Biguanide antidiabeticPrescription required in Canada

Metforminmetformin hydrochloride

Also sold as: Glucophage, Glumetza (extended-release), Glycon, Riomet (liquid)

The usual first medication for type 2 diabetes in Canada — inexpensive, well studied, and taken with meals.

Quick answer

What it is: A biguanide — it mainly reduces the amount of glucose the liver releases, and improves how well the body responds to its own insulin.
What it's used for: First-line treatment of type 2 diabetes, alone or with other diabetes medications. Also used off-label in PCOS and prediabetes.
Worth knowing: Always take it with or straight after food, and expect the dose to be increased gradually. Extended-release causes far less stomach upset.
Main safety point: Hold it before a CT scan with contrast dye, and during serious illness, vomiting or dehydration. On its own it does not cause low blood sugar.

Already taking Metformin? Pill4Me pharmacists in Chilliwack can help.

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Drug class

Biguanide antidiabetic

Use in Canada

Highest-volume generic antidiabetic — approximately 12,000,000 dispensings annually

DIN (Canada)

02229949, 02229950 +1 more

What is Metformin?

Metformin is the first-line medication for managing type 2 diabetes in adults. It is used alone or in combination with other diabetes medications (including insulin) to lower blood sugar. It is particularly recommended for people with type 2 diabetes who are overweight or obese. It may also be used off-label for polycystic ovary syndrome (PCOS) and prediabetes prevention.

How Metformin works

Metformin works in several ways: it reduces the amount of glucose your liver releases into the blood (the main effect), it improves your body's sensitivity to insulin so cells can use glucose more effectively, and it slightly slows how quickly the gut absorbs glucose from food. Unlike some diabetes medications, metformin does not cause weight gain and does not cause low blood sugar (hypoglycemia) when used alone.

Forms and strengths

Immediate-release tablets: 500 mg and 850 mg (taken 2–3 times daily with meals). Extended-release tablets (Glumetza, Metformin ER): 500 mg and 1000 mg (taken once or twice daily with dinner). Oral liquid (Riomet): 500 mg/5 mL for patients who cannot swallow tablets. Generic metformin is available in all forms at minimal cost.

How Metformin is taken

Always take with or immediately after a meal to reduce stomach upset. Start low (500 mg once or twice daily) and increase gradually over several weeks to minimize GI side effects. Maximum daily dose is 2550 mg (immediate release) or 2000 mg (extended release). Extended-release tablets cause significantly less nausea and diarrhea in most patients.

This is general information, not a dose for you. Dosing depends on the reason you are taking it, your kidney and liver function, your age, and everything else you take — follow the directions on your own label, and ask us if they differ from what you read here.

If you miss a dose

Take the missed dose with your next meal if you remember reasonably soon. If your next scheduled dose is close, skip the one you missed — do not double up, as that mainly produces stomach upset. Missing an occasional dose does not undo your blood sugar control.

Side effects

Common — usually manageable

Nausea — most common, especially when starting or increasing dose
Diarrhea or loose stools
Stomach cramping, bloating, or discomfort
Metallic taste in the mouth
Decreased appetite (can be a useful side effect in overweight patients)
Side effects are much less common with extended-release formulations and usually improve after 2–4 weeks

Get medical help for these

Lactic acidosis (rare but potentially fatal) — buildup of lactic acid in the blood; symptoms: severe nausea/vomiting, stomach pain, weakness, difficulty breathing, muscle pain or cramping, feeling cold, dizziness, slow or irregular heartbeat — go to emergency immediately
Vitamin B12 deficiency — occurs in 10–30% of long-term users; may cause numbness, tingling, fatigue, or cognitive changes; your doctor should check B12 levels every 2–3 years
Severe hypoglycemia (low blood sugar) — only a risk when combined with insulin or sulfonylureas, not when used alone

Important warnings

Hold metformin before any procedure using iodinated contrast dye (CT scan with contrast, angiogram, cardiac catheterization) — contrast can temporarily impair kidney function and increase lactic acidosis risk; restart 48 hours after the procedure once kidney function is confirmed normal

If you become seriously ill, vomit repeatedly, have severe diarrhea, or become unable to eat or drink (the 'sick day' rule) — hold metformin temporarily and contact your pharmacist or doctor

Excessive alcohol intake significantly increases the risk of lactic acidosis — limit alcohol consumption

Have your kidney function (eGFR) checked at least annually — metformin is processed by the kidneys and must be dose-adjusted or stopped if kidney function declines

Long-term use can reduce B12 absorption — ask your doctor about monitoring B12 levels and whether supplementation is appropriate

Who should take extra care

Kidney function: Metformin is stopped below an eGFR of 30 and used cautiously between 30 and 45; kidney function is checked at least yearly.
CT scans and angiograms with contrast: Metformin is held around the procedure and restarted once kidney function is confirmed normal.
Illness, vomiting, or not eating and drinking: The 'sick day' rule — hold it and get advice.
Alcohol: Heavy or regular drinking raises the risk of lactic acidosis.
Long-term use: Vitamin B12 absorption falls in 10–30% of long-term users; levels are worth checking periodically.

Who should not take it

Significant kidney impairment (eGFR below 30 mL/min/1.73m² — must stop; use with caution at eGFR 30–45)
Acute or chronic metabolic acidosis, including diabetic ketoacidosis
Active or planned iodinated contrast dye procedure (CT scan with contrast, cardiac catheterization, angiography) — temporarily hold metformin
Liver disease with significantly impaired liver function — metformin can accumulate
Excessive alcohol consumption
Allergy to metformin

Drug interactions

Iodinated contrast media (used in CT scans and angiograms) — hold metformin for 48 hours before and restart 48 hours after, once kidney function is confirmed normal. Alcohol — increases lactic acidosis risk; avoid heavy drinking. Carbonic anhydrase inhibitors (topiramate, acetazolamide) — increase lactic acidosis risk. Cimetidine (an older antacid/H2 blocker) increases metformin levels significantly — use of modern PPIs (omeprazole, pantoprazole) does not have this interaction. Diuretics and ACE inhibitors that impair kidney function can indirectly increase metformin accumulation.

Commonly asked about alongside Metformin: Ozempic, Jardiance, Mounjaro.

This is not a complete list. If you take several medications, or buy anything over the counter, a pharmacist medication review is the reliable way to catch interactions that matter.

Coverage in British Columbia

Metformin (Glucophage) may be covered under BC PharmaCare depending on your plan. Diabetes medications are covered under the National Pharmacare plan (Plan NP) at no cost for eligible BC residents. Note: some diabetes drugs like saxagliptin, linagliptin, and pioglitazone require Special Authority approval — your doctor must apply before you fill. Ozempic and Metformin do not require Special Authority. Coverage amounts vary — Fair PharmaCare covers 70–100% after your annual deductible depending on your income. Call us at 604-705-3644 and we'll check your specific coverage in minutes. Metformin is already the generic name — there is no brand premium. Full coverage applies under your PharmaCare plan with no brand/generic cost difference. Coverage information is a general guide only. Your actual coverage depends on your PharmaCare plan and eligibility. We check coverage for free — call 604-705-3644 or ask at the counter.

Coverage may depend on indication, PharmaCare plan and Special Authority requirements. Ask Pill4Me Pharmacy to check your coverage, or see BC PharmaCare.

Frequently asked questions

Why does metformin cause stomach upset, and will it go away?

Stomach upset (nausea, diarrhea, cramping) is the most common side effect of metformin, especially when starting or increasing the dose. It occurs because metformin affects the gut directly. Taking it with or after a meal significantly reduces symptoms. Starting at a low dose and increasing slowly (over several weeks) helps your body adjust. Switching to the extended-release formulation (Glumetza or Metformin ER) eliminates GI side effects in most patients. For the majority of people, symptoms improve considerably after the first 2–4 weeks.

Do I need to stop metformin before a CT scan?

Yes — if your CT scan uses intravenous contrast dye (the injected dye that makes organs show up clearly), you should hold metformin for 48 hours before the procedure and restart it 48 hours after, once it has been confirmed your kidneys are working normally. Contrast dye can temporarily impair kidney function, and if kidneys are not clearing metformin effectively, lactic acidosis can occur. Always tell the CT scan booking staff that you take metformin.

Can I drink alcohol while taking metformin?

Occasional, moderate alcohol consumption is generally acceptable, but heavy or regular drinking is a concern. Alcohol and metformin both affect lactic acid metabolism, and combining heavy alcohol use with metformin significantly increases the risk of lactic acidosis. One to two standard drinks on a special occasion is generally fine; daily or heavy drinking should be avoided and discussed honestly with your doctor.

Will metformin cause low blood sugar (hypoglycemia)?

No — when used alone, metformin does not cause low blood sugar. This is one of its advantages over some other diabetes medications. Metformin lowers blood sugar by improving how your body uses insulin and reducing glucose from the liver — not by forcing the pancreas to produce extra insulin. However, if you take metformin together with insulin or a sulfonylurea (glyburide, glipizide), low blood sugar is possible from those other medications.

What is lactic acidosis and how worried should I be?

Lactic acidosis is a rare but serious buildup of lactic acid in the blood. In the context of metformin, it is most likely to occur when the kidneys are impaired (causing metformin to accumulate), when combined with heavy alcohol use, or in severe illness with dehydration. The overall risk is very low in patients with normal or mildly reduced kidney function. Symptoms include unusual muscle pain, breathing difficulty, stomach discomfort, or extreme fatigue — these require immediate emergency care. Regular kidney function monitoring (annually, more often if kidneys are impaired) is the key preventive measure.

Related medications

Ozempic (semaglutide)Jardiance (empagliflozin)Mounjaro (tirzepatide)

Conditions it’s used for

Type 2 Diabetes

Already taking Metformin?

Move your prescription to Pill4Me and we handle the rest — we contact your current pharmacy, and refills, reminders and free local delivery come with it.

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Pill4Me Pharmacy is at 5625 Promontory Rd Unit 101, Chilliwack, BC. We deliver free to Chilliwack, Sardis, Promontory, Vedder and Yarrow, and you can reach a pharmacist directly at 604-705-3644.