Metformin Weight Loss: Causes and Side Effects

By Craig Sorkin, DNP, APN
Medically reviewed checkmarkMedically reviewed
July 12, 2022

Metformin is a medication used to treat type 2 diabetes mellitus.

It may also be used for polycystic ovary syndrome (PCOS), insulin resistance, and prediabetes.

While metformin is not a weight-loss drug, because of how it affects glucose and insulin in the body, it may help people with blood sugar problems lose weight.

In this article, we’ll look at research on how metformin causes weight loss, side effects, and possible drug interactions.

Does Metformin Help With Weight Loss?

Research does not have a clear answer as to why metformin may cause weight loss.

It is most likely due to several different effects of the drug:

  • Reduced hunger: Metformin plays a role in hunger cues. Research notes that people who take metformin have lower hunger levels. The drug does not suppress the appetite but instead changes the part of the brain that regulates appetite desire. Metformin may lead people to eat less at each meal, which may help them lose weight.
  • Side effects of the drug: Metformin may cause nausea and diarrhea. Initially as a person is adjusting to the medication, the combination of an upset stomach, eating less, and having diarrhea may cause a temporary drop in weight. 
  • Better insulin and glucose balance: Since metformin improves sensitivity to insulin and reduces how much glucose circulates in the blood, it may decrease how much excess glucose is stored as fat. Over time, this could result in weight loss.
  • Gut health: Research shows that people living with obesity may have fewer short-chain fatty acids in the gut. These acids have a protective effect on many aspects of health, including weight. Metformin increases the production of short-chain fatty acids, which may contribute to weight loss.

Some research shows that metformin doesn’t affect weight beyond dietary and lifestyle changes that are likely made by people taking metformin.

Other research finds significant weight decreases in people who were obese, independent of lifestyle factors. Multiple studies report that metformin paired with a low-calorie diet reduces visceral body fat.

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Is metformin an effective weight-loss pill?

Metformin is not a weight-loss medication. It isn’t prescribed for people who simply want to lose weight.

Some researchers consider insulin resistance to be an important prerequisite for using metformin, while others may not prescribe it outside of type 2 diabetes or PCOS.

When metformin is indicated for health conditions, it may lead to weight loss as a side effect.

Can People Without Diabetes Take Metformin?

Some healthcare providers prescribe metformin to support weight loss in people who are obese and have other contributing factors such as insulin resistance.

Even without diagnosed type 2 diabetes or the signs of prediabetes, metformin may work to support weight loss when insulin may not be as effective in the body.

Not all obesity is associated with insulin-related problems, though.

Even if a medical provider prescribes metformin for weight loss, it will not do the job on its own.

Healthy lifestyle behaviors such as the below are needed to promote weight loss with metformin:

  • Exercising for 30 minutes a day, five days per week
  • Avoiding sugary beverages
  • Drinking enough water
  • Eating a balanced diet that’s rich in unprocessed foods

Precaution and Risks

Metformin carries a black box warning, the FDA’s strictest label.

In rare cases, metformin can cause lactic acidosis.

This condition occurs when too much metformin builds up in the body.

Lactic acidosis is a medical emergency and is potentially fatal if left untreated.

Symptoms include flushing (sudden reddening), feelings of warmth on the skin, lightheadedness, dizziness, nausea, vomiting, heart rate changes, and muscle pain.

Metformin can also cause unsafe complications or interactions with the following health conditions:

  • Kidney problems or disorders
  • Metabolic acidosis
  • Heart failure
  • Before surgical procedures
  • Before radiology procedures with iodine contrast

Metformin side effects

The common side effects of metformin are typically short-term while the body adjusts to the medication and include:

Over time, metformin may contribute to vitamin B12 deficiency or anemia.

Metformin drug interactions

There are many possible drug interactions with metformin.

Keep your medical provider and pharmacist informed about the prescriptions, OTC medicines, and supplements that you take.

Metformin can interact with the following:

  • Cimetidine
  • Digoxin
  • Oral contraceptives
  • Corticosteroids
  • Quinidine
  • Ranitidine
  • Dofetilide
  • Morphine
  • Vancomycin
  • Phenytoin
  • Beta blockers
  • Procainamide
  • Triamterene
  • Calcium channel blockers
  • Coenzyme Q10
  • Garlic
  • Diuretics
  • Estrogens
  • Green tea
  • Phenothiazines
  • Chromium
  • Sympathomimetics
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When to See a Medical Provider

If you are trying to lose weight and feel that your efforts aren’t making enough progress, speak to a healthcare provider.

They can recommend potential medications or other support that could help.

While metformin is not a weight-loss drug, it may be effective to help some people lose weight.

A medical provider can determine if metformin may be appropriate for you.

How K Health Can Help

Did you know you can get affordable primary care with the K Health app? Download K to check your symptoms, explore conditions and treatments, and if needed text with a healthcare provider in minutes.

K Health’s AI-powered app is HIPAA compliant and based on 20 years of clinical data.

Frequently Asked Questions

Can a non diabetic take metformin for weight loss?
While it is not a weight-loss drug, research has shown that metformin can support dietary and lifestyle efforts to lose weight. Therefore, medical providers may prescribe metformin for insulin resistance or weight loss if they determine it’s appropriate for the patient.
Why does metformin make you lose weight?
It’s unclear exactly why metformin may cause weight loss. It may decrease appetite and change the gut microbiome in a way that is more supportive of weight loss. It can also balance insulin and glucose, which can contribute to weight loss over time.
Does metformin reduce stomach fat?
Metformin is not a weight-loss drug, but some research suggests it may support the loss of visceral fat, the dangerous type of fat found in the abdomen.
K Health articles are all written and reviewed by MDs, PhDs, NPs, or PharmDs and are for informational purposes only. This information does not constitute and should not be relied on for professional medical advice. Always talk to your doctor about the risks and benefits of any treatment.

K Health has strict sourcing guidelines and relies on peer-reviewed studies, academic research institutions, and medical associations. We avoid using tertiary references.

Craig Sorkin, DNP, APN

Craig Sorkin, DNP, APN is a board certified Family Nurse Practitioner with over 15 years experience. He received his Undergraduate and Graduate degrees from William Paterson University and his doctoral degree from Drexel University. He has spent his career working in the Emergency Room and Primary Care. The last 6 years of his career have been dedicated to the field of digital medicine. He has created departments geared towards this specialized practice as well as written blogs and a book about the topic.

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