french lilac flowers

Q. My doctor recently suggested that I should start taking metformin to help prevent a recurrence of prostate cancer. When I looked the drug up online I discovered that it is prescribed for diabetes. My blood sugar is fine. Why would this drug work against cancer? Won’t my blood sugar drop too low and get me into trouble with hypoglycemia? What other side effects should I know about?

A. One of the most successful diabetes drugs ever discovered originated from folk medicine. French lilac (Galega officinalis), also known as Italian fitch or professor-weed, had been used for centuries by native healers to help control elevated blood sugar. French researchers found in the 1920s that the active compound could lower blood sugar in an animal model (rabbits).

It took until the 1950s to verify that metformin really worked to control diabetes in humans. The FDA approved metformin for sale in the United States in 1994 under the name Glucophage (glucose eater in French). The drug works by enhancing our cells’ response to insulin, thereby improving blood sugar control. Because it is available generically it is inexpensive, making it one of the best deals in diabetes management.

In direct response to your question, metformin is less likely to cause low blood sugar (hypoglycemia) in people with type 2 diabetes than many other drugs. Symptoms to be alert for, though, include dizziness, shakiness, cognitive dysfunction, confusion, headaches, fast pulse, pale skin and hunger. Although hypoglycemia is an unlikely complication, you may want to ask your doctor whether it would be helpful to monitor your blood sugar levels to make sure that they don’t drop too low.

Metformin’s Anti-Cancer Benefits

Evidence continues to mount that metformin may help prevent a number of cancers from developing or if they do, from spreading throughout the body. Here is just a partial list of cancers that may be inhibited by metformin:

  • Breast Cancer
  • Colorectal Cancer
  • Liver Cancer
  • Lung Cancer
  • Pancreatic Cancer
  • Prostate Cancer

Here is a quick summary of some fascinating prostate cancer research: A study of Canadian men with diabetes and prostate cancer suggested that those taking metformin were less likely to die of this malignancy than men taking other diabetes drugs. The study lasted nearly five years. [Journal of Clinical Oncology, online August 5, 2013]

A study of men in Taiwan found that those with diabetes who were treated with metformin had a decreased risk of developing prostate cancer [European Journal of Cancer, online, Sept. 5, 2014]

Another study found that prostate cancer cells may be less likely to progress and metastasize if metformin is on board. [Biochemical and Biophysical Research Communications, online, Sept 6, 2014]

As exciting as the potential benefits of this drug may be, there are side effects to be aware of. Do pay attention to some potential complications.

Metformin Side Effects

  • Digestive distress including stomach upset, gas, nausea, indigestion, diarrhea
  • Loss of appetite
  • Headache
  • Weakness
  • Rash
  • Low levels of vitamin B12 (supplements are often required to prevent a deficiency)

Lactic acidosis

This adverse reaction is relatively rare but could be quite serious if it develops. Notify your doctor immediately if you develop any of the following:

  • Irregular heart rhythms or rapid pulse
  • Lethargy
  • Anxiety
  • Low blood pressure
  • Serious nausea and stomach pain

You can learn more about diabetes treatments in our Guide to Managing Diabetes. Share your own experience with metformin below.

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  1. Robert
    NH USA

    During my research of French lilac the source for Metformin, I noticed two things lactic acidosis and B1 deficiency. Both kept popping up in almost every article I read. What is the connection?

  2. Rahulan
    Balikpapan, Indonesia

    The best diagnosis of any kind of symptom is the person who suffers it so self diagnosis is the best.

  3. Elizabeth
    Buffalo, NY

    Would giving up sugar be just as effective as Metformin at starving energy-hungry cancer cells? (With the added benefit of probable weight loss and no side effects after initial sugar withdrawal symptoms?)

  4. cpmt

    Are they any options to replace metformin? and if not any other medicine to prevent kidney damage?

  5. LCF

    My husband was on Metformin for years. His health was failing, he was shaking and sweating at the same time. After a very bad episode, several tests were done and showed he had kidney problems. The kidney specialist immediately took him off Metformin and warned him never to take it again. Apparently, over time, it can severely damage your kidneys — something no one every told us about.

  6. Ed

    Metformin also interferes with vitamin B12. Vitamin B12 deficiency can have debilitating consequences. People taking Metformin should have have their B12 and homocysteine levels checked periodically.

  7. KT556
    Chicago suburb

    SIDE EFFECTS: should be EXPLOSIVE diarrhea — in all too many cases!

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