Oral blood sugar lowering drug.


Metformin (met-FOR-min) is used to treat a type of diabetes mellitus (high blood sugar) called type 2 diabetes. In this type of diabetes, insulin is produced by the pancreas but is not able to act on the cells of the liver, muscles and other tissues to make them take in the sugar and other food ingredients into the cells for its activities.

Metformin acts primarily in the liver, and to a lesser extent in skeletal muscles and other tissues, to increase the activity of insulin, thereby enhancing penetration of glucose into the cells, increasing storage or burning of glucose, and preventing formation of new glucose from stored products (glycogen) or other food substances like proteins and fats.

In contrast, Pioglitazone & Rosiglitazone act primarily in the muscles and to a lesser degree in the liver and other tissues, to achieve the same results as Metformin.

Since both the groups act on different enzyme systems, they may be co prescribed where needed.

These drugs do not help patients who are not producing any insulin, unless insulin is given as a supplement injection. This type is called insulin-dependent or type 1 diabetes. Their blood glucose is best controlled by insulin injections.

These drugs are available only with your doctor’s prescription, in the following dosage form:

Metformin Oral tablets: Tablets of 250 mg, 500 mg and 850 mg.

Before Using This Medicine

Your doctor needs to know some information about you before you are prescribed this drug. Tell him about the following:

  • Allergies–Any unusual or allergic reaction to metformin?  Also tell your doctor if you are allergic to any other substances, such as foods, preservatives, or dyes.
  • Pregnancy–No oral antidiabetic drug is recommended during pregnancy. If you are pregnant or contemplating pregnancy, you need to be on insulin for the duration of pregnancy, in the best interests of your baby. This is in spite of the fact that so far, metformin seems to be safe during pregnancy.
  • Breast-feeding–Metformin passes into breast milk. So far it has not been shown to cause problems in nursing babies.
  • Children–Due to ethical reasons, studies on this medicine have been done only in adult patients, and there is no scientific information comparing use of metformin in children with use in other age groups.
  • Adolescents–Due to ethical reasons, studies on this medicine have been done only in adult patients, and there is no specific information comparing use of metformin in teenagers with use in other age groups.
  • Older adults–Older patients may have moderate to severe liver or kidney disease or other contraindications to the use of metformin. Hence, it is generally to be avoided in late age groups.
  • Other medicines–Metformin interacts with many drugs and chemicals, whose simultaneous use must be done with caution if at all:
  • Alcohol–Small amounts of alcohol taken with meals do not usually cause a problem; however, either larger amounts of alcohol taken for a long time or a large amount of alcohol taken in one sitting without food can increase the effect of metformin. This can keep the blood sugar low for a longer period of time than normal

The following drugs may interfere with the excretion of metformin and lead to its overactivity and consequent low blood sugar:

  • Drugs that increase urine output like Amiloride,  Furosemide,  Triamterene
  • Drugs used to treat high Blood Pressure or heart disease like Calcium channel blocking agents (amlodipine, nifedipine, felodipine, lacidipine, etc), Digoxin, Procainamide, Quinidine
  • Drugs that reduce stomach acidity like Cimetidine, Ranitidine
  • Morphine (for severe pain)
  • Quinine (for malaria)
  • Antibacterial drugs like Trimethoprim, Vancomycin


The following conditions make it risky to use metformin because it may cause lactic acidosis, a condition where unregulated fat breakdown produces acids that can acidify the blood.

  • Acid in the blood (ketoacidosis or lactic acidosis) or ketones in urine
  • Moderate to severe burn
  • Severe water loss due to dehydration or diarrhea
  • During period of hormonal changes as seen during puberty, pregnancy, menstruation, overactive adrenal gland (Cushing’s syndrome)
  • High fever, severe infection, or injuries with marked tissue destruction, surgery, hear attack, tuberculosis
  • Mental stress (severe) or
  • Gut problems like severe inflammations of gut, slow stomach activity, vomiting, or any condition that upsets digestive system to a marked degree.
  • Moderate to severe diseases of vital organs like heart, blood vessel, kidney, liver, thyroid, adrenal gland, pituitary gland
  • Prior to use of certain drugs used for specific conditions : contrast agents for some types of X-rays
  • Severely malnourished or weakened patients

Many of these conditions lead to rapid blood sugar level changes : a condition best managed by Insulin Injections, till the crisis period is over.

Proper Use of This Medicine

Metformin should be used only under the supervision of your doctor, and will need to be taken for the rest of your life unless advised otherwise during specific periods as mentioned above. Metformin does not cure diabetes: only controls it; hence it must be continued even when you are feeling OK and your diabetes is under control. Even though it has side effects, the dangers of NOT taking this drug outweighs the small risks of taking it continuously.

The use of metformin does not in any way diminish the importance of a balanced regulated diet and exercise. You also need periodic evaluation and check up to avoid side effects and to maintain blood sugar levels at the desired level. In these matters, follow your doctors advice, especially :

  • When and how frequently to do Tests for Blood sugar.
  • Balanced Diet and fluid intake as per need (depends on age, sex, level of work, body weight, etc)
  • Exercise as per need and other conditions (heart disease, arthritis, asthma, etc)
  • When you are sick, the level of stress hormones rise, and they in turn raise blood sugar levels. Hence, please continue to take the regular dose of metformin, even if you feel too ill to eat. This is especially true if you have nausea, vomiting, or diarrhea, unless the doctor decides to stop metformin and switch you over to Insulin injections for some time. Contact your doctor for specific instructions, especially if severe or prolonged vomiting occurs .
    • Regularly and at frequent intervals, keep a check on your blood sugar and urine for ketones. If ketones are present, call your doctor immediately. Even when you start feeling better, let your doctor know how you are doing.

Dosing–There is no fixed dose of metformin. It depends on individual need, but is usually about 500 mg twice a day, up to a maximum of 3000 mg per day. If high doses are needed, it may be preferable to add a Insulin secretagogue drug or add insulin itself, since metformin cannot act in the absence of internal or external insulin.

Missed dose–If you miss a dose of this medicine, take it as soon as possible. However, if it is almost time for your next dose, skip the missed dose and go back to your regular dosing schedule.

Storage–To store this medicine:

  • Keep out of the reach of children.
  • Store in a cool dark place but not in a fridge.

Precautions While Using This Medicine

Your doctor will want to check your progress at regular visits , especially during the first few weeks that you take this medicine.

It is very important to follow carefully any instructions from your health care team about :

  • Alcohol–May cause very low blood sugar
  • Other medicines–Many drugs interact with metformin. Do not self medicate. If consulting many doctors, show all prescriptions to all doctors.
  • Counseling–Teach your family members to recognize side effects like low blood sugar, and what to do about it.
  • Seek a gynecologists opinion if planning for child. Women may need to be switched over to insulin during pregnancy and lactation.
  • Travel–Carry a copy of your recent prescription, brief disease history, and a small packet of glucose to use in case of sudden low blood sugar. Take you meal at usual meal times as far as possible.

Be prepared for an emergency:

  • Wear a locket or identification batch or keep a identification card in your wallet storing your disease details and drug history, including emergency medicines that should be given you in case you are unconscious or unable to communicate your needs.
  • Keep a small pouch / bottle of glucose handy to treat low blood sugar. Ordinary sugar is sucrose, which needs to be broken down to glucose and fructose, then absorbed and then work …… a needless waste of time.

As told earlier, tell any doctor you go to, about your intake of metformin, including a radiologist or pathologist. Many drugs for other conditions, and investigation procedures demand modification of blood sugar therapy.

Lactic Acidosis

Lactic Acidosis is the result of abnormal breakdown of sugars in the body, leading to excessive accumulation of lactic acid, which acidifies blood and may be fatal unless managed in time. Metformin does not cause lactic acidosis if used properly, as directed, avoiding precipitating conditions as mentioned above. The symptoms of lactic acidosis include : diarrhea, fast and shallow breathing, severe muscle pain or cramping, unusual sleepiness, severe vomiting and unusual tiredness or weakness. If you suspect this condition, drop everything and see a diabetes specialist at once, preferably in a hospital, as the management needs frequent checks and intravenous fluid therapy that no doctor on a house call is in a position to do, or should even be asked to attempt to do.

Symptoms of low blood sugar

  • Anxious feeling, behaving as if drunk, blurred vision, cold sweats, confusion, cool pale skin, difficulty in concentrating, drowsiness, excessive hunger, fast heartbeat, headache, nausea, nervousness, nightmares, restless sleep, shakiness, slurred speech, and unusual tiredness or weakness.

Causes of developing low blood sugar

  • Missing or markedly delaying a meal.
  • Excessive exercising
  • Too much alcohol.
  • Drug interaction (see above)
  • Illnesses like vomiting or diarrhea

Emergency measures for low blood sugar

  • Learn to recognize a  low blood sugar attack
  • Eat a fistful of glucose if available. Otherwise eat two or three table spoons of sugar or a glass of fruit juice or a table spoon of honey.

Side Effects of This Medicine

Rare Lactic acidosis
Low blood sugar
More common Loss of appetite; metallic taste in mouth; passing of gas; stomachache; loose motion, vomiting; weight loss