Metformin side effects and how to manage them

Many people take metformin to treat type 2 diabetes, manage PCOS, or even—as some Silicon Valley tech pros have reportedly done—as an anti-aging and longevity drug. At the same time, more people are discovering they also are losing weight while taking metformin. As a result, metformin also is often prescribed off-label for weight loss, even among people who don’t have diabetes. Knowing about metformin side effects is a key factor in deciding if this medication is the right choice for your weight journey.  

More prescription medications are now available to help people with excess weight and obesity. That also means that trying to find the best choice for weight management can be confusing. 

Found-affiliated health care providers are trained in obesity medicine, and they can give you the insights you need to navigate your choices for effective weight care using Found’s propriety assessment, MetabolicPrintTM. Each eligible member also receives a personalized prescription and treatment plan to target the root cause of their weight gain. 

What is metformin? 

Approved by the U.S. Food and Drug Administration in 1994 to treat type 2 diabetes, metformin lowers blood sugar levels in three key ways: 

1. Decreases the liver’s production of glucose;

2. Decreases the amount of glucose absorbed from food; and 

3. Increases your body’s response to insulin, which regulates blood sugar. 

Metformin can also aid weight loss by suppressing appetite and reducing visceral fat accumulation (belly fat that surrounds your organs). 

Available as a tablet or liquid, most patients take metformin once or twice a day with meals.

Metformin comes in immediate-release (IR) and extended-release (ER) versions. Metformin brand names include Fortamet®, Glumetza®, Glucophage®, and Riomet®—all of which are FDA-approved diabetes medications. 

What are the most common side effects of metformin? 

While studies published by the American Diabetes Association call metformin effective, safe and well-tolerated, some patients do experience gastrointestinal symptoms. Common metformin side effects include: 

• Diarrhea

• Constipation

• Mild stomach pain or cramping

• Bloating

• Gas

• Indigestion

• Heartburn

• Metallic taste in the mouth

• Headache

• Nail changes

• Flushing of the skin

• Muscle pain

In most cases, these common side effects of metformin subside on their own, and you may want to change how you eat to avoid them. If the side effects persist, worsen, subside and return, or start after taking the medication for a while, talk to your doctor or health care professional. Don’t stop taking metformin until you check with your doctor. 

What are the most serious side effects of metformin?  

Taking metformin can have other consequences as well. These serious side effects of metformin may include: 

• Chest pain

• Rash

• Nausea

• Vomiting

• Hypoglycemia

• Severe stomach pain

• Fatigue or weakness

• Deep, rapid breathing

• Shortness of breath

• Dizziness

• Lightheadedness

• Fast or slow heartbeat

• Significant decrease in appetite

• Feeling cold, particularly in hands or feet

If you experience any of the above symptoms, stop taking metformin and check with your doctor immediately or seek emergency care. 

Metformin warnings

Metformin has a black box warning—the most serious safety-related FDA warning—for the risk of lactic acidosis, a buildup of lactic acid in the bloodstream, which can be life-threatening. 

Symptoms of lactic acidosis include nausea, vomiting, abdominal pain, diarrhea, confusion, ataxia (coordination problems), and fatigue. 

Tell your doctor if you’re over 65 and have kidney disease or kidney problems, have heart or liver disease, had a heart attack, stroke, or heart failure, had diabetic ketoacidosis, or have been in a coma.  

Drug interactions

Metformin may interact with other medications, so notify your doctor if you are taking any of the following:

• Acetazolamide (Diamox®)

• Dichlorphenamide (Keveyis®)

• Methazolamide

• Topiramate (Topamax®, or in Qsymia®)

• Zonisamide (Zonegran®)

• Bupropion

• Carbonic anhydrase inhibitors

• Cephalexin

• Cimetidine

• Dolutegravir

• Ethanol

• Glycopyrrolate

• Iodinated contrast agents

• Lamotrigine

• Ranolazine 

Drinking alcohol may increase the risk of lactic acidosis as well as lower blood sugar, so consult your doctor to find out how much, if any, alcohol you can consume while taking metformin. 

Health care providers often prescribe metformin to treat people with polycystic ovary syndrome (PCOS). It may stimulate ovulation in people with PCOS or those who are premenopausal and cause an increased risk of unintended pregnancy. If you’re in a sexual relationship that can result in pregnancy, use at least one form of birth control unless you’re planning on getting pregnant.  

Metformin is considered to be well-tolerated when taken while pregnant, with no evidence of congenital abnormalities. In addition, breastfeeding while taking metformin has not been linked to adverse side effects in infants. Also, there’s no evidence linking the use of metformin to a reduction in fertility for either women or men on the drug. Talk to your doctor before taking metformin if you’re pregnant, breastfeeding, or planning to become pregnant. 

How long do metformin side effects last?

In general, metformin is considered well-tolerated. Research hasn’t found any significant safety risks for those using metformin for weight loss for up to 10 years. And studies have shown that most metformin side effects often resolve with prolonged use. 

Tips for managing metformin side effects 

To alleviate the side effects of metformin, try the following:  

Drink more water

Staying hydrated can help ward off vomiting and diarrhea. Instead of drinking a full glass of water all at once, take small sips of water frequently throughout the day.

Take metformin with food 

Taking metformin with food can help reduce or eliminate nausea. 

Eat small, frequent meals

Eating smaller meals more often during the day can help prevent loss of appetite and stomach aches. Using a heating pad also could help alleviate stomach aches. 

Chew sugar-free gum

If you have a metallic taste in your mouth, try chewing sugar-free gum to eliminate it. 

Take vitamin B12 supplements 

In some cases, taking metformin long-term can lead to a vitamin B12 deficiency. Call your doctor if you experience tiredness, muscle weakness, mouth ulcers, sore tongue, vision problems, and pale or yellow skin. You may need to take vitamin B12 supplements, but consult your provider for medical advice if you need to increase your vitamin B12 levels.  

Taking metformin to lose weight 

While taking metformin to lose weight can help people reach their goals, it may not be for everyone. Getting a personalized prescription and treatment plan for medical weight loss is crucial. Furthermore, if you’re using metformin for weight control, it’s important to take it under the care of a health care provider who specializes in obesity medicine and who can monitor your progress. Your requirements may change as you lose weight, and a clinician trained in weight care can help you adjust your prescription as needed.

Found-affiliated clinicians can help you create a personalized treatment plan for your weight journey. In addition to prescription medication, Found offers health coaching, a supportive community, and an in-app program with guidance for lifestyle changes to help you reach your goals. To get started, take the MetabolicPrintTM quiz to discover your unique MetabolicPrint profile. Your Found clinician will use your profile, along with your medical history and lab work, to begin the process of finding your personalized prescription. 

About Found

To discover your MetabolicPrint and start your journey with Found, take our quiz. Found is among the largest medically supported weight care clinics in the country, having served more than 200,000 members to date.

GLP-1*

GLP-1 prescriptions, filled through your local pharmacy, are now available as part of Found's weight-loss toolkit. While GLP-1s can be effective for weight loss, they are not clinically appropriate for everyone. Eligibility for a GLP-1 is based on a thorough evaluation of your medical history and lab work. If a GLP-1 is not appropriate for you, our providers will work with you to determine an effective medication for your health profile.