Side Effects Of Metformin

NHS medicines information on side effects of metformin and what you can do to cope.

Like all medicines, metformin can cause side effects, although not everyone gets them.

Common side effects

These common side effects of metformin happen in more than 1 in 100 people. There are things you can do to help cope with them:

If this advice does not help and any of these side effects continue to bother you, tell your doctor or pharmacist.

Vitamin B12 deficiency

Taking metformin can cause vitamin B12 deficiency. Call your doctor or call 111 straight away if you:

• feel very tired
• have muscle weakness
• have a sore, red tongue
• have mouth ulcers
• have problems with your vision
• have pale or yellow skin (this may be less obvious on brown or black skin

Your doctor can check your vitamin B12 serum levels. If they are too low, they may prescribe B12 vitamin supplements.

Low blood sugar

Metformin does not usually cause low blood sugar (known as hypoglycaemia, or "hypos") when taken on its own. But hypos can happen when you take metformin with other diabetes medicines, such as insulin or gliclazide.

Early warning signs of low blood sugar include:

• feeling hungry
• trembling or shaking
• sweating
• confusion
• difficulty concentrating

It's also possible for your blood sugar to go too low while you're asleep. If this happens, it can make you feel sweaty, tired and confused when you wake up.

Low blood sugar may happen if you:

• take too much of some types of diabetes medicines
• do not eat meals at regular times or skip meals
• are fasting
• do not eat a healthy diet and are not getting enough nutrients
• change what you eat
• exercise too much without eating enough carbohydrates
• drink alcohol, especially after skipping a meal
• take some other medicines or herbal remedies at the same time
• have a hormone disorder, such as an underactive thyroid (hypothyroidism)
• have kidney or liver problems

To prevent hypoglycaemia, it's important to have regular meals, including breakfast. Try not to miss or delay a meal.

If you're planning to exercise more than usual, make sure you eat carbohydrates like bread, pasta or cereals before, during or after exercise.

Always carry a fast-acting carbohydrate with you, like sugar cubes, fruit juice or some sweets, in case your blood sugar level gets low. Artificial sweeteners will not help.

You may also need to eat a starchy carbohydrate, like a sandwich or a biscuit, to maintain your blood sugar for longer.

Call your doctor or call 111 if taking in sugar does not help, or the hypo symptoms come back

Make sure your friends and family know about your diabetes and the symptoms of low blood sugar levels so they can recognise a hypo if it happens.

Serious side effects

Serious side effects are rare and happen in less than 1 in 10,000 people.

Call your doctor or call 111 straight away if:

• you get a general feeling of being unwell with severe tiredness, fast or shallow breathing, being cold and a slow heartbeat
• the whites of your eyes turn yellow, or your skin turns yellow, although this may be less obvious on brown or black skin - this can be a sign of liver problems

Serious allergic reaction

In rare cases, it's possible to have a serious allergic reaction (anaphylaxis) to metformin.

Long-term side effects

Taking metformin can cause vitamin B12 deficiency if you take it for a long time. This can make you feel very tired, breathless and faint, so your doctor may check the vitamin B12 level in your blood.

If your vitamin B12 levels become too low, vitamin B12 supplements will help.

Other side effects

These are not all the side effects of metformin. For a full list, see the leaflet inside your medicine packet.

If you want to find out more about this particular topic you can visit the Original article on the NHS website. If you are worried by any aspect of your health make sure you go and see your doctor or book an appointment at your local clinic.