I am on metformin. Is it safe? How can I prevent side effects?

Metformin tablets

Metformin tablet is often prescribed as the first medication for the treatment of type 2 diabetes along with healthy lifestyle advice. Doctors have been prescribing Metformin for more than 60 years to reduce blood sugar in people with type 2 diabetes. A French physician, called  Jean Sterne, first reported the use of metformin to treat diabetes in 1957. Doctors have huge experience with this medication.

The main advantages of metformin are that hypoglycaemia (a low blood sugar) is uncommon and unlike sulphonylureas (gliclazide, glimepiride),it  is less likely to cause weight gain.  Metformin can also be taken in addition to other glucose lowering tablets and insulin, if the blood glucose is not controlled.

Metformin is also prescribed for Polycystic ovary syndrome (PCOS) by some endocrinologists.


How does metformin work?

Metformin works in a number of ways in people with type 2 diabetes.

  • It lowers blood glucose (sugar) mainly by decreasing the amount of glucose that your liver releases into the blood stream.
  • It increases the sensitivity of your body’s cells to insulin (so more glucose is taken into cells with the same amount of insulin in the blood stream). That is it lowers insulin resistance.
  • It delays the uptake of sugar from the intestines into the blood stream after eating.

There are several other actions of metformin.

In addition metformin is also prescribed for people with Type 1 diabetes with obesity. as it lowers insulin resistance.

How do I take metformin?

Your diabetes consultant will tell you when and how to take your tablets.  It is recommended to  gradually increase your metformin dose thereby reducing the chance of side effects.

You may try this regime, when you are starting metformin:

First week:  Take one tablet each day after the largest meal of the day.

Second week: Take one tablet after breakfast and one tablet after your evening meal.

Thereafter increase metformin to a maximum recommended dose of 2000mg per day, divided into two or three times a day. Swallow the tablet with water and do not chew. Always take metformin during or after a meal.


What are the side effects?

Metformin is well tolerated  and widely prescribed tablet. However there are some side effects of metformin, which are mentioned below:

  • Nausea/vomiting
  • Loss of appetite
  • Increased flatulence
  • Diarrhoea
  • Weight loss
  • Rash/Itching
  • Abdominal pain
  • Metallic taste
  • B12 deficiency
  • Lactic acidosis

These side effects can usually be avoided by taking metformin after food. Mild nausea and stomach upset usually disappear after a few weeks. If you continue to suffer from these side effects, you may be switched to a metformin preparation called Glucophage SR which has a lower rate of abdominal side effects. However if you still have side effects with slow release metformin, this medication has to be discontinued and another class of medication tried for type 2 diabetes.

People taking metformin can have reduced absorption of B12 and can have B12 deficiency.

Lactic acidosis is a rare side effects seen in people with heart failure and renal failure.

Please see leaflet inside the drug packet for more details.

Contradictions : When should I not take metformin?

Below are some of conditions when metformin should be stopped:

  • Severe dehydration
  • Moderate to severe kidney failure
  • Severe Heart failure
  • Recent Heart attack
  • planning for a scan with contrast
  • Liver failure
  • Alcoholism

What is Slow Release (SR) Metformin?

Slow release metformin like Glucophage SR tablets are designed to release metformin slowly and continuously over several hours. This produces a steady blood level of the medicine throughout the day. The tablets are designed to be taken once or twice a day with meals, depending on the advice of your diabetes consultant.  They must be swallowed with water and not broken down, chewed or crushed, as this would damage the slow release action. It is common to notice the outer layer of metformin slow release tablet to pass through your gut undigested and be visible in your faeces. People who have had gastric bypass surgery should avoid slow release metformin.

What to do if I forget a dose?

As soon as you remember, take the prescribed dose with your next meal.  Then go on as prescribed. Never double the dose.

How long does it take to work?

This usually varies. It may take a few days to two weeks to get maximum reduction of blood sugars.  If there is very little or no reduction of blood sugar levels after 2 weeks, your diabetes consultant may increase the dose. To get the maximum benefit from any of these tablets you should continue to improve your lifestyle by eating a healthy balanced diet and taking part in physical activity.

Are there any tablets I should not take?


Some tablets may affect the way these tablets work or affect your diabetes control. Please check with your diabetes consultant or pharmacist. It is important tell your doctor or nurse that you are metformin, when you are to be prescribed new medications, going for surgery or having any scans.

How to store metformin

Always store metformin in a cool dry place, away from direct heat and light.

Where can I get more information?

Your consultant diabetologist will be able to provide you more detailed information and advice about the metformin.  Information is also available from the leaflet inside the metformin box.

Dr Chinnadorai Rajeswaran is a consultant Physician specialising in Endocrinology, Diabetes and Obesity. As a private endocrinologist he  has private endocrine, diabetes and weight loss clinics in Harley Street, London, Chennai (India), Claremont Hospital, Sheffield, Nuffield Hospital, Leeds and Simplyweight, Bradford.

He has face to face consultations with people from Barnsley, Rotherham, Chesterfield, Doncaster, Wakefield, Huddersfield, Bradford, Harrogate, Leeds, Sheffield, London and Chennai (India). He also offers video consultations.

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