Can Metformin Treat and Prevent Cancer?

Recently, a New York Times article was published that caught my attention. The article exposed a possible link between sugar intake, high glucose and insulin levels, and cancer. According to the article, sugar may fuel cancer cells, promoting tumor growth. Dr. James Watson, one of the fathers of molecular biology who was interviewed for the NY Times article, revealed that although he doesn’t have cancer, he electively takes metformin to prevent cancer. Why metformin? It’s simple: metformin works to reduce blood sugar levels in the body. There is even some research that shows that metformin can not only prevent cancer but help treat it as well. This is certainly good news for those who have PCOS and take metformin.

Sugar and Cancer Link

Sugar may be a driving force in cancer progression. Metabolism-centered cancer theories imply that cancer cells are addicted to food and nutrients, especially sugar, which fuels tumor growth. If cancer cells are starved of nutrients, they start to die.

Insulin is known for promoting fat storage also known as weight gain. Insulin’s primary role is to push glucose into cells to be used for energy. According to the Insulin Hypothesis, insulin triggers tumors to grow awry by signally cancer cells to take up more glucose. In this theory, more glucose means more cancer growth. There is research that suggests that many people who develop colorectal, pancreatic or breast cancer had elevated insulin levels before their diagnosis. Scientists who gave insulin to breast tissue found that it promoted tumor growth; when they removed the insulin, the cancer cells died.

A Limit on Sugar

The US Dietary Guidelines recommend our sugar intake be no more than 10% of our total calories, in part to reduce our risk for chronic diseases like cancer. For someone eating 1,800 calories, that’s no more than 45 grams of sugar daily (or 12 teaspoons of table sugar). That’s about the amount in one 16-ounce bottle of soda.

The American Heart Association has stricter guidelines, stating sugar intake should be limited to 100 calories (25 grams, or 6 teaspoons) per day for women, and to 150 calories (about 37 grams, or 9 teaspoons) per day for men.

Currently, the average sugar intake in America is 88 grams, or 22 teaspoons of added sugars each day – a 20% increase over the past three decades. The proposed revised food label, set to debut in July 2017, plans to list a separate line for added sugars, making it easier to know how much sugar a food has.

Metformin’s Role in Treating Cancer

Metformin is the most widely prescribed medication to individuals with type 2 diabetes. According to the New York Times article, 76.9 million prescriptions for metformin were filled in the United States in 2014. Although it’s not FDA approved, metformin is also one of the most commonly prescribed medications to women with PCOS for insulin resistance.

Because of its role in lowering glucose and insulin levels, metformin has gotten the attention of researchers as a way to treat or even prevent cancer. Today more than 100 randomized controlled trials of metformin and cancer are currently registered at People with diabetes who take metformin are significantly less likely to develop cancer than people with diabetes who don’t take metformin. Those with diabetes who do develop cancer and take metformin, are less likely to die from it.

Research published  this week showed that metformin may help women with endometrial hyperplasia, a condition common in women with PCOS who have thickening of the endometrial lining due to a hormone imbalance, and which increases the risk for uterine cancer. Women who were given metformin showed a 56% resolution of the hyperplasia. The effect was seen especially in women with simple hyperplasia without additional complications or irregularities.

Despite the potential, metformin as an anti-cancer treatment drug remains controversial. The timing of when metformin is used may make a difference as well. Researchers from the University of Pennsylvania just reveled the first survival results using metformin in women with breast cancer. In their study, they looked at 1,215 patients who were diagnosed and underwent surgical treatment for breast cancer between 1997 and 2013. Ninety-seven patients examined reported using metformin before their diagnosis, and 97 reported use of the drug after diagnosis. The good news was that those patients who were given metformin after being diagnosed with cancer were almost 50% more likely to survive than those who didn’t take metformin. The bad news: patients who were already taking metformin when diagnosed were more than twice as likely to die than patients who never used the drug. Why the difference? According to lead author Yun Rose Li, MD, PhD, a clinical research fellow in the division of Endocrine and Oncologic Surgery at the Perelman School of Medicine at the University of Pennsylvania, “those who developed breast cancer while already using Metformin may have more aggressive cancer subtypes.”

Bottom line: Metformin is showing promise as an anti-cancer medication and could potentially be one factor used on the war against cancer. Much more research needs to be conducted to determine metformin’s role in cancer treatment or prevention. As a reminder to followers of the PCOS Nutrition Center blog, Metformin can cause a deficiency in vitamin B12. Those who take metformin should have their levels of B12 checked annually.

To reduce your cancer risk right now, eat a diet rich in fruits and vegetables and fiber. Limit red meat. Include small amounts of sugar. Don’t smoke. Get regular physical activity. And enjoy life.


Goodwin P. Metformin, Cancer Risk, and Prognosis. American Society of Clinical Oncology. 2011;1092-9118/10/1-10.

Metformin for cancer prevention: a reason for optimism. Lancet Oncol. 2016;2045(16)00006-1.

Emily Meichun Ko MD, MSCR. Metformin for the treatment of endometrial hyperplasia. J Clin Oncol 34, 2016 (suppl; abstr 5592). American Society of Clinical Oncology ASCO Annual Meeting, Chicago, IL June 6 2016.

Yun Rose Li. The impact of long-standing metformin use on survival in breast cancer patients. J Clin Oncol 34, 2016. American Society of Clinical Oncology ASCO Annual Meeting, Chicago, IL June 6 2016.

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Comments (4)
  • Jill

    November 3, 2018 at 2:06 pm

    There is a push in great Britain to make metformin[I would take berberine], mebendazole[PINWORM medication], a statin and doxycycline for cancer as a go to treatment. Clearly some people don’t need need another study!

  • Peggy Brooks

    October 11, 2020 at 9:05 am

    They said on the news Friday, Oct 9th that Metformin causes cancer, is that true? I’ve taken it for years.

  • Angela Grassi

    November 3, 2020 at 9:47 am

    Metformin itself does not cause cancer. If anything, it can help prevent and treat cancer. The problem is the FDA identified some types of extended release versions to have cancer causing ingredients. Check with your pharmacy.

  • Jerry Way

    July 27, 2021 at 4:37 pm

    interested in Metformin hcl 850 Mg tabs, 2 x day with meals?

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