Metformin is the usual first medicine for type 2 diabetes. It does not cause low blood sugar on its own, which sets it apart from several other diabetes treatments — but it does upset a lot of stomachs in the first few weeks, and that is very manageable if you know what to expect.
Type 2 diabetes, where it reduces the amount of glucose the liver releases and helps the body respond better to its own insulin. It is also used in polycystic ovary syndrome, and sometimes in prediabetes.
On its own it very rarely causes hypoglycaemia. Combined with insulin or certain other diabetes medicines, hypos become possible.
Take it with or just after a meal — this makes a real difference to stomach side effects. Doses are usually built up gradually for the same reason.
Modified-release tablets are swallowed whole and never crushed or chewed. You may see the empty shell in your stool; that is normal and does not mean it has not worked.
If stomach upset is a problem despite taking it with food, ask about the modified-release version — many people tolerate it much better.
Nausea, diarrhoea, stomach ache, loss of appetite and a metallic taste are common in the first few weeks and usually settle.
Long-term use can lower vitamin B12 levels, so this is checked periodically. Tell your GP about persistent tiredness, pins and needles, or numbness.
Stop metformin temporarily if you become dehydrated — vomiting, diarrhoea, or fever with heavy sweating — and restart when you have been eating and drinking normally for 24 to 48 hours. The same applies before certain scans using contrast dye, and around some operations.
Ask us or your diabetes team for a sick day rules card if you do not already have one. It lists everything you should pause and when.
Alcohol in excess increases the risk of lactic acidosis and can cause blood sugar swings — keep within recommended limits and avoid binge drinking.
Tell your prescriber about diuretics, steroids and blood pressure medicines, all of which can affect kidney function or blood sugar.
Metformin can be used in pregnancy where appropriate — discuss with your diabetes team rather than stopping on your own.
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