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Side Effects of Metformin (Glucophage, Formamet, Glumetza)

Updated on January 3, 2019
Sherry H profile image

Sherry Haynes is currently pursuing a PharmD degree and has experience in both the clinical and management sides of pharmacy.


Metformin hydrochloride is a low-cost prescription-only medicine prescribed to people with type 2 diabetes or, “adult-onset” diabetes.

Although it lowers blood glucose both between and after the meals it works differently from most other diabetes drugs. It decreases the amount of sugar released by your liver, reduces the absorption of glucose into the intestine and improves the body's response to insulin. Unlike other antidiabetes meds, Metformin does not cause your body to produce more insulin.

Brand Names

Metformin is available with various brand names from a variety of manufacturers around the world. But the active ingredient is the same metformin.

  • Glucophage
  • Glumetza
  • Formamet
  • Carbophage
  • Diabex
  • Gluformin

Common Side Effects

Like all blood-sugar-lowering medications, metformin can cause side effects in some patients. These effects are minor and usually occur during the first few weeks of metformin use.

Though the side effects may seem daunting, metformin is well tolerated by most patients. Taking metformin with meals generally reduces the side effects.

Later occurrence of these effects could be due to a serious side effect called lactic acidosis or other serious conditions. Talk to your prescriber if you don’t notice fewer problems with time. You may need to use a different medication for diabetes.

  1. Diarrhoea
  2. Nausea/vomiting
  3. Hypoglycaemia
  4. Flatulence
  5. Asthenia
  6. Indigestion
  7. Headache
  8. Abdominal pain
  9. Upset Stomach
  10. Ear pain
  11. Toothache
  12. Loose stools
  13. Tooth pain
  14. Sinus headache
  15. Muscle cramp
  16. Pain in limb
  17. Contusion
  18. Metallic taste in the mouth (in the initial days of metformin use)

Note: This is not a comprehensive list of side effects due to metformin. If you feel a lasting discomfort or pain talk to your pharmacist or/and doctor.

Hypoglycaemia due to Metformin

Metformin alone usually does not cause hypoglycemia although when this drug is used with other anti-diabetic drugs it can lead to low blood sugar. Hypoglycemia is more likely to occur with heavy exercise, drinking large amounts of alcohol, or not consuming enough calories from food.

Although these side effects are likely to go away notify your doctor if

  • You have severe discomfort.
  • These effects last for more than a few weeks.
  • These effects have started later during the therapy.

Serious Side Effects

Serious side effects are rare. The most serious side effect that metformin can cause is lactic acidosis, mainly in patients with kidneys and liver problem.

What is lactic acidosis

Lactic acidosis is the build-up of an acid in the blood. It is an emergency condition that should be treated in the hospital only. Lactic acid with metformin use will usually develop when you have other problems also.

You have a higher chance of getting lactic acidosis with metformin if you:

  • have severe kidney problems or your kidneys are affected by certain x-ray tests that use injectable dye.
  • have liver problems
  • drink alcohol very often, or drink a lot of alcohol in short-term "binge" drinking
  • get dehydrated (lose a large number of body fluids). This can happen if you are sick with a fever, vomiting, or diarrhoea. Dehydration can also happen when you sweat a lot with activity or exercise and do not drink enough fluids
  • concomitant use of certain drugs (e.g. carbonic anhydrase inhibitors such as topiramate)
  • have a heart attack, severe infection, or stroke
  • having a radiological study with contrast, surgery and other procedures

The Following Symptoms Could be a Sign of Lactic Acidosis. Call Your Doctor Immediately if

  • You feel cold in your hands or feet
  • You feel dizzy or lightheaded
  • You have a slow or irregular heartbeat
  • You feel very weak or tired
  • You have unusual (not normal) muscle pain
  • You have trouble breathing
  • You feel sleepy or drowsy or anxiety
  • You have stomach pains, nausea or vomiting

What You Should Tell Your Doctor When You are Prescribed Metformin

Tell your doctor if

  • You have severe kidney problems or liver problems.
  • You drink alcohol very often or binge drink.
  • You are going to go for an X-ray
  • You are going to go for surgery.
  • You have any other medical conditions.
  • You are on other medications or herbal supplements.
  • You are pregnant or plan on becoming pregnant.

Drug and Food Interactions

Metformin like many other medications can interact with many prescription and over-the-counter medications as well as herbal supplements. To prevent them all you need to do is tell your doctor about the prescription and non-prescription medicines, vitamins and herbal supplements you are taking currently. And remind your doctor and/or pharmacist that you are on metformin when any new drug is prescribed to you.

My Blood Sugar is Still too High Even After Taking Metformin

If your blood sugar is high, consult your doctor. Your doctor may increase the dose or prescribe you another medication, generally a sulfonylurea if your body does not respond to the maximum dose of metformin after waiting for a few weeks. If it still does not respond he may change to a medication from another class of diabetes drugs. If it's still too high, he may prescribe you injectable insulin.

I am Prescribed Metformin with Another Diabetes Medication

Depending on how your body responds to metformin therapy your doctor may add another diabetes medication, generally a sulfonylurea. The additive effect of both drugs will lower your blood sugar. Monitor your blood glucose regularly to avoid an abnormal decrease in the glucose level. Doctors treat each patient individually and he or she should follow all the treatment recommendations.

I am Prescribed Metformin While I am on Insulin Therapy

Adding metformin to insulin can help you better control your blood sugar while reducing the insulin dose and possibly reducing your weight. Your doctor may prescribe you metformin as an addition to insulin therapy. Initially, you may be prescribed a low dose of metformin which may then be increased depending on your body’s response. Monitor your blood glucose regularly and inform your doctor if the fasting blood glucose goes below 120 mg/dl. Each patient will be treated individually by his or her physician and should follow all the treatment recommendations.

My Diabetes Medication is Changed From Chlorpropamide to Metformin

Monitor your blood glucose levels closely during the first two weeks of being prescribed metformin. Since chlorpropamide remains in the blood for a long time, the additive effect of both the diabetes drugs can cause your blood sugar to go too low.

Patient Information

1. Take the metformin tablet whole immediately after meals. The metformin tablets (or any other tablet) that come as extended-release should never be crushed. These tablets are meant to release the active ingredients in an extended period of time so crushing the tablet defeats the purpose. XR or SR will be returned on the label of these tablets beside the generic name.

2. Monitor your blood glucose and glycosylated haemoglobin regularly. Test your kidney and liver function at least once a year.

3. Right diet and exercise for diabetes patients are as important as diabetes medications.

4. Up to 30% of patients on metformin may develop the deficiency of vitamin B12.
An oral dose of 1mg/day of vitamin b12 may be sufficient to overcome the deficiency in two weeks. Thereafter 1 mg/month should maintain adequate levels of cobalamin.


  1. Bray G.A., Edelstein S. L., Crandall J.P., Aroda V.R., et al. (2012) Diabetes Prevention Program Research Group Long-term safety, tolerability, and weight loss associated with metformin in the Diabetes Prevention Program Outcomes Study. Diabetes Care, 35(4), 731–737.
  2. Salpeter S, Greyber E, Pasternak G, Salpeter E. (2006) Risk of fatal and nonfatal lactic acidosis with metformin use in type 2 diabetes mellitus. Cochrane Database Syst Rev. 1:CD002967.
  3. Scheen AJ, Paquot N. (2013) Metformin revisited: A critical review of the benefit-risk balance in at-risk patients with type 2 diabetes. Diabetes Metab. 39, 179–90.
  4. Baradaran A. (2012). Lipoprotein (a), type 2 diabetes and nephropathy; the mystery continues. J Nephropathol. 1,126–9.
  5. Scheen AJ. (2011) Metformin and lactic acidosis. Acta Clin Belg. 66, 329–31.
  6. Nasri H, Behradmanesh S, Maghsoudi AR, Ahmadi A, Nasri P, Rafieian-Kopaei M. (2014) Efficacy of supplementary vitamin D on improvement of glycemic parameters in patients with type 2 diabetes mellitus: A randomized double blind clinical trial. J Ren Inj Prev. 3, 31–4.

© 2019 Sherry Haynes


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    • Eurofile profile image

      Liz Westwood 

      21 months ago from UK

      In the UK diabetes is increasingly being diagnosed. The most at risk groups appear to be the overweight and the elderly. This is therefore an interesting and useful article.


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