of various types of cancer. They are also considering how it might be used in conjunction with more conventional therapies to treat certain cancers (Morales & Morris, Annual Review of Medicine, 2015). In addition to colorectal and prostate cancers, researchers suggest that its ability to keep cancer cells from proliferating could be valuable in treating lung cancer (Gupta et al, Panminerva Medica, online Jan. 25, 2018).

They are even evaluating its usefulness in helping to treat glioblastoma multiforme, an aggressive brain cancer (Valtorta et al, Oncotarget, Dec. 2017). This medication suppresses cancer stem cells, including those from pancreatic, breast, colon and prostate cancers (Saini & Yang, Acta Biochimica et Biophysica Sinica, online Oct. 7, 2017).

Diabetes Drug Reduces the Risk of Head and Neck Tumors:

Researchers have reported that metformin may also offer benefits against head and neck tumors (Curry et al, The Laryngoscope, Aug. 2017). In this pilot study, the researchers took tissue samples from 39 patients with head or neck tumors. The participants then took metformin at about half the dose used by people with diabetes. The scientists sampled the tumors again and compared the metabolic markers.

How Does Metformin Fight Cancer?

Metformin interferes with cancer cells’ ability to create energy for growth by changing the pathways they use. Cancer cells are fast-growing, so they need a lot of energy generated quickly. The medication also encourages cancer cell death by disrupting the cancer-support system. Because metformin is generally well-tolerated and far less toxic than standard cancer drugs, it may become a valuable adjunctive treatment for a variety of tumors.

We have written previously about the diabetes drug metformin being used to fight cancer. You can read about it here and here.

Metformin Against Cancer…an Update:

A review of 31 studies concluded that “metformin exposure: reduced all cause mortality in colorectal cancer patients. The drug also improved cancer-specific mortality and overall survival.”

Another review published in Medicine, May 30, 2025, found that metformin:

“…can lower the fatality rates as well as incidence of breast, lung, liver, colorectal, and overall cancers.”

The authors call for large-scale randomized experimental studies to validate the results of their observational investigations.

The most recent research in JAMA Network Open, March 16, 2026 on esophageal cancer:

Researchers have analyzed data from five Nordic countries to compare 13,050 people newly diagnosed with esophageal squamous cell carcinoma to 130,500 healthy people of similar age and sex. Esophageal cancer is quite dangerous, with low survival rates.

The scientists report that people taking metformin had a 36% lower likelihood of being diagnosed with esophageal squamous cell carcinoma than those who were not. Higher doses were associated with even lower risk, about 48%.

The authors note:

“From a clinical perspective the observed association between metformin use and a significantly decreased risk of ESCC [esophageal squamous cell carcinoma] suggests a possible role of this drug in cancer prevention and treatment.”

What About Prostate Cancer?

There has been a fair amount of conflicting data when it comes to prostate cancer. The most recent study was published in BJC Reports (Feb. 3, 2026). The Australian researchers tracked over 94,000 men between 2005 and 2009. Over that time there were 5265 cases of prostate cancer.

The authors conclude:

“…metformin-use in obese as well as non-obese participants was associated with a lower risk of localised PC [prostate cancer]. Thus, metformin-use may lower the overall risk of PC diagnosis in non-obese participants however its use may not mitigate the adverse effect of obesity in the development of advanced PC.

“Further research could inform the repurposing of metformin for PC control.”

Side Effects:

Side effects can include digestive distress (diarrhea, nausea, vomiting, flatulence, indigestion, abdominal pain), rash, exhaustion and headache. Vitamin B12 levels can also be depleted and require supplementation.

The most serious, though rare, complication is lactic acidosis associated with failure of the heart and other organs.

Lactic Acidosis:

When people with type 2 diabetes have reduced kidney function they are at greater risk of lactic acidosis from diabetes drugs. It can also occur in healthy people when they exercise way too hard.

This condition is characterized by elevated blood lactate levels. Symptoms of lactic acidosis include:

• Confusion, cognitive impairment, anxiety, headache
• Fatigue, lethargy, sleepiness, weakness
• Digestive tract upset, poor appetite, nausea, vomiting,
• Rapid pulse, irregular heart rhythms, rapid breathing, sweating, clammy skin
• Sweet smelling breath

Lactic acidosis can lead to a life threatening crisis if not dealt with promptly. Kidney function testing is essential to prevent this kind of reaction. Dehydration adds to the problem so people on metformin should stay well hydrated.

To learn more about the unique benefits of metformin, check out these links:

Side Effects and Complications

Watch Vitamin B12 Levels!

Please share your metformin experience in comment section below. Has metformin been helpful for hurtful?