Metformin
The first-choice tablet for type 2 diabetes for decades. Cheap, well proven, and doesn’t cause hypos or weight gain on its own. Your gut may need a few weeks to warm to it.
At a glance
- For
- Type 2 diabetes. Also used for prediabetes, polycystic ovary syndrome (PCOS) and diabetes in pregnancy
- Works
- Lowers HbA1c by about 1% on its own. In the UKPDS trial in overweight people, it cut deaths by about a third over 10 years. In prediabetes, it cuts the chance of diabetes by about a third (lifestyle change does even better)
- Cost
- Under the $25 PBS co-payment, about $22–23 a script for generics (brand premium extra); $7.70 concession. 60-day scripts available
- Kicks in
- Sugars start falling within days; near full effect in about 2 weeks; HbA1c shows it by 3 months
- Taken for
- Usually long term
- Watch for
- Nausea, diarrhoea, tummy pain, less appetite, metallic taste
Take it with meals, start low and build up. Slow-release (XR) is kinder to the gut. Swallowing a full dose on an empty stomach is a bold move your bowels will remember.
Brand names
- Diabex, Diaformin, plus generic brands sold as metformin
- Slow-release: Diabex XR, Diaformin XR, Metex XR and generic XR brands
- In combination tablets: Janumet, Jardiance Duo, Xigduo XR, Galvumet and others
How it works
Mainly makes the liver release less glucose, and helps the body respond better to its own insulin. It doesn’t make the pancreas pump out more insulin, so on its own it rarely causes hypos.
Used for
- Type 2 diabetes, alone or with other diabetes medicines, including insulin (TGA-approved)
- Prediabetes and polycystic ovary syndrome (off-label)
- Diabetes in pregnancy, under specialist care
Side effects
Full side-effect list (from the product information)
How often, from the official product information. Bold = serious.
Very common more than 1 in 10
- Nausea, vomiting
- Diarrhoea
- Tummy pain
- Less appetite
Common 1 in 10 to 1 in 100
- Taste changes (often metallic)
- Low vitamin B12 with long-term use
Very rare fewer than 1 in 10,000
- Lactic acidosis
- Abnormal liver tests or hepatitis
- Skin reactions: redness, itch, hives
Get help urgently if
- Feeling very unwell with fast breathing, muscle pain or cramps, tummy pain, vomiting, drowsiness or feeling cold (possible lactic acidosis, rare)
- Vomiting or diarrhoea so bad you can’t keep fluids down: pause metformin and see a doctor the same day
Good to know
- Sick days: if you’re vomiting, have diarrhoea or can’t drink properly, pause metformin until you’re eating and drinking normally again.
- Kidneys: the dose is lowered if kidney function drops, and it’s stopped if kidney function is very low. Kidney blood tests at least once a year.
- Scans and surgery: tell the team you take it. It may be paused around operations and X-ray dye (contrast) if your kidneys aren’t at full strength. Heavy drinking raises the risk of lactic acidosis.
- Vitamin B12 can drop over years. Tingling or numb feet aren’t always the diabetes, so B12 is worth checking. See B12 deficiency.
Common questions
Does metformin cause weight loss?
It’s weight-neutral or leads to a small loss of a couple of kilos. Helpful, but it isn’t a weight-loss medicine.
How do I stop metformin upsetting my stomach?
Take it with meals, start on a low dose and increase slowly, or ask about the slow-release (XR) version. Gut side effects usually settle within a few weeks.
Does metformin cause vitamin B12 deficiency?
It can, with long-term use. Low B12 is listed as common (between 1 in 10 and 1 in 100 people), so periodic B12 checks make sense, especially if you get tingling or numb feet.
Should I stop metformin when I’m sick?
If you’re vomiting, have diarrhoea or are dehydrated, pause it until you’re eating and drinking normally, and follow your sick-day plan. Restart once you’re well.
Information only. Not a recommendation or endorsement of any product. Whether a medicine suits you depends on your health and other medicines, so talk to your doctor or pharmacist. In an emergency, call 000 (Australia) or your local emergency number. From a mobile, 112 works in most countries.
More information
- UKPDS 34: Metformin in overweight people with type 2 diabetes (The Lancet, 1998)
- Diabetes Prevention Program: Lifestyle or metformin for prediabetes (NEJM, 2002)
- PBS: Metformin items and prices
- NPS MedicineWise: Medicine Finder
maladywise.com/medicines/metformin/