Drug Information Guide
Biguanide antidiabetic·#20 most prescribed in Canada

Glucophagemetformin hydrochloride

Also known as: Glumetza (extended-release), Glycon, Riomet (liquid), Metformin (multiple generics)

Metformin is the #1 first-line treatment for type 2 diabetes in Canada. Learn about dosing, stomach side effects, CT scan interactions, and BC coverage at Pill4Me.

Prescriptions (Canada 2024)

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

Drug class

Biguanide antidiabetic

DIN (Canada)

02229949, 02229950 +1 more

What is Glucophage?

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 it 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 & 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 to take it

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.

Side effects

Common side effects

  • 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

Serious side effects — seek care immediately

  • 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 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.

BC PharmaCare coverage

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 details change — confirm with your Pill4Me pharmacist or visit 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)Synthroid (levothyroxine sodium)

Questions about Glucophage?

Our Chilliwack pharmacists can review your medications, check for interactions, and answer any questions — at no charge.

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Medical disclaimer: This page is for general educational purposes only and does not constitute medical advice. Always consult your pharmacist or prescriber before making any changes to your medications. BC PharmaCare coverage criteria are subject to change.