Disclaimer: This article is for informational purposes only and does not constitute medical advice. It is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of a physician or other qualified health provider with any questions you may have regarding a medical condition.
Overview
Metformin is a tablet that lowers blood sugar. Health Canada has authorized it for adults with type 2 diabetes, used together with diet, exercise and weight reduction.
It comes as immediate-release tablets, such as Glucophage and many generics, and as extended-release tablets, such as Glumetza. Metformin is not a treatment for type 1 diabetes.
Metformin needs a prescription. BC residents can speak with a BC-licensed doctor by phone through Avee Health to ask whether it is appropriate for them. The doctor decides based on your health history. A prescription is not guaranteed.
In Canada, metformin is authorized for adults with type 2 diabetes to:
- Improve blood sugar control, together with diet, exercise and weight reduction
Metformin is not for type 1 diabetes or diabetic ketoacidosis. Health Canada has not authorized it for children.
Metformin
Biguanide antihyperglycemic
diabetes
Prescription required
Available
How Metformin Works
Metformin belongs to a group of medicines called biguanides. It lowers blood sugar in people with type 2 diabetes. It works alongside healthy eating, physical activity and weight management, which stay part of your treatment.
Dosage Instructions of Metformin
Your doctor sets your dose. The usual doses in the Canadian product monographs are:
- Immediate-release tablets (Glucophage and generics): 500 mg three or four times a day, or 850 mg two or three times a day. The maximum is 2550 mg a day.
- Extended-release tablets (Glumetza): 1000 mg once a day with the evening meal to start. The dose may be raised by 500 mg a week. The maximum is 2000 mg once a day.
The dose starts low and is raised gradually to limit stomach upset. Older adults are kept on the lowest dose that controls their blood sugar. Your kidney function also affects whether you can take metformin and how much.
Take metformin with food. Swallow extended-release tablets whole. Do not break or crush them.
Missed dose: for immediate-release tablets, skip the missed dose and take the next one at your usual time. For Glumetza, take it as soon as you remember, unless your next dose is less than 10 hours away. Never take two doses at once.
Storage Instructions
Store at room temperature, 15°C to 30°C, in a tightly closed container. Keep out of reach of children.
Side Effects of Metformin
The most common side effects affect the stomach and gut: diarrhea, nausea, vomiting, stomach pain, bloating, gas, heartburn and loss of appetite. A metallic taste is also common when you start. Raising the dose slowly and taking metformin with food help.
In one clinical trial, these effects were reported by people taking Glumetza 2000 mg once a day and by people taking immediate-release metformin:
- Diarrhea: about 23% and 17%
- Nausea: about 15% and 14%
- Indigestion: about 13% and 8%
In clinical trials, vitamin B12 fell below the normal range in about 7% of people taking metformin.
Get medical help right away if you have:
- Signs of lactic acidosis: feeling very weak or tired, unusual muscle pain, trouble breathing, stomach pain with nausea, vomiting or diarrhea, feeling cold in your arms and legs, dizziness, or a slow or irregular heartbeat
- Severe stomach pain that does not go away, with or without vomiting, which may spread to your back (possible pancreatitis)
- Unusual tiredness, pale skin, a fast heartbeat, shortness of breath or dark urine (possible breakdown of red blood cells)
- Yellowing of your skin or eyes, pain in the upper right side of your stomach area, or unusually dark urine (possible liver problems)
- Numbness, prickling, tingling or burning pain in your hands or feet that builds up over time (possible nerve damage)
Important Safety Information About Metformin
Lactic acidosis: metformin carries a serious warning for lactic acidosis, a rare build-up of lactic acid in the blood. It is fatal in about half of cases. The risk is higher with kidney or liver problems, heavy alcohol use, dehydration, severe infection and conditions that lower oxygen in the blood. Stop metformin and get emergency care if you have the warning signs.
Do not take metformin if you have type 1 diabetes, metabolic acidosis (including diabetic ketoacidosis), a past episode of lactic acidosis, kidneys that do not work well, severe liver problems, a severe infection, a serious injury, severe dehydration or shock, or an allergy to metformin. Do not take it if you drink heavily.
Kidneys: metformin leaves the body through the kidneys. Your doctor checks your kidney function with a blood test before you start and regularly after that. Metformin is not used when the kidneys work poorly.
Age over 80: metformin is not started unless a test shows that kidney function is not reduced.
X-rays or scans with iodine contrast dye: metformin is stopped before the test and not taken for 48 hours after it. It is restarted only once your kidney function has been rechecked and is normal. Ask your care team when to stop.
Surgery: metformin is stopped 2 days before surgery. It is restarted once you are eating and drinking again and your kidney function is normal.
Vitamin B12: long-term use can lower vitamin B12, which can cause pins and needles in your hands and feet. A blood test is advised at least every 1 to 2 years.
Low blood sugar: this is more likely if you also take other medicines that lower blood sugar, do not eat enough, drink alcohol, exercise heavily without eating enough, or are older.
Pregnancy and breastfeeding: do not take metformin if you are pregnant, planning a pregnancy or breastfeeding. Very small amounts pass into breast milk. Talk to your doctor about how to manage your diabetes.
Drug Interactions
Tell your doctor and pharmacist about everything you take, including non-prescription products. The main interactions are:
- Alcohol: it adds to the effect of metformin on lactic acid. Avoid heavy drinking, whether in one sitting or regularly.
- Glyburide and other medicines that lower blood sugar: the risk of low blood sugar is higher.
- Furosemide and nifedipine: these can change the level of metformin in your blood.
- Medicines removed by the kidneys in the same way as metformin, such as cimetidine, ranitidine, digoxin, morphine, quinidine, quinine, procainamide, amiloride, triamterene, trimethoprim and vancomycin.
- Medicines that can raise blood sugar, such as thiazide water pills, corticosteroids, estrogens and birth control pills, phenytoin, nicotinic acid, isoniazid, phenothiazines, calcium channel blockers and some asthma and decongestant medicines.
- Levothyroxine, ACE inhibitors and blood thinners that block vitamin K: your doctor may monitor you more closely.
Brands & DIN Number of Metformin
Brand Names
- Glucophage
- Glumetza
Key Takeaways
- 1Metformin is a tablet authorized in Canada for adults with type 2 diabetes, used along with diet and exercise.
- 2It comes as immediate-release tablets (Glucophage and generics) and extended-release tablets (Glumetza).
- 3The dose starts low and is raised gradually. The maximum is 2550 mg a day for immediate-release tablets and 2000 mg a day for Glumetza.
- 4Diarrhea, nausea and stomach upset are the most common side effects. Taking metformin with food helps.
- 5Lactic acidosis is rare but serious. Kidney function is checked, and metformin is paused around contrast dye tests and surgery.
- 6Long-term use can lower vitamin B12, so a blood test is advised at least every 1 to 2 years.
- 7Metformin needs a prescription. BC residents can ask a BC-licensed doctor by phone whether it is right for them.
Frequently Asked Questions
How much does metformin cost in Canada, and does BC PharmaCare cover it?
How do I get metformin in BC?
What is the difference between immediate-release and extended-release metformin?
Is generic metformin the same as Glucophage?
Can I drink alcohol while taking metformin?
Why do I have to stop metformin before a scan with contrast dye or surgery?
Does metformin cause vitamin B12 deficiency?
Can I take metformin during pregnancy or breastfeeding?
Avee Editorial
Avee Editorial Team