Metformin at a glance
Medicine class
Biguanide blood-glucose-lowering medicine.
Available forms
Immediate-release and prolonged-release tablets, oral liquids and powder dissolved in water.
With food
Taking metformin with or just after food can reduce digestive side effects.
Low blood sugar
Metformin alone does not usually cause hypoglycaemia, but risk increases with insulin or certain other diabetes medicines.
What is Metformin used for?
Selected UK products are licensed for:
Type 2 diabetes when diet and physical activity do not adequately control blood glucose. Selected immediate-release tablets, liquids and powder are licensed for adults and children aged 10 years and over; the selected prolonged-release product is for adults.
Use alone or with other appropriate diabetes medicines. Selected immediate-release products permit paediatric use alone or with insulin.
The selected Xynox prolonged-release range is also licensed to reduce or delay type 2 diabetes in specified overweight adults at high risk whose glucose measures worsen despite intensive lifestyle change.
Metformin is sometimes prescribed outside its licence for polycystic ovary syndrome to improve insulin handling, ovulation or menstrual regularity.
How does Metformin work?
Metformin reduces glucose production by the liver, improves the body's response to insulin and increases glucose uptake by tissues. It also reduces some glucose absorption from the gut without directly stimulating insulin secretion.
Metformin preparations and strengths
Modified-release tablet
Route: Oral
Strengths: 500 mg, 750 mg, 850 mg, 1000 mg
Oral solution
Route: Oral
Strengths: 500 mg, 500 mg/5 mL, 850 mg/5 mL, 1000 mg/5 mL
How to take Metformin
Follow the label and instructions for the supplied formulation.
Take with or just after food to improve stomach tolerability.
Swallow tablets with water. Prolonged-release tablets must be swallowed whole, not chewed.
Measure oral liquid with the supplied measuring device, not a household teaspoon.
Dissolve powder sachets in water as directed and drink immediately.
Some oral liquids can be given through suitable enteral feeding tubes; follow the product's flushing instructions.
Metformin side effects
Common or expected effects
- Nausea or vomiting
- Diarrhoea
- Abdominal discomfort
- Reduced appetite
- Altered or metallic taste
- Reduced vitamin B12 levels, particularly with longer use or other risk factors
Get urgent medical advice
- Possible lactic acidosis: rapid or difficult breathing, severe weakness, muscle cramps, abdominal pain, feeling cold or marked drowsiness
- Severe allergic reaction with facial, mouth or throat swelling or breathing difficulty
- Yellow skin or eyes, dark urine or other possible signs of liver inflammation
Metformin in pregnancy
Metformin can be used to treat diabetes during pregnancy when clinically appropriate. Good glucose control is important before conception and throughout pregnancy, so treatment should be reviewed with the diabetes or maternity team rather than stopped without advice.
Metformin while breastfeeding
UK specialist advice considers metformin a preferred option for mothers of full-term, healthy infants because negligible amounts enter milk. Product information is more cautious because infant data are limited; individual assessment is appropriate, particularly for premature or unwell babies.
Metformin interactions
Tell the prescriber, pharmacist and imaging or surgical team that metformin is being taken. Important examples include:
Iodinated contrast media
Contrast used for some scans can impair kidney function and increase metformin accumulation; the clinical team may temporarily interrupt treatment and reassess renal function.
Alcohol
Heavy or acute alcohol intake increases lactic acidosis risk, especially with fasting, malnutrition or liver impairment.
NSAIDs, ACE inhibitors, angiotensin-II receptor blockers and diuretics
These can worsen kidney function in susceptible people, increasing the need for renal monitoring.
Common questions about Metformin
Answers are fully visible for fast scanning and source review.
Does metformin hydrochloride cause low blood sugar?
Not usually when taken alone. It can occur when combined with insulin, sulfonylureas or meglitinides.
Does metformin hydrochloride cause weight gain?
Metformin is not usually associated with weight gain.
Can prolonged-release tablets be crushed or chewed?
No. Swallow them whole to maintain their prolonged-release properties.
What should someone do during severe vomiting or diarrhoea?
Dehydration can increase metformin accumulation and lactic acidosis risk. Temporarily stop it and contact a healthcare professional.
Sources
These sources were used to prepare and review this medicine page.
Prepared and reviewed by the iatroX editorial team.