Updated 11 February 2013


Metformin is an oral blood-glucose-lowering drug.


Metformin is the active ingredient of Arrow Metformin, Austell-Metformin, Bigsens, Forminal, Glucophage, Metforal and Sandoz Metformin.

Metformin is also one of multiple active ingredients found in Glucovance (metformin + glibenclamide).

General information

Metformin is an oral blood-glucose-lowering drug. It is prescribed in the treatment and management of type 2 diabetes (a disease caused by a problem in the way the body makes or uses insulin, which is necessary for glucose to move from the blood to the inside of the cells) that is not adequately controlled by diet and exercise alone.

Type 2 diabetes makes up 90 per cent or more of all cases of diabetes.

Treatment with oral anti-diabetic drugs should only be started once all lifestyle and dietary measures have been tried for at least three months and have not controlled blood glucose adequately. Once treatment with this medication is started, diet and exercise should however not be stopped.

Metformin is the oral anti-diabetic drug of choice in overweight type 2 diabetics. It induces mild loss of appetite and thereby helps to control weight.

Metformin can be used on its own - and treatment is often started with one drug only - or in combination with other oral blood-glucose-lowering drugs.

For metformin to remain effective, it needs to be taken regularly.

Lactic acidosis (high levels of lactic acid in the blood which may be fatal) is a potential, but rare side effect seen with the use of metformin. The use of alcohol while being treated with metformin increases the risk of lactic acidosis.

Generally, this medication is used when the body is still producing some insulin.

How does metformin work?

Metformin reduces the amount of glucose supplied by the liver, and also enhances the uptake of glucose in muscles. It furthermore reduces the absorption of glucose from the digestive tract into the bloodstream.

Fast facts

Drug schedule: schedule 3

Available as: metformin is available as tablets

What does it do? metformin lowers blood sugar

Overdose risk: high

Dependence risk: low

Is metformin available as a generic? no

Is metformin available on prescription only? yes

User information

Onset of effect: within 2 hours

Duration of action: up to 15 hours

Dietary advice: metformin should be taken with meals to reduce gastrointestinal side effects

Stopping this medicine: consult your doctor before stopping this medication; diabetes may worsen with premature discontinuation

Prolonged use: long-term use may lead to anaemia as a result of vitamin-B12 depletion

Special precautions

Consult your doctor before using this drug if:

  • you have congestive heart failure
  • you have kidney or liver disease
  • you have a history of alcohol abuse
  • you are taking other medication

Pregnancy: avoid. Potential risk to the foetus has been reported. Consult your doctor before use, or if you are planning to fall pregnant.

Breastfeeding: avoid. This medication is passed through breast milk and may affect your baby adversely. Consult your doctor before use.

Porphyria: safe to use.

Infants and children: this medication is not intended for use in children.

The elderly: caution is advised in the elderly as adverse effects are more likely.

Driving and hazardous work: caution is advised as use of this medication may lead to dizziness or light-headedness. Avoid such activities until you know how this medication affects you.

Alcohol: avoid concomitant use of alcohol with this medication.

Possible side effects

Side effect


Consult your doctor



Only if severe

In all cases

loss of appetite



metallic taste in mouth



nausea/ vomiting












abdominal bloating



rapid shallow breathing



unusual sleepiness/ weakness



rapid pulse



blurred vision







Drug interactions


increased risk of lactic acidosis


increased risk of metformin toxicity


may diminish effect on blood sugar


may diminish effect on blood sugar

Disease interactions

Consult your doctor before using this drug if you have congestive heart failure, kidney or liver disease or if you have a history of alcohol abuse.

Overdose action

An overdose of this medication can be serious. Seek immediate emergency medical attention.

Recommended dosage

Adults: 500mg three times daily, or 850mg twice daily. Maximum dose is 3000mg/day.

Interesting fact

Metformin is being used increasingly in treating polycystic ovarian syndrome (PCOS).

This material is not intended to substitute medical advice, but is for informational purposes only. Please consult a physician for specific treatment and recommendations.


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