Many medications can cause side effects. A side effect is an unwanted response to a medication when it is taken in normal doses. Side effects can be mild or severe, temporary or permanent.

The side effects listed below are not experienced by everyone who takes Glucophage (Metformin). If you are concerned about side effects, discuss the risks and benefits of Glucophage (Metformin) with your doctor.

The following side effects have been reported by at least 1% of people taking Glucophage (Metformin). Many of these side effects can be managed, and some may go away on their own over time.

Contact your doctor if you experience these side effects and they are severe or bothersome. Your pharmacist may be able to advise you on managing side effects.

• Diarrhea
• dizziness or lightheadedness
• increased sensitivity of skin to the sun
• loss of appetite
• metallic taste in mouth
• nausea
• passing of gas
• stomach ache
• vomiting
• weight loss

Although most of the side effects listed below don't happen very often, they could lead to serious problems if you do not check with your doctor or seek medical attention.

Check with your doctor as soon as possible if any of the following side effects occur:

• decreased coordination
• feeling cold
• feeling extremely weak, tired, or uncomfortable
• low blood sugar (mild), including:
• anxiety
• behavioural changes similar to being drunk
• blurred vision
• cold sweats
• confusion
• cool, pale skin
• difficulty concentrating
• drowsiness
• excessive hunger
• fast heartbeat
• headache
• nausea
• nervousness
• nightmares
• restless sleep
• shakiness
• slurred speech
• peripheral Neuropathy (e.g., numbness, prickling, tingling in hands or feet)
• signs of Anemia (low red blood cells; e.g., dizziness,  pale skin, unusual tiredness or weakness, shortness of breath, rapid heartbeat, dark urine)
• slow or irregular heart beat
• thinking difficulties (e.g., poor decision making, decreased concentration, twitching, trembling, trouble speaking or swallowing)
• trouble breathing
• unusual muscle pain

Stop taking the medication and seek immediate medical attention if any of the following occur:

• lactic acidosis (quick and severe), including:
• fast, shallow breathing
• muscle pain or cramping
• slow or irregular heartbeat
• unusual sleepiness
• unusual stomach ache (after the initial stomach ache that can occur at the start of therapy)
• unusual tiredness or weakness

• seizure
• signs of pancreatitis (e.g., abdominal pain on the upper left side, back pain, nausea, Fever, chills, rapid heartbeat, swollen abdomen)

Some people may experience side effects other than those listed. Check with your doctor if you notice any symptom that worries you while you are taking Glucophage (Metformin).

500 mg
Each white, round, biconvex tablet, scored on one side and debossed with "HMR" on the other, contains Glucophage (Metformin) HCl 500 mg. Nonmedicinal ingredients: magnesium stearate and povidone; tablet coating: hydroxylpropyl methylcellulose, titanium dioxide, and polyethylene glycol.

850 mg
Each white, oblong tablet, debossed with "HMR" on one side and "850" on the other, contains Glucophage (Metformin) 850 mg. Nonmedicinal ingredients: magnesium stearate and povidone.

Do not take Glucophage (Metformin) if you:

• are allergic to Glucophage (Metformin) or any ingredients of Glucophage (Metformin)
• are experiencing or recovering from severe infections, trauma, or surgery
• are pregnant or breast-feeding
• are suffering severe dehydration (have lost a lot of water from your body)
• are undergoing radiologic studies involving use of iodinated contrast materials
• drink large amounts of alcohol in the short term or on a regular basis
• have a history of lactic acidosis
• have acute/chronic metabolic acidosis (too much acid in the blood), diabetic ketoacidosis with or without coma, or history of ketoacidosis with or without coma
• have diseases associated with lack of oxygen to the tissues such as cardio-respiratory insufficiency
• have reduced kidney function
• have severe liver disease
• have Type 1 Diabetes (people with type 1 diabetes should always be using insulin)
• have very poor blood glucose control (these people should not take Glucophage (Metformin) as the only antidiabetic agent)

There may be an interaction between Glucophage (Metformin) and any of the following:

• Acetazolamide
• acetylsalicylic acid (Asa)
• alcohol
• angiotensin converting enzyme inhibitors (ACEIs; Captopril, Enalapril, Ramipril)
• antipsychotics (e.g., Clozapine, Olanzapine, Quetiapine, Risperidone)
• beta 2 agonists (e.g., salbutamol, formoterol, terbutaline)
• birth control pills
• Brinzolamide
• Bupropion
• calcium channel blockers (e.g., Amlodipine, Diltiazem, Nifedipine, Verapamil)
• Cephalexin
• Cimetidine
• corticosteroids (e.g., Dexamethasone, Prednisone)
• Danazol
• decongestants (e.g., phenylephrine, Pseudoephedrine)
• diabetic drugs (e.g.,  Glyburide, insulin, Repaglinide, Sitagliptin)
• Disopyramide
• diuretics (water pills; e.g., Amiloride, Furosemide, Hydrochlorothiazide)
• dofetilide
• dolutegravir
• estrogens (e.g., conjugated estrogen, Estradiol, ethinyl estradiol)
• Glucagon
• glycopyrrolate
• Hepatitis C antivirals  (e.g., dasabuvir, ombitasvir, paritaprevir, ritonavir)
• HIV protease inhibitors (e.g., atazanavir, indinavir, ritonavir, saquinavir)
• iodinated contrast material
• Lamotrigine
• Lanreotide
• mifepristone
• monoamine oxidase inhibitors (M.O.S. e.g., Moclobemide, Phenelzine, Rasagiline, Selegiline, Tranylcypromine)
• nicotinic acid (Niacin)
• Octreotide
• Ondansetron
• Pasireotide
• Pegvisomant
• pentamidine
• Phenytoin
• procainamide
• progestins (e.g., Dienogest, Levonorgestrel, medroxyprogesterone, Norethindrone)
• quinine
• quinolone antibiotics (e.g., ciprofloxacin, Norfloxacin, Ofloxacin)
• selective serotonin reuptake inhibitors (SSRIs; e.g., Citalopram, Fluoxetine, Paroxetine, Sertraline)
• Somatropin
• sulfonamide antibiotics ("sulfas"; e.g., sulfisoxazole, sulfamethoxazole)
• Sunitinib
• Tacrolimus
• testosterone
• Thyroid products
• Topiramate
• Trimethoprim

If you are taking any of these medications, speak with your doctor or pharmacist. Depending on your specific circumstances, your doctor may want you to:

• stop taking one of the medications,
• change one of the medications to another,
• change how you are taking one or both of the medications, or
• leave everything as is.

An interaction between two medications does not always mean that you must stop taking one of them. Speak to your doctor about how any drug interactions are being managed or should be managed.

Medications other than those listed above may interact with Glucophage (Metformin). Tell your doctor or prescriber about all prescription, over-the-counter (non-prescription), and herbal medications you are taking. Also tell them about any supplements you take. Since caffeine, alcohol, the Nicotine from cigarettes, or street drugs can affect the action of many medications, you should let your prescriber know if you use them.

Before you begin taking a medication, be sure to inform your doctor of any medical conditions or Allergies you may have, any medications you are taking, whether you are pregnant or breast-feeding, and any other significant facts about your health. These factors may affect how you should take Glucophage (Metformin). 

Alcohol intake: Anyone taking Glucophage (Metformin) should avoid excessive alcohol intake.

Blood sugar control: If you have fever, trauma, infection, or surgery, you may have a temporary loss of blood sugar control. At such times, your doctor may think it is necessary to stop Glucophage (Metformin) and temporarily inject insulin. Glucophage (Metformin) may be started again after the problem is resolved.

Blood sugar monitoring: Monitor your blood sugar regularly at intervals as discussed with your doctor or diabetes educator.

Diabetes complications: The use of Glucophage (Metformin) (or any other medication used for diabetes) will not prevent the development of complications particular to diabetes mellitus (e.g., Kidney Disease, nerve disease, eye disease).

Diet: Glucophage (Metformin) is a treatment to be taken in combination with a proper diet. Glucophage (Metformin) is not a substitute for proper diet.

Dye or contrast agents: If you are going to have an X-ray procedure that uses dye or a contrast agent, you may need to stop taking Glucophage (Metformin) for a short time. Contact your doctor for instructions.

Kidney problems:  Kidney disease or reduced kidney function causes Glucophage (Metformin) to build up in the body, causing side effects. If you have kidney problems, your doctor should closely monitor your condition while you are taking Glucophage (Metformin), as it may affect kidney function.

Lactic acidosis: Lactic acidosis is a rare but serious problem that occurs due to Glucophage (Metformin) accumulation (i.e., the body doesn't get rid of it fast enough) during treatment. If you have severe kidney disease you are at higher risk of developing lactic acidosis. Since alcohol may increase the risk of lactic acidosis, do not drink a lot of alcohol over the short- or long-term while taking Glucophage (Metformin). When it does occur (very rarely), it is fatal in 50% of cases. There have been no reports of lactic acidosis in Canada when Glucophage (Metformin) was used as directed. If you experience symptoms of lactic acidosis (e.g., weakness, tiredness, drowsiness, unusual muscle pain, trouble breathing, stomach pain with nausea, vomiting or diarrhea, feeling cold, dizziness, light-headedness, or slow or irregular heartbeat), stop taking Glucophage (Metformin) and get immediate medical attention.

Liver function: Decreased liver function has been linked to lactic acidosis. Glucophage (Metformin) is not recommended for people with severely reduced liver function. If you have moderately reduced liver function, discuss with your doctor how Glucophage (Metformin) may affect your medical condition, how your medical condition may affect the dosing and effectiveness of Glucophage (Metformin), and whether any special monitoring is needed.

Low blood sugar: Under usual circumstances, low blood sugar does not occur for people who take only Glucophage (Metformin). Low blood sugar could occur when not enough food is eaten, especially when strenuous exercise is undertaken at the same time or when large amounts of alcohol have been consumed.

Reduced response: Over a period of time, you may become progressively less responsive to a particular treatment for diabetes because your diabetes worsens. If Glucophage (Metformin) fails to lower blood sugar to target levels, talk to your doctor. Your doctor may want to stop Glucophage (Metformin) or recommend another medication.

Surgery: Glucophage (Metformin) should be stopped temporarily for surgery (except for minor surgery where food and fluid intake is not restricted). You will be restarted on Glucophage (Metformin) once you are eating and drinking and your kidney function has been tested and is normal. Talk to your doctor for specific instructions.

Vitamin B12 levels: Glucophage (Metformin) may decrease vitamin B12 levels. Your doctor will monitor your B12 levels with blood tests while you are taking Glucophage (Metformin).

Pregnancy: Glucophage (Metformin) should not be used during pregnancy. If you become pregnant while taking Glucophage (Metformin), contact your doctor immediately.

Breast-feeding: Glucophage (Metformin) is believed to pass into breast milk. Glucophage (Metformin) should not be used if you are breast-feeding.

Children: The safety and effectiveness of Glucophage (Metformin) have not been established for children.

Seniors: Kidney function often decreases with age. As a result, seniors may be more likely to experience side effects of Glucophage (Metformin).