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Metformin (Metformin 500mg tablets)



Information specific to: Metformin 500mg tablets when used in Diabetes.

Metformin (met-form-in hi-droh-clor-ride) is a medicine which is used in diabetes mellitus.

The information in this Medicine Guide for metformin varies according to the condition being treated and the particular preparation used.

Your medicine

Diabetes leads to problems controlling blood sugar levels. Metformin hydrochloride has many effects on the body and can help certain people with diabetes to keep their blood sugar level under control.

It is very important that your blood sugar level is well controlled. Blood sugar levels which are too high or too low can be dangerous. Your prescriber or a member of your diabetes team will be able to give you information on how to recognise the warning signs of high and low blood sugar levels. They will also be able to tell you what to do if either of these occurs.

Warning signs can vary from person to person. If the usual warning signs of poorly controlled blood sugar levels change or disappear, you should contact your prescriber or a member of your diabetes team.

The amount of Metformin hydrochloride you need to control your blood sugar levels will be worked out by your prescriber or your diabetes team. They may also advise you to measure your blood sugar regularly – they will show you how to do this. If you are having problems controlling or measuring your blood sugar, you should contact your prescriber or a member of your diabetes team.

Do not share your medicine with other people. It may not be suitable for them and may harm them.

The pharmacy label on your medicine tells you how much medicine you should take. It also tells you how often you should take your medicine. This is the dose that you and your prescriber have agreed you should take. You should not change the dose of your medicine unless you are told to do so by your prescriber.

If you feel that the medicine is making you unwell or you do not think it is working, then talk to your prescriber.

Whether this medicine is suitable for you

Metformin hydrochloride is not suitable for everyone and some people should never use it. Other people should only use it with special care. It is important that the person prescribing this medicine knows your full medical history.

Your prescriber may only prescribe this medicine with special care or may not prescribe it at all if you:

  • are about to have a procedure under general anaesthesia
  • are allergic or sensitive to or have had a reaction to any of the ingredients in the medicine
  • are an alcoholic or are currently intoxicated with alcohol
  • are elderly
  • are in shock
  • have a condition which may alter your kidney function such as dehydration or an infection
  • have a condition which may cause a low level of oxygen in the blood such as breathing problems
  • have ketoacidosis or are at risk of going into a coma
  • have kidney problems
  • have liver problems
  • have or have had certain heart problems
  • have risk factors for lactic acidosis such as diabetes which is uncontrolled, ketosis, prolonged fasting or drinking alcohol heavily

Furthermore the prescriber may only prescribe this medicine with special care or may not prescribe it at all for a child who is under 10 years of age.

As part of the process of assessing suitability to take this medicine a prescriber may also arrange tests:

  • to determine whether or not the medicine is suitable and whether it must be prescribed with extra care
  • to confirm that this is the right dose
  • to check that this medicine is not having any undesired effects

Over time it is possible that Metformin hydrochloride can become unsuitable for some people, or they may become unsuitable for it. If at any time it appears that Metformin hydrochloride has become unsuitable, it is important that the prescriber is contacted immediately.


Alcohol can interact with certain medicines.

In the case of Metformin hydrochloride:

  • this medicine interacts with alcohol

You must not drink any alcohol if you are taking this medicine.


Medicines can interact with certain foods. In some cases, this may be harmful and your prescriber may advise you to avoid certain foods.

In the case of Metformin hydrochloride:

  • Metformin hydrochloride is not known to interact with food. You should continue on the diet advised by your dietician or prescriber

For more advice speak to your prescriber, dietitian or pharmacist.

Driving and operating machinery

When taking any medicine you should be aware that it might interfere with your ability to drive or operate machinery safely.

In the case of Metformin hydrochloride:

  • this medicine will not affect your ability to drive or operate machinery

You should see how this medicine affects you before you judge whether you are safe to drive or operate machinery. If you are in any doubt about whether you should drive or operate machinery, talk to your prescriber.

Family planning and pregnancy

Most medicines, in some way, can affect the development of a baby in the womb. The effect on the baby differs between medicines and also depends on the stage of pregnancy that you have reached when you take the medicine.

In the case of Metformin hydrochloride:

  • if you become pregnant, or think you have become pregnant while taking Metformin hydrochloride, you must contact your prescriber

People with diabetes may start to have insulin instead of Metformin hydrochloride to control their blood sugar during pregnancy. If you are taking Metformin hydrochloride and are planning to become pregnant, become pregnant or think that you are pregnant, talk to a member of your diabetes team. For more information on managing your diet and your diabetes during your pregnancy, talk to your prescriber or a member of your diabetes or antenatal team.


Certain medicines can pass into breast milk and may reach your baby through breast-feeding.

In the case of Metformin hydrochloride:

  • this medicine passes into breast milk

Women who are taking Metformin hydrochloride must not breast-feed. If you wish to breast-feed you should discuss with your prescriber whether there are any other medicines you could have. You should not stop this medicine without taking advice from your doctor.

Taking other medicines

If you are taking more than one medicine they may interact with each other. At times your prescriber may decide to use medicines that interact, in other cases this may not be appropriate.

The decision to use medicines that interact depends on your specific circumstances. Your prescriber may decide to use medicines that interact, if it is believed that the benefits of taking the medicines together outweigh the risks. In such cases, it may be necessary to alter your dose or monitor you more closely.

Tell your prescriber the names of all the medicines that you are taking so that they can consider all possible interactions. This includes all the medicines which have been prescribed by your GP, hospital doctor, dentist, nurse, health visitor, midwife or pharmacist. You must also tell your prescriber about medicines which you have bought over the counter without prescriptions.

The following medicines may interact with Metformin hydrochloride:

  • insulin

The following types of medicine may interact with Metformin hydrochloride:

  • antihypertensives
  • diuretics
  • glucocorticosteroids
  • iodinated contrast media
  • loop diuretics
  • meglitinides
  • non-steroidal anti-inflammatories
  • other oral antidiabetics
  • sulphonylureas
  • sympathomimetics

If you are taking Metformin hydrochloride and one of the above medicines or types of medicines, make sure your prescriber knows about it.

Complementary preparations and vitamins

Medicines can interact with complementary preparations and vitamins.

Make sure you tell your prescriber the names of all the complementary preparations and vitamins that you are taking or are planning to take.

Your prescriber can then decide whether it is appropriate for you to take combinations that are known to interact.

In the case of Metformin hydrochloride:

  • this medicine may interact with vitamin B12

If you have been prescribed Metformin hydrochloride you should only take something on the above list on the specific advice of your prescriber or pharmacist.

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