Metformin - Use | Dose | Side Effects

This article was medically reviewed by M.Pharm, Marko Tanaskovic on August 12, 2018. To read more about an author, click here.

Metformin is a drug that is classified according to the pharmacological characteristics in the oral anti-diabetic agents while according to its chemical characteristics it is classified as biguanides. It works by decreasing the glucose synthesis in the liver1 and increasing the muscle sensitivity to the insulin, but not stimulating the insulin secretion. Because of this mechanism of action, this drug rarely causes hypoglycemia unlike other anti-diabetic drugs.

Metformin is used only for the treatment of diabetes mellitus type 2 and is the drug of choice for diabetes treatment. Clinical studies have shown that this drug reduces the risk of complications in patients with diabetes (e.g. nephropathy and retinopathy).


Metformin can cause lactic acidosis2,3,4 - a condition characterized by an increase in the level of lactic acid in the blood. If you notice any symptoms of lactic acidosis (e.g. nausea, vomiting, chills, blue-colored skin, irregular heartbeat or shortness of breath), call your doctor immediately. Lactic acidosis is a side effect that occurs very rare due to the use of Metformin (only 1 in 10 000 patients experiences this side effect), but because of its severity it is necessary to know what are the symptoms. You should call your doctor as soon as possible if any of the symptoms occur. Lactic acidosis is best treated by hemodialysis.

Lactic acidosis occurs more frequently in patients who have liver or kidney impairment, and the use of Metformin in such patients should be carefully implemented. The use of large doses of this medications is associated with higher risk for lactic acidosis occurrence.

As already mentioned, Metformin rarely causes hypoglycemia, if used individually. Co-administration with other anti-diabetic medicines increases the risk of hypoglycemia. The risk of hypoglycemia is higher in patients who eat less and exercise more.

Metformin commonly causes digestive problems (abdominal pain, nausea and diarrhea), but these side effects usually resolve after a few days.

Metformin, pregnancy and breastfeeding

Clinical studies have shown that Metformin is safe for the treatment of gestational diabetes (a form of diabetes that occurs during pregnancy).2 The American Society for Endocrinology recommended this drug as a first-line medication for the prevention of complications during pregnancy. However, there are no guidelines what dose should pregnant women take and for how long. Some researches suggest that Metformin should not be used during the first three months of pregnancy and that in this period it is better to use other anti-diabetic medications (insulin and glyburide, for example).

In clinical studies, use of Metformin in pregnant women who have polycystic ovary syndrome, reduced the risk of premature birth and miscarriage.

It should be cautiously administered to nursing mothers, because it is excreted into the breast milk.


The dose depends on the blood glucose levels. The starting dose is usually 500 mg 2 or 3 times a day and may be increased two weeks after starting the therapy, if there is need to.

Metformin works best if taken during a meal or immediately after a meal.

It should not be used in children younger than 10 years.

The maximum daily dose is 3 grams.

If you're taking this medicine once a day, it is best to take it with breakfast. If you're taking this medicine twice a day, then it is best to take it with breakfast and dinner. If you're taking this medicine three times a day, you should take it with breakfast, lunch and dinner.


Metformin enter in major interactions with the following drugs:

  • Diatrizoate and metrizamide (contrast agents for X rays)
  • Iothalamate, iodixanol, iopamidol and ioversol (radiocontrast agents)
  • Fluorochinolone antibiotics (e.g. gatifloxacin). Co-administration of these drugs increases the risk of hypoglycemia

Metformin can also enter into interactions with the following medications:

  • Anti-asthmatics (e.g. salbutamol)
  • Corticosteroids
  • Diuretics

Adverse effects

Possible side effects of the Metformin include:

  • Nausea, vomiting, abdominal pain, diarrhea and other stomach problems (these occur very often)
  • Taste changes (occurs often)
  • Lactic acidosis
  • Megaloblastic anemia (occurs because Metformin reduces the absorption of vitamin B12)
  • Hepatitis


  1. NCBI link 1
  2. NCBI link 2
  3. NCBI link 3
  4. NCBI link 4

Information on this website are provided for educational purposes only and are not intended for medical advice, diagnosis or treatment.

If you have any concerns or questions about your health, you should always consult with a physician or other health-care professional.

We and our partners use technology such as cookies on our site to personalise content and ads, provide social media features, and analyse our traffic. Click below to consent to the use of this technology across the web. You can change your mind and change your consent choices at anytime by returning to this site.