Metformin side effects and how to avoid them

In this article:

• Common side effects
• Serious side effects
• Warnings
• Interactions
• Managing side effects
• Metformin vs. metformin ER

In this article

• Common side effects
• Serious side effects
• Warnings
• Interactions
• Managing side effects
• Metformin vs. metformin ER

Metformin is an oral medication commonly prescribed to treat Type 2 diabetes and prediabetes. It helps to control blood glucose levels and restore the body’s response to insulin. When someone is first diagnosed with Type 2 diabetes, metformin is one medication that is often recommended along with diet and exercise. However, it can cause side effects, especially in the stomach and bowels. Here, we’ll look at possible common and more serious side effects of metformin and discuss how some of them can be managed. 

Common side effects of metformin

Metformin lowers blood sugar by slowing down the release of glucose from the liver into the bloodstream. It also slows glucose absorption and helps the body use insulin more effectively. 

As with any medication, metformin has the potential for side effects. Taking metformin with food can help to reduce some of them. Common side effects of metformin include: 

• Diarrhea
• Nausea or vomiting
• Upset stomach
• Gas
• Low energy
• Headache
• Low vitamin B12 levels

Less commonly, people may also experience:

• Metallic taste in the mouth
• Weight loss
• Loss of appetite
• Low blood sugar, especially when taken together with other diabetes medications or insulin
• Dizziness
• Shortness of breath or chest pain
• Skin or nail problems
• Body aches
• Sweating or chills
• Heart racing 

Many of metformin’s side effects are more common when someone first starts taking it. For some people, these side effects go away after their body adjusts to the medication. For others, side effects may continue or become worse. Some metformin side effects, like low vitamin B12 levels, don’t always have symptoms, so regular checkups are essential. 

Most people who take metformin alone don’t have trouble with low blood sugar. It’s one of the advantages of metformin. But, people who take it with insulin or other diabetes drugs, like sulfonylureas, may have a higher risk of low blood sugar. Signs of hypoglycemia include dizziness, shaking, confusion, fatigue, and fainting.

Metformin is sometimes prescribed off-label to women with polycystic ovary syndrome (PCOS), a condition that can cause hormone imbalance, higher blood sugar levels, and irregular periods. Metformin may lead to more regular ovulation for women with PCOS. This is a benefit for people who are being treated for infertility. But those who choose not to become pregnant should also be aware of this as a side effect.

Serious side effects of metformin 

Lactic acidosis is a very rare but serious side effect of metformin that requires emergency medical attention. It almost never occurs when metformin is taken as directed under the care of a healthcare professional. The risk factors for lactic acidosis with metformin include:

• Advanced kidney disease
• Liver disease
• Drinking excessive amounts of alcohol
• In certain medical or surgical settings, such as not eating before or after surgery or getting IV contrast for radiology studies
• Taking large amounts of metformin

Signs and symptoms of lactic acidosis include:

• Dizziness or lightheadedness
• Muscle pain
• Extreme weakness or tiredness
• Trouble breathing 
• A fast or slow heart rate
• Flushing of the skin
• Decreased appetite
• Severe stomach pain

Although it’s rare, metformin may cause allergic reactions. Signs of an allergic reaction include difficulty breathing, swelling of the face or hands, and a skin rash. Seek immediate medical attention if you believe you’re experiencing an allergic reaction. 

 Taking metformin for extended amounts of time may lead to a vitamin B12 deficiency. Over time, this can lead to anemia and other health problems. People taking metformin should have regular blood tests that include vitamin B12 levels. 

Metformin warnings 

 Metformin is FDA-approved for adults and children 10 and older. Adults over 65 may need more frequent checks for conditions that could increase the risk of side effects.

Metformin should not be used or used with caution in people who:

• Have liver or kidney disease
• Have heart failure
• Are not able to eat for a period of time
• Are getting ready for surgery or just after surgery
• Drink a lot of alcohol
• Will be having a CT scan or other study that uses IV contrast solution

People with diabetes should have regular checkups and lab tests as directed by their doctor. This can prevent the most serious side effects of metformin.

Metformin is not used to treat Type 1 diabetes. Only insulin treats Type 1 diabetes. 

Metformin is considered generally safe to use during pregnancy and breastfeeding. However, a doctor will reassess the best treatment plan for safety and effectiveness during pregnancy.

Metformin interactions

People who use insulin or other diabetes medications together with metformin may be at higher risk of low blood sugar.

Some medications can increase the risk of side effects. Others can make metformin less effective.

“Metformin can interact with other medications, including diuretic medications, steroid medications, certain thyroid drugs, oral contraceptives, and calcium channel blocking drugs like nifedipine,” says Chirag Shah, MD, and co-founder of Push Health, an online healthcare platform. “Due to a wide range of medication interactions, it is important to review a patient’s current medications before prescribing metformin.”

Medications that may decrease the effectiveness of metformin include:

• Quinolone antibiotics such as ciprofloxacin and levofloxacin
• Thiazide diuretics such as hydrochlorothiazide and chlorthalidone
• Some calcium channel-blocking blood pressure medications, such as verapamil and nifedipine
• Steroids such as prednisone

Medications that may increase the risk of serious side effects through liver or kidney damage: 

• IV contrast medication given before some MRIs, X-rays, or CT scans 
• Excessive alcohol
• High doses or long-term use of non-steroidal anti-inflammatory drugs (NSAIDs) like ibuprofen or naproxen

Interactions that may increase the risk of lactic acidosis:

• Glaucoma drugs acetazolamide, dichlorphenamide, and methazolamide
• Topiramate
• Zonisamide

People taking thyroid medication may also need to monitor thyroid levels more closely.

Metformin may be prescribed on its own as a generic medication. Or it may be prescribed as part of a brand-name combination pill such as Janumet, Invokamet, Actoplus Met, and Synjardy. Ask your healthcare provider or pharmacist whether your combination pills contain metformin.

To avoid drug interactions with metformin, talk with your healthcare provider about all prescription and over-the-counter (OTC) medications you take. Include vitamins and supplements.

Managing metformin side effects

Take metformin only as the dosage and schedule recommended by your healthcare provider.

Some of the more common side effects may be managed by:

• Starting at a low dose and increasing slowly
• Taking it with meals
• Switching to an extended-release version of metformin

To prevent the more serious side effects of metformin, keep regular appointments for follow-up visits and lab tests. This will help ensure that no changes occur that may increase the risk of side effects.

Metformin vs. metformin ER

Metformin and metformin extended-release (ER) are essentially the same medication, but the body absorbs the ER version more slowly. It’s usually taken only once a day instead of twice.

Just like regular metformin, metformin ER should only be taken as directed by your healthcare provider. The potential medication interactions and side effects are similar, but the risk of GI side effects is lower with metformin ER.