Is Weight Loss a Side Effect of Metformin?

Medically reviewed by Mary Choy, PharmD

Metformin is commonly prescribed for managing blood sugar levels in individuals with type 2 diabetes.

Some people may experience weight loss as a side effect of taking metformin. There are a few reasons why metformin may contribute to weight loss, including its role in decreasing appetite and changing gut bacteria. Metformin is also known to cause gastrointestinal-related side effects, such as diarrhea and nausea, which may affect how much you can eat.

However, metformin is not specifically intended or approved for weight loss purposes.

This article will discuss why you might experience weight changes on metformin and whether this means metformin could be used as a potential weight loss drug.

How Metformin Works

Metformin belongs to a class of drugs called biguanides. It is used to help manage type 2 diabetes by lowering blood sugar levels.

In type 2 diabetes, insulin is produced in the body, but the cells are not able to respond to the insulin being released. This is known as insulin resistance.

As a result, your cells cannot absorb sugar, so it remains in your blood and causes high blood sugar levels. Metformin can prevent high blood sugar levels in three ways:

• It decreases sugar production in the liver.

• It lowers the absorption of sugar from the food we eat.

• It makes your body more sensitive to insulin.

Weight Loss As a Side Effect of Metformin

It is clinically shown that a common side effect of metformin is weight loss.

Studies have suggested that metformin decreases appetite and changes the bacterial community of the gut.

Metformin decreases appetite by reducing levels of a hormone called leptin. Leptin regulates appetite by telling your brain when your stomach is full. With reduced sensitivity to leptin, you don’t feel as hungry anymore.

Another way metformin can make you lose weight is by changing the bacteria in your gut. There are certain bacteria in our stomachs that break down short-chain fatty acids. The breakdown of short-chain fatty acids gives our body energy and helps regulate sugar levels. After metformin treatment, the bacteria responsible for fatty acid metabolism increase, leading to weight loss.

Metformin may also cause some digestive-related side effects, such as diarrhea or nausea, which can affect appetite and food intake.

Other Potential Causes of Weight Loss

If you are losing weight while taking metformin, it may or may not be caused by the medication itself. Other factors can contribute to weight loss, such as changes in diet, digestive issues, or other medications.

Lifestyle Changes

If you take metformin, that means you are likely also making lifestyle changes to help manage your diabetes.

According to the American Diabetes Association, managing type 2 diabetes is best achieved by practicing 150 minutes per week of moderate-intensity exercise, such as brisk walking, and starting a sugar- or carb-free diet. Increased physical activity and diet changes are associated with decreased body weight.

Digestive Issues

Digestive issues can also be the reason why you are losing weight. These symptoms or diseases may affect appetite and food intake, potentially leading to weight loss in some individuals. Some digestive problems that are related to weight loss include:

• Diarrhea

• Vomiting

• Stomach infection or virus

• Inflammatory bowel syndrome (IBS)

Other Medications

Other medications can also cause weight loss as a side effect. For example, levothyroxine rebalances your hormones to break down food for energy, which may lead to modest weight loss.

Other medications that can cause weight loss include stimulants for attention deficit hyperactivity disorder (ADHD), such as Adderall and Concerta.

Could Metformin Be Used for Weight Loss?

Although metformin can provide modest weight reductions, it is not approved by the U.S. Food and Drug Administration (FDA) as a weight loss medication.

Some studies have demonstrated metformin's potential effects on body weight. However, based on clinical studies, the amount of weight lost on metformin varies.

Based on one six-month study, people with diabetes taking metformin only decreased their weight by 5%. One review of studies found that, on average, metformin in adults over 60 resulted in about 4 pounds of weight loss compared with a placebo.

Another study assessed metformin's effect on weight in 154 individuals with obesity who did not have diabetes. Over six months, those who took metformin lost around 12 to 15 pounds, on average.

In one long-term study, 28.5% of people taking metformin lost about 5% or less of their body weight after one year. However, those who lost weight on metformin had the greatest success maintaining weight loss six to 15 years after.

Additionally, there are other medications available, like Wegovy (semaglutide), that are specifically approved to help manage weight. Semaglutide has shown total body weight loss percentages of up to 11% after six months of use.

Taking any medication that can help you lose weight is not the best practice to maintain a healthy lifestyle. Therefore, it is important to consider a healthy diet and exercise plan, even if you are on a treatment for obesity.

Can You Take Metformin If You Don’t Have Diabetes?

If you do not have pre-diabetes or diabetes, your healthcare provider will most likely not prescribe metformin to help you lose weight.

One possible case a healthcare provider might consider metformin for weight loss is for people without diabetes who are on medications for schizophrenia.

This is because antipsychotic medications, such as clozapine and olanzapine, have a high risk of weight gain. Based on a collection of studies, metformin effectively decreased body weight in people without diabetes who have gained weight while being treated for schizophrenia.

When to See a Healthcare Provider

Engaging in open and regular communication with a healthcare provider is crucial for anyone concerned about maintaining a healthy weight, regardless of whether one is worried about excessive weight loss or dealing with obesity.

Your healthcare provider can provide personalized guidance, evaluate health risks, ensure a balanced approach, monitor progress, and offer valuable support throughout the journey toward achieving and sustaining a healthy weight.

You may also want to consider speaking to a registered dietitian and nutrition (RDN), who can help establish healthy eating practices.

Summary

While metformin has been commonly associated with weight loss, the medication is not intended to be used for weight loss purposes.

There are a few possibilities for why metformin helps you lose weight, including loss of appetite and a change of good bacteria in your stomach. Other factors other than metformin may contribute to weight loss, such as changes in diet and exercise, digestive issues, or other medications.

If you feel that you may need medication to help you achieve a healthy weight, contact your healthcare provider to discuss a personalized weight management plan.

Frequently Asked Questions

How much weight loss does metformin cause?

How much weight one loses on metformin can vary. In one study, people who took metformin for six months lost 5% of their body weight. This means that, for example, someone who weighs 180 pounds would have lost 9 lbs over six months.

Can metformin be prescribed off-label for weight loss?

Yes, metformin has been used off-label to help manage weight gain related to antipsychotic medications, such as risperidone and clozapine.

Who shouldn’t take metformin?

You should not take metformin if you are searching for a medication that has drastic results in weight loss. Metformin may only offer modest weight reduction. Other available treatments approved by the FDA specifically for weight loss are more effective options.

In addition, you should avoid taking metformin if you have kidney disease or kidney failure.

Acknowledgement

The author would like to recognize and thank Alexya Rosas for contributing to this article.