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Is Metformin a Miracle or a Menace?

The diabetes drug metformin makes new headlines. Some call metformin a miracle because of anti-aging, anticancer and anti-HIV/AIDS activity.
Is Metformin a Miracle or a Menace?
Metformin prescription pills with identification numbers on blue background ,image of a

The diabetes drug metformin has a lot of friends and foes. It never fails to amaze us when people try to either put a medicine on a pedestal or have the FDA ban it. Most drugs have both benefits and risks, pros and cons, plusses and minuses. Metformin is no exception. Why is metformin a miracle for some and a menace for others? There is growing interest in metformin for its anti-cancer, immunoregulatory and anti-aging activity. The latest research suggests it may even work against HIV/AIDS (Nature Immunology, March 25, 2021)

A Short Metformin History:

Metformin is the most popular diabetes drug in the world. Over 18 million Americans swallow it daily. Metformin is prescribed by itself or in combination with other blood glucose-lowering medicines. It is one of the most affordable medications for type 2 diabetes on the market.

Metformin really got its start centuries ago. That’s because during the middle ages European healers used the French lilac plant (Galega officinalis) to treat a wide range of conditions.

There are lots of popular names for Galega officinalis besides French lilac. It is also known as goat’s rue, galega, Spanish sainfoin, professor-weed or Italian fitch. It was used to treat symptoms that might have been caused by diabetes such as bladder problems, constipation, fluid retention (edema), blood disorders and fevers. In medieval times people also soaked their tired, sore feet in a goat’s rue solution.

Metformin for Modern Times:

Researchers discovered that this herb could lower blood sugar in animals in the 1920s. French regulators first approved metformin for the treatment of diabetes in 1957 under the name Glucophage (glucose eater).  It took US regulators much longer to consider metformin a miracle, if they ever did. The FDA gave the drug the green light in 1994.

Pharmaceutical manufacturers have developed a lot of pricey new medications to lower blood sugar. But metformin is still a mainstay, and researchers are exploring a number of new uses for this very old drug.

Metformin A Miracle against Cancer?

One of the more intriguing lines of research is metformin’s activity against cancer. Both laboratory and epidemiological research demonstrate that metformin has anticancer activity against a number of malignancies.

A review in the journal Oncology Reviews (online, Feb. 26, 2021) notes that:

“Many epidemiologic analyses have reported that metformin may improve prognosis of patients with different types of malignancies and even may prevent tumor initiation. Evans et al. noted as first that patients who were treated with metformin had a low risk of developing cancer. Next, a lot of studies in T2D [type 2 diabetes] patients have shown that metformin therapy is correlated with a reduced risk of numerous malignancies such as prostate cancer, lung cancer, head and neck cancer, breast cancer, pancreatic cancer, colorectal cancer, ovarian cancer and liver cancer.

“Among other things, there is also medical evidence that supports the benefits of metformin in patients with blood cancers. “

We suspect that if the drug were just discovered today, it would come with an enormous price tag and garner lots of attention. No doubt it would be regularly advertised on television. But metformin is dirt cheap because it is available generically.

Breast & Colorectal Cancer:

Two large population-based studies show that people who take metformin are less likely to develop breast or colorectal cancer (Diabetes Research and Clinical Practice, May 22, 2020). 

Melanoma, Endometrial & Bone Cancer:

A review of the medical literature reveals that metformin users appear protected in part from melanoma, endometrial cancer and bone cancer as well (Frontiers in Endocrinology, April 16, 2020).  In addition, the drug has benefits for the liver, the kidneys and the cardiovascular system.

Prostate Cancer:

Among more than 12,000 men with high-risk prostate cancer, the use of metformin in combination with a statin significantly reduced their risk of dying from prostate cancer (Cancer Medicine, April 2020).  Other investigators conducted test tube research showing synergistic effects of metformin and curcumin (the active ingredient in the spice turmeric). This combination helped put the brakes on prostate cancer cells (Nutrition and Cancer, July 13, 2020). 

A few other combination therapies also feature metformin. In one study of mice, scientists found that a combination of metformin with certain probiotics had beneficial effects on colorectal cancer (Cancers, July 10, 2020). 

Esophageal Cancer and Lymphoma:

Research suggests that metformin might also play a role against esophageal cancer and large B-cell lymphoma (Clinical Cancer Research, July 9, 2020; Cancer & Metabolism, July 6, 2020). 

Is Metformin a Miracle for PCOS?

Cancer is not the only condition for which metformin appears helpful. Women with polycystic ovary syndrome (PCOS) often have insulin resistance, even though they may not have type 2 diabetes. PCOS can affect fertility as well as quality of life, and metformin can help women with this condition ovulate (Fertility and Sterility, Sep. 2017). 

Is Metformin a Miracle for Longevity?

Anti-aging researchers are also looking at the potential for metformin to extend healthy life spans. Preliminary animal research has produced promising results (Cold Spring Harbor Perspectives in Medicine, March 2016). 

There are studies that suggest metformin doesn’t just help improve glucose metabolism. It reduces inflammation, helps reduce oxidative damage and diminishes cellular aging.

A review of the anti-aging activity of metformin offers this summary (Cell Metabolism, July 7, 2020)

“In conclusion, there is extensive epidemiological, basic science, and clinical data highlighting the effectiveness of metformin in targeting several age-related morbidities in humans. Studies in model organisms and cell lines provide compelling evidence on metformin’s beneficial effects against crucial pathways in aging.”

Metformin vs. HIV/AIDS:

A new study by researchers at the University of North Carolina at Chapel Hill suggests that metformin may slow replication of HIV in T cells (Nature Immunology, March 25, 2021). Instead of attacking the virus directly, metformin makes it harder for HIV to multiply inside cells. It does this by interfering with energy production.

It is always nice when experimental evidence is confirmed in a clinical setting. Although the research is preliminary, there is some suggestion that people with HIV who were taking metformin for their type 2 diabetes had substantially lower levels of HIV in their bloodstreams. This discovery may offer new insights into ways to treat HIV/AIDS.

The Dark Side of Metformin:

Despite all of the optimism about future uses for metformin, the drug has downsides.

Metformin Side Effects:

Digestive Tract Challenges:

  • Upset stomach (indigestion/heartburn)
  • Gas/flatulence
  • Diarrhea
  • Nausea/vomiting
  • Loss of appetite, metallic taste
  • Cramps



Liver toxicity


Lactic Acidosis:

More worrisome is lactic acidosis. Palpitations, rapid pulse, low blood pressure, lethargy and severe nausea/stomach pain could signal this rare medical emergency.

Metformin can also interfere with vitamin B12 absorption.

Metformin a Miracle? Not for These People:

We have heard from many visitors to this website that metformin caused serious complications:

Carol developed severe GI problems while taking metformin:

“I lost 40 pounds when on Metformin, and it caused such severe diarrhea that I couldn’t leave the house. Ultimately, a substitute doctor happened to see my records and called to tell me to stop taking metformin immediately and see a kidney specialist as soon as possible.”

Jackie also experienced serious side effects while taking metformin:

“I was prescribed metformin when I developed type 2 diabetes (after being put on statins due to family history of heart disease). I experienced severe diarrhea as well as swelling of feet and ankles and a severe itchy rash. Reported all side effects to doctor. Was told they would subside once my body got used to the medication. It never did.

“The doctor prescribed 800 mg ibuprofen 4 x day for swelling, sent me to dermatologist for rash, and told me to use OTC meds and learn to live with diarrhea.

“I was on metformin for about three years, until my kidneys began failing. Doctor sent me to kidney specialist who took me off metformin and all NSAIDS. My kidney function improved immediately, but I had to go on insulin. My question is: Why do doctors ignore warning signals clearly printed on prescribing literature and simply prescribe another risky medication to mask troubling (even dangerous) side effects?”

We suspect Jackie’s kidney problems resulted from the large dose of ibuprofen she took for three years. Even smaller doses can damage the kidneys.

Kay’s digestive problems kept her chained to her home:

“I started taking metformin to keep my blood sugar in the normal range because another med I was taking put my blood sugar thru the roof.

“I too suffered with continuous stomach upset and violent diarrhea. I could no longer leave the house safely without taking meds for the diarrhea. There were accidents. I tried it with food. I tried the slow release…..no help. Then my potassium started dropping.

“My doc prescribed another drug. It is low-priced and effective. After 6 weeks the diarrhea has stopped.

“There is no reason to take a drug that causes this many problems and chains you to your home. No responsible doctor should make you suffer. Change meds or change doctors.”

Greg developed lactic acidosis, a potentially life-threatening metformin complication:

“Metformin worked well for me, for about 10 years. It always caused me some stomach discomfort and flatulence. Then in November, 2016, I ended up in the hospital with severe vertigo and test results showing high levels of lactic acid. My doctor suspected lactic acidosis and took me off the drug. I’ve now found that none of the newer drugs work as well, and I’ve been started on insulin to get control of my blood sugar levels.”

So, Is Metformin a Miracle or a Menace?

It is neither. Like so many medicines, it can be beneficial for many and dangerous for others. You can learn more about metformin side effects at this link

Metformin (Glucophage) Side Effects & Complications
Metformin is a first line treatment for type 2 diabetes. It can be tough on the digestive tract. Could it also have anti-cancer activity and prolong life?

Sometimes old drugs can be repurposed for new conditions. The inexpensive drug metformin might be the best example of this principle.

If you would like to learn more about metformin as well as other approaches for treating type 2 diabetes, here is a link to our eGuide: Preventing & Treating Diabetes.

You will also want to read about metformin formulations that are not contaminated with nitrosamines at this link.

Which Metformin is OK and Which is on the FDA’s Problem List?
The FDA admits that several metformin diabetes formulations are contaminated with a probable carcinogen. Which metformin is OK? How would you know?

Share your own experience with metformin in the comment section below.

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About the Author
Joe Graedon is a pharmacologist who has dedicated his career to making drug information understandable to consumers. His best-selling book, The People’s Pharmacy, was published in 1976 and led to a syndicated newspaper column, syndicated public radio show and web site. In 2006, Long Island University awarded him an honorary doctorate as “one of the country's leading drug experts for the consumer.” .
  • Podhorecka, M, "Metformin - its anti-cancer effects in hematologic malignancies," Oncology Reviews, Feb. 26, 2021, doi: 10.4081/oncol.2021.514
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