Easy-to-read medicine information about metformin – what it is, how to take metformin safely and possible side effects.
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What is metformin?
- Metformin is in a class of medications called biguanides and is used to treat type 2 diabetes.
- It works by decreasing the amount of glucose you absorb from your food, decreasing the amount of glucose made by your liver, increasing your body's response to insulin (a natural substance that controls the amount of glucose in the blood) and increasing the use of sugar by your muscles.
- It can be used alone or with other medicines, including insulin, to treat diabetes.
- Metformin is also used for polycystic ovarian syndrome under specialist care as this is an unapproved indication (read more NZ Formulary)
- The usual dose for adults with diabetes starts with 500 mg (1 tablet) 1–2 times daily, increased gradually as tolerated to 1.5–2 g daily in divided doses.
- The maximum dose is usually 3 g daily in divided doses.
- Your doctor will usually start you on a low dose and increase the dose gradually, depending on your blood sugar level. This allows your body to get used to the medicine and reduces unwanted side effects.
- You may be asked to record your blood sugar levels over this time so your doctor can see how well the metformin is working.
- Always take your metformin exactly as your doctor has told you. The pharmacy label on your medicine will tell you how much metformin to take, how often to take it, and any special instructions. Ask your pharmacist if you have any questions relating to your medication.
- Treatment for diabetes is usually lifelong. Keep taking metformin everyday to control your diabetes. Speak to your doctor, nurse or pharmacist before stopping.
How to take metformin
- Always take metformin with food, during a meal or just after a snack.
- Take metformin at the same times each day.
- Do not skip meals while taking metformin.
- Limit or avoid alcohol while taking metformin. It affects the control of your blood sugar and increases your chance of getting side effects.
- If you forget to take your dose, take it (with food) as soon as you remember that day.
- But, if it is nearly time for your next dose, just take the next dose at the right time. Do not take double the dose.
- Talk to your pharmacist if you have any questions regarding your medication.
- Sometimes (very rarely) metformin may lower your blood sugar too much - called hypoglycaemia. It is likely to occur if you delay or miss a meal or snack, drink alcohol, exercise more than usual, or cannot eat because of nausea or vomiting.
- This may cause you to feel weak, faint, dizzy or irritable. You may get a headache, tremor (shakes) or blurred vision.
- If this occurs, drink something sweet such as a small glass of sweetened soft drink, or fruit juice or eat something sweet like lollies. Follow this up with a snack such as a sandwich. Tell your doctor or nurse if this happens.
- Sometimes metformin may build up in your body, and cause lactic acidosis. This is very rare. You are at highest risk if you are over 80 years of age, have kidney problems or heart failure. To avoid this, your doctor will monitor how well your kidneys are working and adjust your metformin dose accordingly. Also, your doctor may take you off metformin for a short time if you become dehydrated or experience severe diarrhoea, have a severe infection or are undergoing surgery or radiotherapy.
Possible side effectsLike all medicines, metformin can cause unwanted side effects, although not everyone gets them. Often unwanted side effects improve as your body gets used to the new medicine.
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Metformin may interact with a number of medications and herbal supplements so check with your doctor or pharmacist before starting metformin or before starting any new medicines.
Medsafe Consumer Information Sheet: metformin
New Zealand Formulary Patient Information: metformin