Metformin is a medication used to control blood glucose (sugar) levels in people with type 2 diabetes. It is often taken alongside other anti-diabetic drugs and is most effective when combined with regular exercise, healthy eating habits, and weight control.
A doctor may also prescribe metformin to treat prediabetes and gestational diabetes.
Metformin is available under brand names like Fortamet, Glumetza, Riomet, and Glucophage.
How does metformin work?
It controls blood sugar levels in 3 different ways, which are:
- Reducing how much glucose your liver makes.
- Reducing the amount of glucose your intestines absorb from what you eat and drink.
- Improving sensitivity of your body’s cells to insulin. Insulin is the hormone that signals your cells to take up glucose from the blood.
Who should not take metformin?
While metformin is safe for most people, some people may need to take it with caution or avoid it entirely. It shouldn’t be taken by people who:
- Have a known allergy to it
- Have severe kidney disease
- Have metabolic acidosis—a condition where acid builds up in your body. This includes diabetic ketoacidosis (DKA), a form that occurs in people with diabetes due to lack of insulin.
- Are under 10 years
You will need to take metformin with caution if you:
- Have liver disease
- Have congestive heart failure
- Are 65 years or older
- Take too much alcohol
- Are breastfeeding
If you’re already on metformin, it will be discontinued if you’re going to have surgery or a dye injected into your veins or joints just before an X-ray, MRI, or CT scan is done.
You might also receive instructions to discontinue the drug or take it safely if you have a severe infection or serious vomiting, diarrhea, and dehydration.
What are the side effects of metformin?
Common side effects include:
- Diarrhea
- Passing gas
- Nausea and vomiting
- Stomach pain
- Headache
- Metallic taste
- Tiredness
The medication can also cause less common but serious side effects, like:
Allergic reactions
Metformin-associated allergic reactions can be life-threatening. Seek immediate medical attention if you notice symptoms like:
- Difficult or noisy breathing
- Swelling of the lips, face, tongue, or throat
- Itchy bumps on the skin
- Dizziness or fainting
Lactic acidosis
This is where lactic acid builds up in your blood. It affects normal functions and can be fatal. Its symptoms include:
- Muscle weakness and pain
- Fast, labored breathing
- Lightheadedness
- Vomiting
- Fast, pounding heartbeat
- Stomach pain
Low blood sugar (hypoglycemia)
You are at increased risk of getting hypoglycemia if you use metformin with insulin or other anti-diabetic medications that increase your body’s own insulin. Common hypoglycemia symptoms are:
- Sweating
- Anxiety
- Hunger
- Headache
- Blurry vision
- Irritability
- Seizures
- Confusion
Low vitamin B12 levels
Metformin can reduce the amount of vitamin B12 your body absorbs from food, potentially leading to a deficiency over time. Symptoms of vitamin B12 deficiency include:
- Abnormal heart beat
- Muscle weakness
- Difficulty concentrating
- Numbness or tingling in the hands and feet
- Confusion
- Pale skin
How can I use metformin safely?
Take it as directed by your doctor or pharmacist. Do not share your medication with someone else, and don’t change your medication frequency and amount to mirror someone else’s prescription.
It can be taken as an oral solution or oral tablets. Tablets can be immediate-release or extended-release (meaning they release the medication into the body over a prolonged period of time). Swallow extended-release tablets whole. Do not break, crush, chew, or cut them.
Before taking the liquid form of metformin, shake it well. Use a measuring device recommended by a doctor or pharmacist to measure the dose of medication to take.
Unless instructed otherwise by your doctor or pharmacist, it’s usually advisable to take metformin with a meal to decrease the risk of gut irritation.
If you have symptoms of low blood sugar, take a source of fast-acting sugar, such as hard candy, regular soda, glucose tablets, or glucose packets.
Store your medication at room temperature in a dry place away from kids and pets. To get rid of expired or unwanted medicines safely, read the medication instruction sheets or contact your pharmacist for help.
If you have not yet gone through menopause, metformin can increase your chances of getting an unintended pregnancy. Talk to a doctor about your risk.
What medications can interact with metformin?
Before taking any medicines or supplements with metformin, talk to your doctor or pharmacist. Certain drugs and supplements can affect how metformin works or alter its levels in your blood. Common examples include:
- Cimetidine
- Cephalexin
- Carbonic anhydrase inhibitors, like acetazolamide and methazolamide
- Other anti-diabetes drugs
- Dolutegravir
What should I do if I miss a dose of metformin?
Take your missed dose as soon as you can. If it’s almost time for your next dose, take only that one. Do not take more than one dose at a time.
What if I take more metformin than I have to?
If you have taken too much of the medication, seek medical attention immediately or call a poison control center.
What should I remember?
Metformin is a widely used and well-studied medication for managing type 2 diabetes. It can be used alone or with other diabetes medications.
It works by improving how your body uses insulin and lowering how much glucose comes from your liver and the food you eat.
While generally safe, metformin isn’t for everyone. Always take it as prescribed and consult your doctor before combining it with other drugs or supplements.
