Open a PDF version to print this topic

HealthInfo Canterbury

Metformin treatment

FDP badmintonMetformin helps our body use insulin and may help us lose weight. It's often used to treat people with diabetes mellitus (sugar diabetes).

Metformin also helps to restore normal periods in about half of women with polycystic ovary syndrome (PCOS). As well, it can lower the levels of male-type hormones (androgens) and may improve unwanted facial hair.

In people with prediabetes or impaired glucose tolerance, metformin reduces the risk of developing diabetes by a third. But a sensible diet and walking for 30 minutes a day is even more effective, reducing the risk by two-thirds.

Metformin isn't a contraceptive and may even help you ovulate. If you don't want to become pregnant, you need to use contraception.

The most common side effects of metformin are tummy upsets such as nausea (feeling sick), diarrhoea (the runs) and indigestion. These are much more common if you take metformin on an empty stomach, so it's best to take it with or after meals. If you have loose bowel motions that aren't too bad, or mild indigestion, they'll probably get better with time and you won't have to stop the metformin.

Side effects are much less of a problem if you start with a low dose and build it up. Your doctor will probably discuss this with you.

If you get side effects after you've increased the dose, go back to the dose that was OK. Don't stop it altogether.


Stop taking metformin if you're very sick. Make sure you tell any doctor who's treating you when you're sick that you've been on metformin. This is especially so if you have:

If you're having major surgery, stop the metformin before surgery and while you're recovering in hospital. If you want to get pregnant, you should talk to your doctor about whether you should keep taking it.

In summary, if you have PCOS, metformin may make your periods more regular and may help with weight loss. But diet and exercise are still the best ways to lose weight and prevent diabetes. Metformin is a safe medicine to take but remember to stop it if you get unwell.

See also:



Written by the Department of Endocrinology, Christchurch Hospital. Adapted by HealthInfo clinical advisers. Last reviewed April 2018.

Image courtesy of anankkml at

Page reference: 70668

Review key: HIMET-70668