Metformin belongs to the class of medications called oral hypoglycemics, which are medications that lower blood sugar. It is used to control blood glucose (blood sugar) for people with type 2 diabetes. It is used when diet, exercise, and weight reduction have not been found to lower blood glucose well enough on their own.

Metformin works by reducing the amount of glucose made by the liver and by making it easier for glucose to enter into the tissues of the body. Metformin has been found to be especially useful in delaying problems associated with diabetes for overweight people with diabetes.

Your doctor may have suggested this medication for conditions other than those listed in these drug information articles. As well, some forms of this medication may not be used for all of the conditions discussed here. If you have not discussed this with your doctor or are not sure why you are taking this medication, speak to your doctor. Do not stop taking this medication without consulting your doctor.

Do not give this medication to anyone else, even if they have the same symptoms as you do. It can be harmful for people to take this medication if their doctor has not prescribed it.

The recommended adult dose of metformin ranges from 500 mg 3 or 4 times a day to 850 mg 2 or 3 times a day. The maximum daily dose should not exceed 2,550 mg daily. Tablets should be taken with food whenever possible to reduce the risk of nausea and vomiting. Metformin may be used alone or with other medications that reduce blood sugar. To ensure that the medication is working well, monitor your blood glucose on a regular basis as directed by your doctor or diabetes educator.

Many things can affect the dose of medication that a person needs, such as body weight, other medical conditions, and other medications. If your doctor has recommended a dose different from the ones listed here, do not change the way that you are taking the medication without consulting your doctor.

It is important that this medication be taken exactly as prescribed by your doctor. If you miss a dose, take it as soon as possible and continue with your regular schedule. If it is almost time for your next dose, skip the missed dose and continue with your regular dosing schedule. Do not take a double dose to make up for a missed one. If you are not sure what to do after missing a dose, contact your doctor or pharmacist for advice.

Store this medication at room temperature, protect it from light and moisture, and keep it out of the reach of children.

500 mg
Each white, round, biconvex, film-coated tablet, with blackberry scent, marked "MF" scoreline "1" on one side and "G" on the other, contains metformin HCl BP 500 mg. Nonmedicinal ingredients: blackberry flavour, macrogol, magnesium stearate, povidone, talc, and titanium dioxide.

850 mg
Each white, capsule shaped, biconvex, film-coated tablet, with blackberry scent, marked "MF2" on one side and "G" on the other, contains metformin HCl BP 850 mg. Nonmedicinal ingredients: blackberry flavour, macrogol, magnesium stearate, povidone, talc, and titanium dioxide.

Some medications may have other generic brands available. Always ask your doctor or pharmacist about the safety of switching between brands of the same medication.

Metformin should not be taken by anyone who:

• is allergic to metformin or to any of the ingredients of the medication
• is experiencing or recovering from severe infections, trauma, or surgery
• is pregnant
• is suffering severe dehydration
• is undergoing radiologic studies involving use of iodinated contrast materials
• drinks large amounts of alcohol in the short term or on a regular basis
• has diseases associated with lack of oxygen to the tissues such as cardio-respiratory insufficiency
• has reduced kidney function
• has severe liver disease
• has type 1 diabetes (they should always be using insulin)
• has very poor blood glucose control (they should not take this medication as the only anti-diabetic agent)

Many medications can cause side effects. A side effect is an unwanted response to a medication when it is taken in normal doses. Side effects can be mild or severe, temporary or permanent. The side effects listed below are not experienced by everyone who takes this medication. If you are concerned about side effects, discuss the risks and benefits of this medication with your doctor.

The following side effects have been reported by at least 1% of people taking this medication. Many of these side effects can be managed, and some may go away on their own over time.

Contact your doctor if you experience these side effects and they are severe or bothersome. Your pharmacist may be able to advise you on managing side effects.

• diarrhea
• loss of appetite
• metallic taste in mouth
• nausea
• passing of gas
• stomach ache
• vomiting
• weight loss

Check with your doctor as soon as possible if any of the following side effects occur:

• low blood sugar (mild), including:
  • anxiety
  • behavioural changes similar to being drunk
  • blurred vision
  • cold sweats
  • confusion
  • cool, pale skin
  • difficulty concentrating
  • drowsiness
  • excessive hunger
  • fast heartbeat
  • headache
  • nausea
  • nervousness
  • nightmares
  • restless sleep
  • shakiness
  • slurred speech

Stop taking the medication and seek immediate medical attention if any of the following occur:

• lactic acidosis (quick and severe), including:
  • fast, shallow breathing
  • muscle pain or cramping
  • slow or irregular heartbeat
  • unusual sleepiness
  • unusual stomach ache (after the initial stomach ache that can occur at the start of therapy)
  • unusual tiredness or weakness

Some people may experience side effects other than those listed. Check with your doctor if you notice any symptom that worries you while you are taking this medication.

Before you begin using a medication, be sure to inform your doctor of any medical conditions or allergies you may have, any medications you are taking, whether you are pregnant or breast-feeding, and any other significant facts about your health. These factors may affect how you should use this medication.

Alcohol intake: Anyone taking metformin should avoid excessive alcohol intake.

Blood sugar control: When a person taking metformin is exposed to fever, trauma, infection, or surgery, a temporary loss of blood sugar control may occur. At such times, it may be necessary to stop metformin and temporarily inject insulin. Metformin may be started again after the problem is resolved.

Blood sugar monitoring: Monitor your blood sugar regularly at intervals as discussed with your doctor or diabetes educator.

Diabetes complications: The use of metformin (or any other medication used for diabetes) will not prevent the development of complications peculiar to diabetes mellitus (e.g., kidney disease, nerve disease, eye disease).

Diet: Metformin is a treatment to be taken in combination with a proper diet. Metformin is not a substitute for proper diet.

Lactic acidosis: Lactic acidosis is a rare but serious problem that occurs due to metformin accumulation (i.e., the body doesn't get rid of it fast enough) during treatment. People with severe kidney disease are at higher risk of developing lactic acidosis. When it does occur (very rarely), it is fatal in 50% of cases. There have been no reports of lactic acidosis in Canada when metformin was used as directed.

Low blood sugar: Under usual circumstances, low blood sugar does not occur for people who take only metformin. Low blood sugar could occur when not enough food is eaten, especially when strenuous exercise is undertaken at the same time or when large amounts of alcohol have been consumed.

Reduced response: Over a period of time, people may become progressively less responsive to a particular treatment for diabetes because their diabetes worsens. If metformin fails to lower blood sugar to target levels, talk to your doctor. Your doctor may want to stop metformin or recommend another medication.

Pregnancy: This medication should not be used during pregnancy unless the benefits outweigh the risks. If you become pregnant while taking this medication, contact your doctor immediately.

Breast-feeding: Metformin is believed to pass into breast milk. If taking metformin is considered essential for the breast-feeding mother, your doctor will recommend that you stop breast-feeding.

Children: The safety and effectiveness of this medication have not been established for children.

There may be an interaction between metformin and any of the following:

If you are taking any of these medications, speak with your doctor or pharmacist. Depending on your specific circumstances, your doctor may want you to:

• stop taking one of the medications,
• change one of the medications to another,
• change how you are taking one or both of the medications, or
• leave everything as is.

An interaction between two medications does not always mean that you must stop taking one of them. Speak to your doctor about how any drug interactions are being managed or should be managed.

Medications other than those listed above may interact with this medication. Tell your doctor or prescriber about all prescription, over-the-counter (non-prescription), and herbal medications you are taking. Also tell them about any supplements you take. Since caffeine, alcohol, the nicotine from cigarettes, or street drugs can affect the action of many medications, you should let your prescriber know if you use them.