How Does Metformin Help You Lose Weight?

Metformin is one of the most widely prescribed diabetes drugs. It is also gaining traction as a weight loss drug. Read on to learn how metformin works, how it may help with weight loss, and how it compares to other weight loss options.

What is metformin, and how does it work for weight loss?

Metformin belongs to a sub-class of diabetes medications known as biguanides. It’s available in several forms, both branded and generic:

• Immediate-release (IR) oral tablets
• Extended-release (XR/ER) oral tablets
• Oral IR solution

Metformin works by making your body's cells more responsive to insulin, which lowers your blood sugar levels. This is especially important if you have type 2 diabetes, because your body struggles to respond properly to insulin.

A few ways metformin works to support weight loss include:

• Lowering liver glucose: Metformin limits how much blood sugar your liver produces, especially overnight.
• Improving insulin sensitivity: It helps your body use insulin properly. This means your cells can burn more of your blood glucose for energy instead of storing it as fat.
• Changing your gut bacteria: Metformin works in your digestive tract to increase healthy gut bacteria, which can influence appetite and weight.

What are the uses of metformin for weight loss?

Metformin is sometimes prescribed for weight loss if a patient has:

• Overweight (BMI 25 to 30) or obesity (BMI equal to or greater than 30): Metformin is usually prescribed to patients with a BMI of 30 or higher (obesity), or overweight who also have a high type 2 diabetes risk, such as high fasting blood glucose.
• Insulin resistance or prediabetes: Metformin can control blood sugar and improve insulin response in patients whose type 2 diabetes risk is higher than average. Along with healthy lifestyle changes, it can slow the chance of developing type 2 diabetes.
• Polycystic ovary syndrome (PCOS): Metformin can lower insulin and androgens (steroid hormones) if you have PCOS, especially when taken with other medications. It can improve your menstrual frequency and ovulation.
• Antipsychotic-induced weight gain: Some antipsychotic medications can cause weight gain, which increases your type 2 diabetes risk. Taking metformin can slow this down or help you lose a modest amount of weight.

Is metformin for weight loss effective?

Metformin can help you lose a moderate amount of weight. However, your exact weight loss will depend on your dose, how long you take it, and why it was prescribed.

Studies show that people taking metformin lose an average of 2% to 3% of their body weight over the first 6 months. This is a much smaller amount than people usually lose with newer, FDA-approved diabetes drugs that cause weight loss. These GLP-1 drugs include Mounjaro (tirzepatide) and Ozempic (semaglutide), which can often cause weight loss of 10% to 20%.

Studies show how much weight different groups lost while taking metformin:

• Nondiabetic adults with obesity or overweight: Achieved an average reduction in total body mass index (BMI) of 2.5% in clinical trials ranging from 3 to 12 months.
• People with prediabetes or high diabetes risk: Maintained a small reduction of body weight of 2% to 3% over 2.8 years.
• Women with PCOS: Reduced their BMI by 2% to 3.5% (representing 0.5 to 1 BMI point) in clinical trials lasting at least 3 months.
• Antipsychotic-induced weight gain: Lost an average of 3% to 4% of body weight over 2.8 years.
• Children and adolescents with obesity: Lost around 2.5% to 3% of body weight over 6 months.

Research by The Diabetes Prevention Program shows that metformin works best when paired with intensive lifestyle changes. The program tracked these patients over 2.8 years. Patients who practiced intensive lifestyle changes like a healthy diet and regular exercise lost an average of 6% (12 lbs). In comparison, patients taking metformin without significant changes lost around 2% (5 lbs).

How long does it take to lose weight with metformin?

People usually see the most weight loss within the first 6 to 9 months after they start taking metformin. This change is usually gradual rather than immediate. Metformin changes how your body handles insulin and glucose, so your metabolism needs time to adjust.

• The first few weeks: You may notice your appetite decreases as your digestion adjusts to the medication. It is rare to notice weight loss this early.
• Around 6 to 9 months: This is when the most weight loss tends to occur. On average, people lose 1 BMI unit (2% to 3% of their body weight).
• Long-term: People who take metformin long-term usually maintain a stable weight rather than continue to lose weight. However, some patients can keep losing a modest amount (usually 1% to 3% of their body weight) for years.

Who should take metformin for weight loss?

Because metformin is a prescription-only medication, you should only take it if your healthcare provider has prescribed it. Metformin has not been approved by the FDA for weight loss alone.

Talk to a licensed clinician if you don’t have diabetes or one of the above conditions and want to lose weight. They can advise you on FDA-approved weight loss medications and assess whether they’re right for you.

Prescription options like glucagon-like peptide-1 (GLP-1) receptor agonists like Wegovy (semaglutide) and Saxenda (liraglutide) are specifically designed for weight reduction. A dual-action injection called Zepbound (tirzepatide) is also FDA-approved for weight loss. If prescribed, they can be a safe way to lose much more weight than metformin.

Metformin side effects: Is it safe?

Clinical trials show that metformin is safe and effective when used correctly. However, it can cause side effects, especially during the first days to weeks of starting treatment or increasing your dose. Most metformin side effects affect your digestive system.

Common side effects of metformin include:

• Diarrhea
• Bloating
• Stomach pain
• Gas
• Indigestion
• Vomiting
• Constipation
• Heartburn

More severe side effects of metformin include:

• Hypoglycemia (low blood sugar): Symptoms include a rapid heartbeat, extreme hunger, sweating, nausea, and feeling shaky.
• Lactic acidosis (lactic acid buildup in your blood): Signs include fatigue, rapid breathing, nausea, confusion, trouble with coordination, and muscle cramps.
• Vitamin B12 deficiency: Metformin lowers how much B12 your body can absorb. It can cause B12 deficiency when you use it for a longer time (4 to 5 years or longer) or take higher doses (1000 mg/day to 1500 mg/day). Early B12 deficiency symptoms include unexplained fatigue, brain fog, mood changes, a sore tongue, and nerve issues like tingling or poor balance.

Get in-person medical attention right away if you notice any of these severe metformin side effects. Metformin may not be safe for you if you have a previously diagnosed medical condition.

Your healthcare provider may not prescribe metformin if:

• You are over 65 years of age
• You have a history of heart attacks or heart disease
• You have had a stroke
• You have type 1 diabetes
• You have a history of diabetic ketoacidosis
• You have a history of liver or kidney disease
• You are pregnant, trying to conceive, or breastfeeding
• You have a known allergy to metformin hydrochloride (the active ingredient in metformin)

Tell your provider about any medical conditions or allergies you have before starting metformin. Be sure to share a full list of medications or supplements you are taking so they can give you personalized advice. Ask your provider about drinking alcohol while taking metformin. This may not be safe for certain people.

How do I get a prescription for metformin?

Book a virtual visit with a licensed medical provider on Sesame to discuss whether metformin is suitable for your goals. Appointments are available 24/7—no insurance required.

During your call, your provider can recommend a safe, effective treatment and write you a metformin Rx if appropriate. They can also recommend and prescribe alternative treatments, if suitable, and ways to save money on your medication.

Frequently asked questions

How long does it take to lose weight with metformin?

Most people see the most noticeable weight loss within 6 to 9 months of taking metformin consistently. Small appetite changes can happen within the first few weeks. Larger body weight changes usually happen gradually over the first year of treatment.

Does metformin cause weight gain?

No, metformin doesn’t cause weight gain—it is weight-neutral (no change) or causes modest weight loss. Metformin helps your body burn blood glucose for energy instead of storing it as fat.

Is metformin better than Ozempic for weight loss?

No, metformin usually causes much less weight loss than Ozempic. Studies show that people taking metformin lost an average of 2% to 3% of their body weight. People taking FDA-approved GLP-1 medications like Ozempic, Wegovy, or Mounjaro often lost around 10% to 20%.

Are there alternatives to metformin for weight loss?

Yes, there are several highly effective alternatives to metformin for weight loss, although their FDA approvals are different. These include:

• Weight loss-approved GLP-1 and dual-action medications like Wegovy and Zepbound
• Diabetes-approved GLP-1 medications like Ozempic and Mounjaro
• Weight loss-approved oral pills like Qsymia (phentermine-topiramate) and Contrave (naltrexone-bupropion)
• Lifestyle modifications, including a healthy diet and regular exercise

How Sesame can help with your weight loss journey

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Get a video consultation with a weight loss specialist of your choice and a weight loss medication Rx if appropriate, plus unlimited checkins with your provider, continued support, and more.

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