Does Metformin Help With Weight Loss? The Facts

What is Metformin?

Metformin is an oral medication that has been used to treat type 2 diabetes for over 60 years. It belongs to a class of drugs called biguanides, which work by lowering blood sugar levels in several ways:

• Reducing the amount of glucose produced by the liver
• Increasing the sensitivity of muscle cells to insulin so they can absorb glucose from the bloodstream more effectively
• Slowing the breakdown of carbohydrates in the intestines so that glucose is absorbed into the bloodstream more slowly.

In addition to being used for diabetes, metformin has also been used "off-label" for weight loss and metabolic syndrome. However, it has not been approved for these uses by the U.S. Food and Drug Administration (FDA).

How Metformin Promotes Weight Loss

Although metformin is not approved for weight loss, it is a common side effect of the drug. There are several ways metformin may lead to weight loss:

1. Appetite Suppression

Some evidence suggests metformin may blunt appetite. In a 2014 study, people who took metformin reported feeling less hungry and more full compared to those not taking the drug.

Its thought the metformin may act on receptors in the brain that regulate appetite. By inhibiting appetite, it may reduce overall calorie intake which can lead to weight loss.

2. Changes in Gut Bacteria

Metformin seems to cause favorable changes in the bacteria that live in the gut (the gut microbiome). Specifically, metformin increases the number of beneficial bacteria that are linked to improved blood sugar control and decreased weight.

Theres also evidence that certain gut bacteria may contribute to weight control by increasing hormones that promote fullness, like GLP-1 and PYY. By altering gut bacteria, metformin may support weight loss through appetite and hunger mechanisms.

3. Decreased Fat Absorption

Some research shows metformin may reduce the absorption of fat from the digestive tract. In a rodent study, metformin caused a fatty acid called oleic acid to be excreted in feces rather than absorbed into the body.

If the same thing happens in people, it could mean less dietary fat gets absorbed into the body, potentially decreasing overall calorie intake.

4. Changes in Metabolism

Metformin seems to shift metabolism into a mode that prefers sugar as an energy source rather than fat. It does this primarily through activation of an enzyme called AMPK.

AMPK senses when cells are low on energy and then stimulates processes that produce more energy. It turns on glucose uptake, fat burning, and cellular recycling while turning off fat production and storage.

By activating this enzyme, metformin may decrease fat storage and increase the use of fat for energy. This shift in fuel source could promote weight loss.

Typical Dosage of Metformin for Weight Loss

For diabetes, the typical metformin dose ranges from 5002000 mg per day. Doses are often divided throughout the day.

For weight loss in non-diabetics, doctors sometimes prescribe metformin off-label at a dose of 750 mg twice per day (1500 mg total daily dose). However, 500 mg twice per day is also commonly used.

In research studies where metformin is used specifically for weight loss in non-diabetics, the dose has ranged from 15002550 mg per day.

Its unclear if higher doses lead to more weight loss, but 1500 mg per day seems adequate based on current evidence.

How Much Weight Can You Lose on Metformin?

On average, people lose about 28 pounds (about 13.5 kg) over 36 months while taking metformin.

In a clinical study of obese non-diabetics, those randomized to take metformin lost around 5 pounds (2.4 kg) over 16 weeks compared to a placebo group that gained 1 pound (0.5 kg).

Other studies show more modest weight loss, ranging from 26 pounds (about 12.5 kg) over periods from 46 months.

The amount of weight lost on metformin depends on many factors like diet, exercise, dosage, genetics, and more. But for most people, the clinical trials indicate metformin can promote a modest degree of weight loss.

Metformin for Weight Loss in Overweight or Obese People

Metformin appears most effective for weight loss in people who are obese or overweight.

For example, one study looked at metformin for weight loss in obese teens who were not diabetic. After 6 months, the metformin group lost 4.5% of their body weight compared to 0.01% in the placebo group.

In another trial, overweight and obese non-diabetic adults were randomized to receive metformin at 1700 or 2000 mg per day or a placebo. After 6 months, those given metformin had lost around 6 pounds (2.7 kg) compared to only 2 pounds (0.9 kg) in the placebo group.

Metformin may be less effective for weight loss in normal weight or lean individuals. In one study, normal weight men given metformin for 4 months only lost 1.3 pounds (0.6 kg) on average.

Metformin for Weight Loss With Lifestyle Interventions

Metformin alone leads to modest weight loss in most people. However, combining metformin with diet, exercise or other weight loss interventions may lead to greater weight loss.

In one study, obese people were randomized to take metformin or placebo along with following a low-calorie diet for 4 months. The metformin group lost around 13% of their body weight compared to 8.5% in the placebo group.

Another trial compared metformin alone to metformin plus diet and exercise. After 4 months, the diet and exercise group lost 4 times as much weight as the metformin alone group.

The evidence clearly shows that combining metformin with lifestyle changes like diet and exercise leads to much more weight loss than metformin alone.

Is Metformin Effective for Weight Loss in the Long Term?

Most clinical trials have only looked at metformin for weight loss over periods of 36 months. However, some evidence suggests metformin may help with long-term weight maintenance.

One observational study that analyzed data from 28,000 metformin users found weight loss of approximately 9 lbs (about 4 kg) after one year and 16 lbs (7 kg) after two years.

Another large observational study found that people continued losing a small amount of weight on metformin even after being on it for 45 years.

Two clinical trials also showed those given metformin maintained more weight loss after stopping the drug compared to those given placebo.

Overall, metformin seems to promote mild but sustained weight loss over long time periods for many people. However, more high quality, long-term trials are still needed.

Does Metformin Cause Weight Gain?

While metformin often leads to weight loss, it does not cause weight gain. However, when people stop taking metformin weight gain can occur.

In clinical trials, those who were given metformin tended to lose a bit of weight, or at least not gain weight. On the other hand, those given placebo often gained a small amount of weight.

This suggests the weight gain some associate with metformin may simply reflect the natural weight gain expected for many people. In other words, metformin prevents weight gain compared to placebo, it doesnt cause weight gain.

However, some weight gain after stopping metformin therapy is common. In one study looking at long-term use, people lost 5 lbs (2.4 kg) after one year on metformin, but gained back half the weight in the year after stopping.

If metformin is working to help maintain weight, stopping it could certainly lead to weight gain. But the evidence indicates metformin does not directly cause weight gain.

Side Effects of Metformin

Metformin is generally well tolerated, with few side effects. The most common side effects are:

• Diarrhea
• Nausea and vomiting
• Gas and bloating
• Loss of appetite
• Metallic taste in mouth

Starting metformin at a low dose and slowly increasing it decreases side effects. Taking the extended-release form with a meal also helps. Side effects often go away completely after using metformin for a few weeks.

Rare but serious side effects include lactic acidosis. This only occurs in people with impaired kidney function because metformin is cleared by the kidneys. Your kidney function should be monitored before starting metformin.

Is Metformin Safe?

Metformin has been used safely for decades and is one of the most prescribed medications worldwide. Compared to other diabetes drugs, it has fewer interactions or side effects.

However, metformin is not for everyone. Those with kidney impairment, liver disease, or congestive heart failure may not be able to use metformin safely.

Metformin should never be taken by someone with a severely reduced kidney function. Your doctor will check your kidney function before prescribing metformin.

Rare side effects like lactic acidosis are also more likely if kidney function is impaired. But with proper kidney function monitoring, metformin has an excellent safety profile.

Who Should Take Metformin for Weight Loss?

Metformin is likely a good choice for weight loss in many people, including:

• People who have obesity or are overweight
• Those with insulin resistance, prediabetes or metabolic syndrome
• People with polycystic ovarian syndrome (PCOS)
• Those taking antipsychotic medications like olanzapine that causes weight gain

However, metformin is probably not useful for weight loss in lean or normal weight individuals. The evidence also shows metformin works best when combined with lifestyle changes like diet and exercise.

Of course, metformin has not been approved for weight loss by the FDA. So while doctors may prescribe it off-label, health insurance likely wont cover it for this purpose. The out-of-pocket cost may be prohibitive for some.

Should You Take Metformin for Weight Loss?

Metformin can promote mild but sustained weight loss, especially for those who are obese or overweight. It may work through mild calorie restriction, changes in metabolism, and by altering gut bacteria.

However, metformin works best when combined with changes in diet, exercise, and other lifestyle factors. Taking the drug alone results in only modest weight loss for most people.

If you have obesity, prediabetes or insulin resistance, metformin is likely a safe and potentially effective addition to diet and exercise. But it should be used under medical supervision.

For those who are lean or normal weight, evidence does not support metformin for weight loss. And due to lack of FDA approval for this purpose, youll likely need to pay for it out of pocket.

Overall, metformin can support healthy weight loss in many people. But it works best combined with diet, exercise and other lifestyle interventions.

Disclaimer: This article is for informational purposes only and does not constitute medical advice. Always consult with a healthcare professional before starting any new treatment regimen.