blood sugar testing by pricking finger

This fascinating compound was discovered nearly a century ago. Scientists realized that it could lower blood sugar in an animal model (rabbits) as early as 1929 but it wasn’t until the late 1950s that a French researcher came up with the name Glucophage (roughly translated as glucose eater). The FDA gave Glucophage (metformin) the green light for the treatment of type 2 diabetes in 1994, 36 years after it had been approved for this use in Britain.
Glucophage lost its patent protection in the U.S. in 2002 and now most prescriptions are filled with generic metformin. This drug is recognized as a first line treatment to control blood sugar by improving the cells’ response to insulin and reducing the amount of sugar that the liver makes. Unlike some other oral diabetes drugs, it doesn’t lead to weight gain and may even help people get their weight under control.
Starting early in 2000, sales of metformin were challenged by a new class of diabetes drugs. First Avandia and then Actos tested metformin for leadership in diabetes treatment. Then Avandia lost its luster because of a link to heart attacks and strokes and now sales are miniscule because of tight FDA regulations. Actos is coming under increasing scrutiny as well. The drug has been banned in France and Germany because of a link to bladder cancer. The FDA has also required Actos to carry its strictest black box warning about an increased risk of congestive heart failure brought on by the drug.
This all means that metformin has regained its reputation as the best bang for the buck when it comes to type 2 diabetes management. The American College of Physicians has recommended metformin as the first line of treatment when lifestyle changes (diet, exercise and weight loss) have not led to adequate blood glucose control. That may be why nearly 50 million metformin prescriptions were dispensed last year.
Despite all the warm, fuzzy feelings about metformin for type 2 diabetes, there are some caveats. This drug does cause a number of side effects, especially when it comes to the gastrointestinal tract. They can be especially bothersome during the first few weeks of treatment. After several weeks, however, the digestive symptoms may fade away. If they recur, however, notify your doctor immediately as they could be symptoms of lactic acidosis (see below). Here is a list of adverse reactions to watch out for:


  • Heartburn
  • Stomach ache
  • Diarrhea
  • Gas
  • Headache
  • Nausea
  • Loss of appetite
  • Weakness
  • Rash
  • Lactic acidosis (symptoms may include irregular heart rate, nausea, stomach pain, lethargy, anxiety, low blood pressure and rapid heart rate) Notify your physician immediately if you notice any of these symptoms!

These side effects may seem daunting, but most people tolerate metformin quite well. The drug can be dangerous for people with kidney disease, however. They should not take the drug, and everyone on metformin should have their kidney function monitored regularly (at least once a year). People with congestive heart failure should not take metformin either.
There is an unexpected bonus to metformin therapy. There is growing evidence that this drug has an anti-cancer effect that may both prevent cancers from developing and spreading. In particular there are data suggesting that metformin may lower the risk of developing breast cancer, liver cancer, pancreatic cancer and colorectal cancer in people with diabetes and that the overall risk of developing cancer in such patients is substantially lower. More about this below.
A final word of caution, though. There are some nutritional consequences of metformin therapy. Here are some stories from readers. Please add your own comments about metformin treatment below theirs.

Q. I have read that metformin can cause a deficiency of Vitamin B12. I have not been able to find again the source of this information and would like your input.


A. This is from the prescribing information at DailyMed, identical to what is published in the PDR:

“Vitamin B12 Levels: In controlled clinical trials of metformin of 29 weeks duration, a decrease to subnormal levels of previously normal serum Vitamin B12 levels, without clinical manifestations, was observed in approximately 7% of patients. Such decrease, possibly due to interference with B12 absorption from the B12-intrinsic factor complex, is, however, very rarely associated with anemia and appears to be rapidly reversible with discontinuation of metformin or Vitamin B12 supplementation. Measurement of hematologic parameters on an annual basis is advised in patients on metformin and any apparent abnormalities should be appropriately investigated and managed (see PRECAUTIONS: Laboratory Tests).
Certain individuals (those with inadequate Vitamin B12 or calcium intake or absorption) appear to be predisposed to developing subnormal Vitamin B12 levels. In these patients, routine serum Vitamin B12 measurements at two- to three-year intervals may be useful.”

Q. My husband took metformin for years with no known side effects. Then his kidney functions started to deteriorate so he was seen by a specialist who immediately took him off metformin. He said that drug was very hard on kidneys and anyone who had any variations in kidney functions should not be taking it.
A. As mentioned above, kidney function must be monitored regularly to prevent just such a complication.

Q. I am suffering from such severe diarrhea I am sometimes afraid to leave the house. I also have bad gas and bouts of abdominal pain. I suspect the metformin I take for diabetes, but my doctor says my symptoms are not from my medicine.
The Prevacid I take for my heartburn isn’t helping enough to justify the expense. I am also experiencing pain and tingling in my toes.
A. Metformin (Glucophage) can cause diarrhea, nausea, heartburn, flatulence and stomachache. Acid-suppressing drugs like lansoprazole (Prevacid), omeprazole (Prilosec) or esomeprazole (Nexium) won’t solve the problem completely and may interfere with absorption of vitamin B12.
Metformin is also linked to reduced levels of vitamin B12. Because this vitamin is crucial for nerve function, deficiency can contribute to numbness, tingling or pain of the toes, feet or fingers, trouble walking, memory problems, depression, confusion and burning tongue.

The Miracle of Metformin

Before you give up on metformin because of side effects and scary stories, we want to tell you about some surprising benefits of this drug. There is growing evidence that metformin may have impressive anti-cancer activity. Not only does the drug seem to reduce the risk of developing a number of common cancers but it might reduce the spread of cancer once it is diagnosed.

Researchers are beginning to tease out one of the proposed mechanisms for the anti-tumor action of metformin, especially in prostate cancer. A study in the journal Prostate Cancer and Prostatic Diseases (Jul. 28, 2015) reported that effective treatment for aggressive or advanced disease is challenging. The researchers note:

“One potential target is the cancer stem cell (CSC). CSCs have been described in several solid tumors, including prostate cancer, and contribute to therapeutic resistance and tumor recurrence. Metformin, a common oral biguanide used to treat type 2 diabetes, has been demonstrated to have anti-neoplastic effects. Specifically, metformin targets CSCs in breast cancer, pancreatic cancer, glioblastoma and colon cancer.”

By exploiting a metabolic weakness in cancer stem cells, metformin theoretically makes these problem cells more vulnerable to conventional cancer therapies and could reduce the likelihood of cancer resistance and recurrence.

The Bottom Line

Metformin is an old diabetes drug that is being rediscovered for its potential role against cancer. Only time will tell whether it will live up to initial expectations. In the meantime, metformin remains one of the least expensive prescription drugs in the pharmacy. As long as people are vigilant about side effects and complications it could become one of the most intriguing drugs on pharmacy shelves. Here is a link to our article “Is Metformin a Modern Miracle Medicine?

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  1. Helen M
    Modesto, CA

    There are specific ways with which to begin metformin. Slow and slower for one! At the back end of your largest meal for another. That will usually eliminate most of the GI problems. So – you take 500mg after completing your largest meal. If you tolerate this, you begin to move the met thru your meal until you are taking it before you eat. I have read for maximum effect upon post meal numbers, it is best to take it a half hour before eating. I never remember. Then you do the same with your next largest meal. Some people see results on only a gram a day. Most people need more. Your options are to add an additional 500mg, same way until you are taking it before your meal. Then assess, do you need more? When do you want to take it?

    There are people who never adjust; they should try the timed release before giving up on the drug. It has a lot of benefits.

    As to kidney issues: Research has shown that people with impaired kidney function can do well with metformin too. However, the dose is related to the eGFR. I have one kidney, eGFR 53, started metformin two months ago. I am up to 1500mg a day, will have kidney tests next week. I took metformin for many years until I was diagnosed with cancer in both kidneys. My endo immediately removed the met and I had to increase my insulin by 50% and, once again, experienced problems with constipation. A lifelong condition that responded well to the met. This time that has not been true; however, I am taking more drugs with constipation as a side effect than I was the last time I was on met. More anti metabolic drugs too and I have not seen the decrease in insulin usage that I was hoping for. However, as a type 2 diabetic, diagnosed in 1983, I use very little insulin a day, about 21 units, and perhaps a further decrease, without changing other lifestyle factors, was not possible.

  2. Abigail

    There are several brands of Metformin. I switched to Amneal brand because the brand available through my HMO made me feel ill.

  3. Mary

    Dr. Richard K Bernstein, an 81-year old Type 1 diabetic, says to use the original glucophage and not the generics. He questions their effectiveness.

    And DO supplement with B12 or possibly along with all B vitamins. I have read that B1 deficiency is common with diabetes.

    Methylcobalamin is the most easily absorbed form of B12 per what I have seen online.

  4. Pat
    Dallas, TX

    I had been on Metformin since March 2010. I lost 20 lbs. in less than two months after starting the medication. It took a year for the next 10 lbs. It controlled my sugar up until May of this year. Having suffered with food allergies for over 30 years, I wasn’t surprised when my body started rejecting the Metformin. A pharmacist told me he was really surprised I couldn’t take it. He says doctors are prescribing it as a anti-aging pill today.

  5. Sylvia
    Waco, TX

    I gave taken Glucophage/Metformin for 12 years with great results. I tolerate it well, and my A1C is 6.0. I do take the extended release version of the drug, have lab work twice per year, maintain a healthy weight, and exercise daily.

  6. Elisabeth Meijer

    I experienced severe diarrhoea when on Metformin. At my request my doctor switched me to the extended release tablets and I no longer have diarrhoea.

    Many people have reported muscle pain, fatigue and memory loss as a side effect of Metformin. A number of prescription medications rob the body of CoQ10, and Metformin is one of them. Low levels of CoQ10 cause muscle pain, fatigue and memory loss. Consider taking CoQ10 capsules.

  7. Ann
    United States

    I have been taking Metformin about a year. 500 mg. (1/2 in A.M. and 1/2 P.M. with meals. Drink a ton of water. Since then I have quickly lost about 63 lbs. My sugar is very controlled. I really like Metformin. I do have alot of diarrhea but had that before the drug. Seems like everyone has a different experience with it.

  8. Tina
    United States

    I am not diabetic, but just suddenly stopped losing weight after changing my diet and becoming very active. I was put on glucophage about a week ago. I had some mild nausea the first 2 days, but I am experiencing a lot of gas and heartburn. I feel very bloated, and I am taking tums throughout the day

  9. Louis
    San Francisco

    I have been taking Metformin for a year now. Instead of declining, my sugar level rose from 150 to over 300 in a year, despite life style and dietary changes . After I take the medication, my blood pressure goes up to above 150 (Sys) and between 95 and 100 (DIA). I was better off without this drug.

  10. Carrie

    I have been on 1000mg of metformin for about 6 mths. I experience severe gas and rumbling in my stomach. The amount of gas by flatulence and burping is alarming. Sometimes my stools are complete water and gas. I’m getting concerned.

  11. Mindy

    I am newly diagnosed and put on Met. I thought I had the flu! I am so sick. I can’t go out for the diarrhea, I am totally nauseated, my back aches where my kidneys are, and I am hot and sweaty. I’m trying to diet and even though I can barely eat I’ve gained 4 lbs back of my 46 Lb loss. I read the side effects of this drug and I already suffer from : Depression, shallow breathing, and racing heart. Why would they put me on something like this my anti depressant already makes my stomach sick. They have never called me back today, the office is now closed. I am concerned the other drugs out there are not as safe as this and I’m not handling this!

  12. Dianna A.
    United States

    I have type 2 diabetes. I have been taking Metformin for 5 years. My doctor has increased dosage to 500mg three times a day. In the last year when I get to hot either playing golf or walking my dog my bp drops very low. I get really dizzy, heart beat increases and very weak. I have to sprinkle salt in my hand and eat it to get my bp back up. I also have days of severe diarrhea. I’m starting to adjust my dosage on days I very activity. I hope it helps.

    • Don

      I started out @ 2 doses of 500mg per day on metformin, then the doctor went to 3 times per day…in the beginning I had all the symptoms listed, & I asked & received doctor approval to break the pills in half, just keep up the dosage. I eventually became more tolerant of the drug, but exercise, diet are very critical to absorbing the pills properly. Finally I am at a point where I reasonably keep my sugar levels under control, most symptoms have been minimized.

  13. geraldine
    Upstate New York

    Have been on Metformin500mg for abt. 10 days . My blood pressure has dropped at least 20 points, and puts me in the low blood pressure range, and feel a little dizzy. Stay home until after lunch, then feel better.. Take Metformin with a meal. Will call my doctor on Monday (April 20th) This drop in bp is odd because I have a difficult time with my high blood pressure. Am on 3 meds for high blood pressure. Any one else have this reaction to Metformin? geraldine

  14. karl constantino
    Bethlehem, PA

    Terrible diarrhea. Insulin therapy is welcome

  15. karl constantino
    Bethlehem, PA

    I’ve had such bad diarrhea that insulin sounds sweet

  16. Valerie
    Edmonton, Alberta; Canada

    My mother had started taking Glucophage metformin in the mid 1990’s. In the summer of 2004, she phoned me, crying in pain, and saying that she was unable to walk. She rubbed her shins as she cried and told me she hurt there. I drove her to the hospital. To make a long story short, metformin destroyed her kidneys because she didn’t try to diet and lose weight. she liked snacking on sour cream with brown sugar, white bread, and KFC at least every now and then. I feel that because she didn’t work with the Glucophage metformin, it worked against her. My mother then started peritoneal dialysis, then several months later, was on hemodialysis. She passed away April 13, 2010.

  17. Sabrina
    San Diego

    A friend of mine told me that Metformin has caused significant hair loss for him. I have noticed too since I started taking it. I found nothing on your web site about it so I did a search and found this

    “One possible side effect of taking a medication called Metformin is hair loss. In fact, it is sometimes prescribed by doctors to treat patients suffering from a medical condition called hirsutism. This causes excessive hair growth and is often one of the unpleasant symptoms of PCOS or polycystic ovary syndrome.”

  18. lin

    Extended release metformin eliminated stomach pains and diarrhea symptoms. Please try this before other less safe meds.

  19. Habiba

    I’m not I diabetic , but I take metaformin for weight loss but not under a doctor supervision , I almost have all the side effects written above , but it really helps in controlling my appetite but I suffer conistently from nausea , is there any suggestions ?

  20. Paul

    I want to stop taking Metformin because of many issues others have described; I, too, have similar complaints; my concern is “going cold turkey,” so to speak and the health implications that may occur–I am one with Diabetes 2. I’d like some answers from those who have given up this toxic drug.

  21. Paul

    I’ve had problems that I believe are related to Metformin–severe digestive ones–watery stool, stomach pain, and a bloating sensation; the doctor I have doesn’t seem to believe my distress; I need to take a substitute for Metformin–a natural one–because I am determined as one with Diabetes 2 to stop taking this drug; I need to know of a natural substitute as I begin to go “cold turkey” with Metformin. Thanks.

    • Cee
      Upstate, SC

      Organic Apple Cider vinegar with the “mother” in it will help. Instructions are on the bottle distributed by Bragg

  22. Carolyn White
    Ben Wheeler, TX

    My husband has been on metformin for 6 years. And now he has renal cell carcinoma.

  23. Ms.Malone

    My, OBGYN prescribed me metformin because I was recently dx with pcos, which I don’t understand because my doc. didn’t really explain to me all he was thinking about my weight. I told him over an over it’s not my freaking fault- I can eat once daily, and not so much at that, and I will still gain 2 lbs. This is stressing me out taking out my hair I was once very beautiful my looks change hair growing on my chin I don’t have a family and would like to have one on my own. My OB told me to take 1500mg of metformin once daily and he said soon I will be pregnant, which is unbelievable! So hopefully this metformin helps me…

    • Elsie
      Puerto Rico

      My husband has been taking Metformin for about ten years, and after reading all of these comments I am worried, because he only has one kidney.

      • Ralph

        I have type 2 diabetes. Have taken metformin for 6 yrs. Was just released from the hospital after suffering from acute renal failure. My creatinine levels were at 5.7. I was taken off metformin and my numbers have come down. I also went to see a urologist during this time. After tests I am now beginning my fight with bladder cancer. I have become very anti-metformin. My blood, liver, and kidney functions were tested every 3 months. All were OK, then all of the above happened in a very short time.

    • Julie

      Eating only once a day is the worse thing you can do for your body. You need to eat at least 3 times (if not 5 times) a day. The thing to do is to think of them not as meals, but as snacks. Eat fruits and veggies, but also don’t forget to eat some kind of protein. Just keep is to small portions.

  24. Corryn

    Hey my name is Corryn and I have been taking mediformin for 6 months haven’t had much problem with it until I went up to 2000g a day. I have had a headache for 4 week now and I want to know will this go away or will I have to stop it ??

  25. Rosa

    Is it bad to stop metformin ? I have to many side effects.

  26. Rosa

    Glucophage causes me to cough all the time it does not stop, stomach pain, I’ve gone to Dr. for cough, taken medicine for it, does not work, when I stop taking glucophage my cough stops.

  27. Najal Sabir

    I have been diagnosed with diabetes 2 and have been taking metformin for almost two and a half months and I have not experienced any of these symptoms. I have lost 15 pounds which I needed to before I was constipated headache dry mouth, urinating constantly every time I was out and about was going every 30 minutes now all that have disappeared I take my medication at night. I exercise 30 minutes a day change my diet to mainly vegetables and protein and I feel great have a lot of energy. Before than didn’t.

  28. Katrina H.
    United States

    I was prescribed metformin for weight loss because I take an antipsychotic and it causes extreme hunger. I was excited after my first dose, my hunger went way down. I could look in the fridge and not even take anything! But I knew it was too good to be true, because it gave me severe bladder pain! I will not be able to continue this drug. I already have bladder issues (IC), and the metformin is really flaring up my bladder pain.

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