Does Metformin help with weight loss?

Many drugs impact your body in more ways than one. Take acetaminophen. You could use it to lower your fever, but you could also use it to ease a tension headache. Metformin is similarly multitalented. Approved by the FDA to treat type 2 diabetes by lowering blood sugar, metformin can also lead to weight loss. Here's a look at how this drug works, along with side effects, cost, and more.

What is metformin?

Metformin is a generic medication that's been used since the 1950s in Europe and Canada for managing blood sugar in people with diabetes. In the U.S., the FDA approved it in 1994 and, since then, it’s become one of the most widely prescribed diabetes medications in the country.

It works by helping your body respond better to insulin — a hormone that regulates blood sugar — and decreases the amount of sugar your liver produces and limits how much sugar your body absorbs from food, keeping it out of your blood stream. On average, most patients find their A1c levels (a way to measure blood sugar over time) drop by up to 1.5%.

Metformin brand names

Metformin is a generic name for a drug that can either be prescribed on its own or under a brand name that contains other active ingredients. For example, metformin may be combined with medications like linagliptin, saxagliptin, pioglitazone, or repaglinide — which all have an additional effect on insulin release that strengthens the body’s reaction. Some FDA-approved medicines that contain metformin include:

• Actoplus
• Avandamet
• Fortamet
• Glucophage
• Glucovance
• Glumetza
• Invokamet
• Janumet
• Jentadueto
• Kazano
• Kombiglyze
• Prandimet
• Riomet
• Synjardy
• Xigduo

Metformin uses

Metformin is primarily used for its FDA-approved purpose: type 2 diabetes management. This is thanks to its ability to help regulate blood sugar, according to Dr. Brian Lake, D.O., an endocrinologist who's board-certified in diabetes and metabolism with a practice in Largo, Florida. But its uses don’t stop there.

What is metformin used for?

In addition to treating type 2 diabetes, metformin may be prescribed at a doctor’s discretion off-label for other purposes, including treating prediabetes, regulating menstrual cycles in people with polycystic ovary syndrome (PCOS), and managing blood sugar in pregnancy for women with gestational diabetes.

Because weight loss is a common side effect of the medication, it may also be prescribed off-label for that use, according to Dr. Pooja Gidwani, M.D., a Los Angeles-based internist and obesity specialist. "People with insulin resistance — such as those with prediabetes, PCOS, or type 2 diabetes — often experience a gradual four to seven pound weight loss, but the response is highly individual,” Gidwani says. "Metformin is not a weight-loss drug per se, and expectations should reflect that.”

That said, some people may lose a more significant amount. Research examining the impact of metformin on weight in people without diabetes found that 30% lost more than 5% of their weight over the course of a year and kept it off.

How does metformin work?

Glucose, which is another word for blood sugar, is made in the liver when your body needs it. Metformin decreases how much glucose the liver produces and, as a result, lowers your blood glucose. It also may improve insulin sensitivity and slows the rate of food absorption, which can keep blood sugar from getting too high when you eat.

The medication also alters how quickly you absorb carbohydrates and how efficiently your body handles glucose. Those play a role in regulating your blood sugar and may have an effect on weight as well.

"For many years, we considered metformin to be weight-neutral," says Lake. "Now we know that metformin causes weight loss through multiple ways.” Those include a change in appetite regulation — helping you feel full for longer — and benefits with gut bacteria. It may even help with energy expenditure, Lake adds, which means you burn calories at a slightly faster rate.

Metformin dosage

The dosage you end up taking will depend on your particular health needs and what you're trying to address, says Lake. The starting dose is 500 mg, and there are several higher strengths that you may progress toward if that dosage is not effective enough.

Forms and strengths

There are two formulations available: immediate-release, which is taken twice per day, and extended-release, which is taken once-daily, typically with an evening meal. You'll know if the metformin is an extended-release version because the brand name will have XR after it. For example, Glucophage is immediate release, and Glucophage XR is extended release.

In terms of strengths, metformin comes in these options: 500 mg, 625 mg, 750 mg, 850 mg, 1000 mg.

Metformin side effects

Metformin is generally considered safe and well-tolerated, but some people may feel certain side effects on it, says Lake. These side effects can range from mild to potentially severe, and they tend to occur most when you first start taking the medication, as your body gets used to the drug, he adds.

Common side effects

The most common effects for metformin are gastrointestinal, says Gidwani. That's because metformin's mechanisms of action are centered in the GI tract. You may experience:

• Bloating or gas
• Constipation
• Diarrhea
• Headache
• Metallic taste in your mouth
• Nausea or vomiting

"The risk of side effects are low with the medication and generally do not give much cause for concern," says Lake. "But if the GI side effects are not tolerable, a lower dose of metformin or another class of medication may be considered."

For a full list of metformin side effects, look at the medications prescribing information (for example, here is the prescribing information for Glucophage).

Serious side effects

While much less common, some people may experience more severe side effects when taking metformin, particularly when they stay on it for a long time. Some serious effects include:

• Lactic acidosis: The most serious complication with metformin is lactic acidosis, a buildup of lactic acid in the blood that can be fatal, says Gidwani. Signs include nausea, fatigue, rapid breathing, and muscle cramps. More advanced symptoms are confusion, increasing weakness, and difficulty with coordination.
  
  
• Vitamin B12 deficiency: Long-term use of metformin is also associated with vitamin B12 deficiency, which can lead to fatigue, cognitive symptoms, nerve damage, or anemia, says Gidwani.
  
  
• Hypoglycemia: Although metformin has lower risk of hypoglycemia (low blood sugar) than other oral antidiabetes drugs, there is still a chance this can occur. Signs include feeling shaky, fast heartbeat, lightheadedness, hunger, nausea, and sweating.

Alternatives to metformin

If you’re taking metformin for type 2 diabetes and it’s either not managing blood sugar well or causing severe side effects, alternatives include pioglitazone and acarbose, both of which can help regulate your blood sugar. You may also look into GLP-1 receptor agonists, such as semaglutide (Ozempic) and tirzepatide (Mounjaro).

If you’re using metformin off-label for weight loss and it’s not giving you the results you’re looking for, you have alternatives as well. Those same GLP-1s used for diabetes management have versions approved for weight loss: Wegovy for semaglutide and Zepbound for tirzepatide. These are both more effective and consistent for weight loss than metformin, Gidwani says. These medications not only drive greater fat loss but also offer cardiovascular and anti-inflammatory benefits (although at a steeper price than metformin).

If needles aren’t your thing (or you can’t afford GLP-1s), Gidwani says you can also combine metformin with a weight-loss medication like buproprion-naltrexone. That combination of an opioid antagonist drug and an anti-depressant reduces cravings and hunger.

Metformin warnings and precautions

Metformin is not recommended for people with advanced kidney disease, significant liver impairment, or a history of lactic acidosis, Gidwani says. It should also be used cautiously in individuals with heart failure, severe dehydration, alcohol use disorder, or acute infections — especially if you aren’t eating much or are throwing up often. These are all situations where the risk of lactic acidosis increases.

The FDA has also issued what's called a black box warning — which alerts consumers to a drug’s most serious precautions — about two of metformin's potentially serious side effects: lactic acidosis and hypoglycemia.

Metformin interactions

Metformin has relatively few interactions, but there are some essential ones to know, says Lake.

For instance, if you’re doing an imaging study and need to have contrast dye, you’ll be asked to stop taking metformin temporarily. That’s because the dye can impact kidney function briefly, and it’s stressful on the body to have to clear both the dye and the metformin simultaneously.

You may also need to change a medication that impacts your kidney function, like a diuretic or ACE inhibitor, if you’re also taking metformin, Gidwani adds.

Metformin cost

Unlike GLP-1s, which are brand names and can cost more than $1,000 a month, metformin is a generic medication that can be pretty affordable for people paying out-of-pocket. Your exact cost will vary depending on your pharmacy, but qualified members of WW Clinic can get it for free with membership.

As for insurance, it’s likely to cover metformin when it’s prescribed for type 2 diabetes. If metformin is prescribed off-label for weight loss, it’s less likely insurance will cover it. But that may not matter as much due to its low out-of-pocket price.

The bottom line

FDA-approved for type 2 diabetes management, metformin is a pill that’s been used in this country for more than 20 years. In addition to regulating blood sugar, metformin may also result in a modest weight loss, which has led some providers to prescribe it off-label for that purpose.

The drug affects weight in several ways, including reducing appetite, improving gut regulation, and increasing energy expenditure so that you burn more calories in general. Keep in mind that not everyone experiences weight loss when using metformin, so you may want to talk to your provider about alternatives if you aren’t seeing the results you want.