Medicine guide · Diabetes
Metformin
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Metformin is a common, low-cost pill for type 2 diabetes. It helps keep your blood sugar in a healthy range and is often the first diabetes medicine a doctor prescribes.
| Brand names | Glucophage, Glumetza |
| Type of medicine | Biguanide (diabetes medicine) |
| Available as | Tablets, regular and extended-release |
| Prescription | Yes, prescription only |
Reviewed by a pharmacist · Last reviewed November 15, 2026
- What it’s for
- How it works
- How to take it
- If you miss a dose
- Side effects
- Interactions and cautions
- Storage
- Pharmacist tips
- Common questions
- Related medicines
- Sources
What it’s for
Metformin is used to treat type 2 diabetes in adults and some children. It works best together with healthy eating and regular physical activity.
It can be taken alone or with other diabetes medicines, including insulin. Your doctor may also prescribe it for other conditions, such as polycystic ovary syndrome (PCOS).
How it works
When you have type 2 diabetes, your body has trouble using sugar from food for energy, so sugar builds up in your blood. Metformin helps in two main ways:
- It tells your liver to make less sugar.
- It helps your body respond better to insulin, the hormone that moves sugar out of your blood and into your cells.
On its own, metformin rarely causes low blood sugar.
How to take it
- Take it with meals. This helps prevent an upset stomach.
- Your doctor will usually start with a low dose and raise it slowly over a few weeks. This gives your stomach time to adjust.
- Extended-release tablets (such as Glumetza) are usually taken once a day with the evening meal. Swallow them whole. Do not crush, cut or chew them.
- Keep taking metformin even if you feel well. Diabetes often has no symptoms, but high blood sugar can still harm your body over time.
If you miss a dose
Take the missed dose with your next meal if you remember soon. If it is almost time for your next dose, skip the missed dose and go back to your usual schedule.
Do not take two doses at once to make up for a missed one.
Side effects
Common side effects
These are usually mild and often get better within a few weeks:
- Diarrhea
- Nausea or upset stomach
- Gas or bloating
- A metallic taste in your mouth
- Less appetite
Taking metformin with food, and raising the dose slowly, helps. If stomach problems don’t go away, talk to your doctor or pharmacist. An extended-release tablet may be easier on your stomach.
Over the long term
Using metformin for many years can lower your vitamin B12 level. Ask your doctor whether you should have your B12 checked from time to time, especially if you notice numbness or tingling in your hands or feet.
Get emergency help right away if you have:
- Unusual muscle pain or weakness
- Trouble breathing
- Unusual sleepiness, or feeling very tired or weak
- Stomach pain with nausea or vomiting
- Feeling very cold, dizzy or light-headed
- A slow or uneven heartbeat
These can be signs of lactic acidosis, a very rare but serious side effect. It is more likely if you have kidney problems, drink a lot of alcohol, or are very sick and dehydrated.
Interactions and cautions
Tell your doctor and pharmacist about all the medicines, vitamins and natural products you take. Be especially careful with:
- Alcohol. Drinking a lot, or binge drinking, raises the risk of lactic acidosis.
- Other diabetes medicines, such as insulin or glyburide. Together with metformin, these can cause low blood sugar.
- Steroids such as prednisone. They can raise your blood sugar.
You may need to stop metformin for a short time:
- Before a scan with contrast dye (some CT scans and X-rays). Tell the staff that you take metformin.
- Before surgery. Your care team will tell you when to stop and restart.
- When you are sick and can’t keep fluids down, for example with vomiting, diarrhea or a fever. Ask your pharmacist for a “sick day plan” so you know what to do.
Storage
- Store at room temperature, away from heat and moisture. A bathroom cabinet is not a good place.
- Keep it in its original container, out of sight and reach of children.
- Return unused or expired tablets to your pharmacy for safe disposal.
Pharmacist tips
From your pharmacist
- If you take extended-release metformin, you might see what looks like a tablet in your stool. This is normal. It’s the empty shell, and the medicine has already been absorbed.
- Metformin is also found in combination pills with other diabetes medicines, such as Janumet, Xigduo and Synjardy. Check your labels so you don’t take it twice.
- Keep a list of your medicines, and bring it to every appointment.
Common questions
Does metformin cause weight gain?
No. Metformin doesn’t usually cause weight gain, and some people lose a small amount of weight while taking it.
When is the best time to take metformin?
Take it with meals to help prevent an upset stomach. Extended-release tablets are usually taken once a day with the evening meal.
Can I drink alcohol while taking metformin?
A small amount of alcohol with food is usually okay for most people. Heavy drinking or binge drinking raises the risk of lactic acidosis and low blood sugar, so avoid it.
Can metformin cause low blood sugar?
Rarely, when taken on its own. The risk is higher if you also take insulin or certain other diabetes pills, skip meals or drink alcohol.
Will I have to take metformin forever?
Type 2 diabetes is usually a long-term condition, so many people take metformin for years. Your doctor may change the dose over time. Don’t stop taking it without talking to your doctor.
Related medicines
Other medicines used for the same condition:
Sources
- Health Canada. Drug Product Database: product monographs for metformin hydrochloride (Glucophage, Glumetza).
- Diabetes Canada. Clinical Practice Guidelines, including sick-day medication guidance.
- U.S. National Library of Medicine. MedlinePlus: Metformin.
This page gives general information only and does not replace advice from your doctor, nurse practitioner or pharmacist. Do not start, stop or change a medicine without talking to your health care team. In an emergency, call 911.