Metformin dosage guide: Taking metformin for weight loss

Metformin is a prescription drug that was approved by the U.S. Food and Drug Administration (FDA) in 1994 as a treatment for type 2 diabetes. Also known as metformin hydrochloride, it improves blood sugar levels by causing the liver to release less glucose and improving insulin sensitivity. 

Formulated as an oral tablet with dose strengths typically ranging from 500 to 2,550 mg, it’s available as immediate-release tablets, usually taken twice a day, or as extended-release tablets, which can be taken once daily. 

It’s sold in several FDA-approved generic forms and under the brand names Glumetza® and Fortamet®. (Note: Glucophage® and Riomet® have been discontinued in the U.S.)

How does metformin support weight loss? 

The exact way in which metformin helps weight loss isn’t fully understood. Still, various studies have shown that metformin can affect weight. Generally, it’s considered  a “weight-neutral” medication, meaning it doesn’t cause significant weight loss or gain. 

However, in a Diabetes Prevention Program study published in the Annals of Internal Medicine, for participants who lost at least 5% of body weight, metformin was the most effective method of weight maintenance six to 15 years after the initial weight loss compared to lifestyle interventions or placebo. In that study, the dosage of metformin was 850 mg, taken twice a day. 

Another reason health care providers may prescribe metformin off-label for weight loss is for people who have gained weight as a side effect of taking antipsychotic medications. 

Personalized medical advice from an obesity medicine specialist can help you determine whether metformin could effectively support your weight loss goals.

While you take metformin for weight loss, you may want to avoid certain foods and minimize alcohol to support your goals. 

What is the standard dosage for metformin? 

Standard dosing for metformin depends on the reason it’s prescribed. 

Patients usually start at a low dose, which is gradually increased to reduce the common side effects of metformin, including stomach pain, diarrhea, nausea, vomiting, and decreased vitamin B12 levels. More serious side effects can also occur. 

The FDA also has a “black box warning” on metformin as it carries a serious safety risk of lactic acidosis. This rare but potentially fatal condition is when too much lactic acid builds up in the blood. It can lead to low blood pressure, trouble breathing, heart failure, and even death.

Additionally, metformin may stimulate ovulation in those with polycystic ovary syndrome (PCOS) or who are premenopausal, which may increase the risk of unintended pregnancy. If you’re in a sexual relationship that can result in pregnancy, use at least one form of birth control while taking metformin unless you’re planning on getting pregnant. Find detailed side effect and risk information on our dedicated metformin page. 

‍Metformin dosage for type 2 diabetes

The most common reason for taking metformin is to treat type 2 diabetes mellitus and control hyperglycemia. When taken for this purpose, metformin (immediate release) is started at a standard initial dose (typically 500 mg orally once or twice a day or 850 mg orally once daily) and then increased incrementally until blood glucose levels normalize. 

Prescribers may increase the dose by 500 mg or 850 mg each week. Most people will achieve results with a dose of 850 to 1,000 mg taken twice a day. The maximum dosage of metformin is 2,550 mg once per day.

For extended-release tablets, metformin is usually started at 500 mg or 1000 mg per day in a single dose. This dose is increased by 500 mg per week, up to a dosage of 2,000 mg once a day. 

Note: Metformin is not a treatment for type 1 diabetes. 

Metformin dosage for treating antipsychotic-induced weight gain 

When prescribed to counter weight gain from antipsychotic medications, metformin can be taken as immediate- or extended-release tablets. 

The starting dose for immediate-release tablets is 250 to 375 mg, taken two or three times per day for a total dose of 750 to 1,000 mg per day. This can be increased weekly to a maximum dosage of 2,550 mg daily. 

With extended-release tablets, the starting dosage of metformin is 500 mg daily. Your provider can increase this dose every few weeks by 500 mg to a maximum dosage of 2,000 mg daily. 

Metformin dosage for weight loss

Since metformin hasn’t been approved by the FDA for weight loss, there isn’t a standard recommended dosing for this purpose. 

That said, a meta-analysis of studies on the effectiveness of metformin for weight loss found that the typical dosing in studies was between 1,000 mg and 2,000 mg per day, with one study using the maximum dose of 2,550 mg per day. 

This analysis found that taking metformin for six months decreased participants’ body mass index (BMI) by approximately one point. 

Do any medical conditions require metformin dosage adjustments? 

Metformin is a biguanide medication that is metabolized or cleared from the body by the kidneys. Therefore, people with renal impairment (reduced kidney function) may need an adjusted dose or more frequent monitoring of kidney function. And those with advanced kidney disease should not take it. 

One way to measure kidney function is eGFR, or estimated glomerular filtration rate. Derived from a blood test, this estimates how well your kidneys are working by measuring the level of creatinine in the blood. Here are FDA-recommended metformin dosages based on kidney function: 

• If your eGFR is above 60 mL/min: Take the standard dosage of metformin, and get an eGFR test every 12 months.
• If your eGFR is 45-60 mL/min: Take the standard dosage of metformin, and get an eGFR test every 3 to 6 months. 
• If your eGFR is 30-45 mL/min: Do not start metformin. Your doctor may recommend a different treatment. If you are already taking metformin, your doctor may advise a different dosage.

What are contraindications for taking metformin? 

People with severe kidney disease (an eGFR lower than 30 mL/min); acute or chronic metabolic acidosis, including diabetic ketoacidosis; or hypersensitivity to metformin should not take metformin. 

You also shouldn’t take a metformin dose on the same day as another medication that could harm the kidneys, such as the iodine-containing contrast medium (or dye)  used in CT scans.  

What are known risks of taking metformin? 

Studies show long-term use of metformin may, in rare cases, lead to complications including pancreatitis, hepatitis, abnormal blood clotting, vitamin B12 deficiency, and reactive hypoglycemia. Additionally, metformin may stimulate ovulation in those with PCOS or who are premenopausal and may increase the risk of unintended pregnancy.

The FDA also has a “black box warning” on metformin for the serious safety risk of lactic acidosis. This rare but potentially fatal condition is when too much lactic acid builds up in the bloodstream. It can lead to low blood pressure, breathing issues, heart failure, and even death. People with liver problems, severe kidney problems, excessive alcohol consumption, and congestive heart failure are at greater risk for lactic acidosis. Find detailed side effect and risk information on our dedicated metformin page. 

What if I miss a dose of metformin—or take too much? 

If you miss a dose of metformin, take it as soon as you remember. If it’s almost time for your next dose, then just wait and take the next dose. Never take a double dose. 

Taking too much metformin may cause serious consequences like lactic acidosis or hypoglycemia. If you accidentally take too much, call the poison control helpline at 1-800-222-1222 and watch for signs of overdose. These could include low blood sugar, fatigue, weakness, vomiting and nausea, shortness of breath, dizziness and lightheadedness, slow or fast heart rate, and chills. If you experience severe symptoms, call 911.

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