How long does it take metformin to work for weight loss?

If you’ve been trying to lose weight but haven’t seen the desired results, you might be looking for extra support, such as that offered by medications. Enter metformin, an oral diabetes drug that can be prescribed off-label for weight loss. But, let’s be clear, it’s not necessarily a magic bullet. So, how long does it take metformin to work for weight loss?

While the timeline varies, it can take several months to a year for metformin to work for weight loss. Read on to learn more about how metformin works, how long it takes to work for weight loss, and how much weight you might expect to lose while taking it.

The exact timeline varies between individuals, and research results are mixed. That said, studies suggest that taking metformin can lead to slight weight loss, ranging from 2 to 8 pounds over 1 to 4 years. 

Several studies have explored how metformin affects weight at different doses. One analysis of multiple studies showed that higher doses of metformin led to a larger drop in body mass index (BMI), with an average decrease of about 1 unit. For lower doses, BMI dropped by about 0.9 units. Dosages over 1,500 mg per day were most effective, especially in patients with a starting BMI over 35. This analysis also looked at how long people were treated with metformin and how it affected their weight. The biggest drop in BMI happened after six months of treatment, with an average decrease of about 1.1 units.  By the 12-month mark, however, many people had regained the weight they lost.

Other studies have seen short-term results as well, averaging 7–8 pounds of weight loss over 4–7 months. However, not all studies show significant weight loss, with some finding little to no change in weight over the long term. 

It’s important to note that many of these studies were small and only involved people with diabetes, which limits how broadly the results can be applied to the general population. 

The Diabetes Prevention Study is a large, more recent study that aimed to see metformin’s effects on participants at risk for developing type 2 diabetes. After 1–2 years on metformin, participants lost an average of 4–5 pounds with a 2.1–2.2 cm reduction in waist size. The researchers also observed that people who lost weight were more likely to be adherent, meaning they took their metformin consistently as prescribed.

The timing and amount of weight loss may also depend on consistency with lifestyle factors like diet and exercise. Conflicting studies show a wide range of weight loss timelines, and the same is true in real life. Weight loss while taking metformin depends on your health, lifestyle, and habits. Overall, metformin may lead to slight weight loss over a few months, but results are not guaranteed and tend to be gradual. 

How does metformin work for weight loss, exactly?

Metformin is thought to help with weight loss by affecting peptide hormones that control hunger and digestion, such as glucagon-like peptide 1 (GLP-1). It can slow how quickly the stomach empties, making you feel fuller for longer, which is similar to the underlying mechanism of GLP-1 agonist medications, such as Wegovy (semaglutide), though not exactly the same. Metformin may also reduce how much sugar your body absorbs from food, which can lead to fewer calories being stored.

Additionally, metformin can improve insulin sensitivity, i.e. how well your body uses insulin to lower blood sugar. By improving insulin sensitivity, metformin can help your body use insulin more effectively, which can reduce fat storage and support weight loss.

Metformin may also suppress appetite by affecting the digestive system. But in doing so, it can cause side effects such as nausea, diarrhea, bloating, and discomfort—especially when starting treatment or after dose increases. Some people are more likely to have these side effects due to genetic differences that make them absorb more metformin in their intestines. Another side effect of the medication is a metallic or bitter taste, which could also help reduce appetite. It’s unclear if these side effects are linked to how well metformin works for weight loss, though some studies show that people who stick with the medication are more likely to lose weight. 

Weight loss on metformin tends to be gradual and modest, often taking several months to show noticeable results. The timeline to see a change in your weight can vary from person to person, depending on factors such as consistency with the medication, overall health, and lifestyle habits.

When it comes to managing blood sugar, metformin begins to lower blood sugar levels within a few hours of taking it. But it may take about a week or more of consistent use to see noticeable improvements when checking your blood sugar levels. Most people taking metformin for type 2 diabetes see significant improvements in blood sugar control via a hemoglobin A1C test, which is a measurement that reflects your average blood sugar over three months. So, if you’ve heard about metformin working fast, it’s likely in the context of helping with diabetes, not weight loss.

While there’s no way to speed up how fast metformin works, there are things you can do to help boost your overall weight loss efforts. A key step is taking metformin consistently and exactly as prescribed since people who take their medication regularly tend to see better results.

Lifestyle changes, such as adjusting your diet and increasing physical activity, are also crucial for weight loss. Evidence suggests that weight changes with metformin are more likely to be linked to reducing how much you eat rather than by helping you burn more calories during exercise. Focusing on healthy, balanced meals that include fruits, vegetables, and lean proteins while reducing high-fat and processed foods can make a big difference in maintaining weight loss. Reducing daily calorie intake by about 500–750 calories can also help support gradual weight loss.

Incorporating regular physical activity, like moderate aerobic exercise, into your routine can further support your efforts. Aim for at least 150 minutes of moderate exercise each week, such as walking, cycling, or swimming. If that feels overwhelming, start small and build up over time. Even small changes in your daily habits can add up.

While it’s tempting to want quick results, combining metformin with healthy habits is the most effective way to see lasting changes.

If you’ve been taking metformin for a while—think: several months to a year—but aren’t seeing results, it might mean that metformin alone isn’t enough to achieve your weight loss goals. Other than not shedding pounds, here are some signs metformin may not be working for weight loss:

• No improvement in other health markers: If you’re not seeing changes in waist circumference or energy levels, this could be another sign that metformin isn’t making much of a difference in your body’s metabolism.

• No changes in appetite: Some people feel less hungry while taking metformin, possibly due to side effects like nausea or bitter taste. But if you don’t have appetite changes, you may want to ask your healthcare provider about other options to help you lose weight.

If you’re not making progress towards your health goals weight loss goals, it’s important to talk to your healthcare provider. They may adjust your dosage, suggest lifestyle changes like a new diet or exercise routine, or prescribe other medications. Since metformin tends to result in only modest weight loss, your healthcare provider can help you find the best approach for your goals.

Though not approved by the US Food and Drug Administration (FDA) for weight loss, metformin is commonly prescribed for controlling high blood sugar in people with type 2 diabetes. If your healthcare provider recommends metformin for weight loss, the dosage will likely be similar to the metformin dosage for diabetes. 

Metformin is usually taken in doses ranging from 500 mg to 2,550 mg per day, starting with a low dose for the first few days or week of treatment. Starting low (typically 500–850 mg once daily) and increasing the dose slowly (working up to two or three doses per day) can help minimize common side effects of metformin, such as diarrhea and stomach pain. 

Metformin—also known by several brand names such as Glucophage, Fortamet, and Glumetza—is available as an oral liquid and immediate-release and extended-release tablets. It’s best to take it with food to help minimize stomach upset and swallow the tablets whole with plenty of water. Be sure to follow your prescriber’s instructions and medical advice.

Research shows that metformin might work for weight loss whether or not you have diabetes. One study compared weight loss in two groups: one group without diabetes and one group of people with either prediabetes or type 2 diabetes. After six months, both groups lost about 6.5% of their body weight, and after one year, the non-diabetic group lost 7.4%, which was similar to the diabetic/prediabetic group’s 7.3%. 

Another study shows that people taking metformin who don’t have diabetes but are at risk for it experience weight loss of around 6–7 pounds over several months to a year. At the two-year mark, over 25% of people taking metformin had lost at least 5% of their initial weight. However, results vary. Some may see slightly more weight loss, while others may see minimal changes.

A healthcare provider can help determine if metformin is safe and appropriate for you. Be sure to tell them about any medical conditions you have as well as any over-the-counter medications, supplements, and prescription drugs you take. 

Overall, metformin is not considered a top choice for weight loss for non-diabetics, according to experts like the Endocrine Society, whose recommendations are based on years of clinical experience and peer-reviewed research. Still, metformin may offer slight weight reduction as an added benefit while taking it to manage type 2 diabetes, prediabetes, or other conditions, such as polycystic ovary syndrome (PCOS).

While metformin isn’t FDA-approved for weight loss, it may offer some benefits for people who are trying to lose weight. However, results tend to be modest and gradual. For the best outcomes, it's important to combine metformin with healthy habits like a balanced diet and regular exercise. 

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How we reviewed this article

Every article on Health Guide goes through rigorous fact-checking by our team of medical reviewers. Our reviewers are trained medical professionals who ensure each article contains the most up-to-date information, and that medical details have been correctly interpreted by the writer.

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Current version

October 31, 2024

Written by

Patricia Weiser, PharmD

Fact checked by

Beverly Tchang, MD and Raagini Yedidi, MD

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About the medical reviewers

Beverly Tchang, MD

Beverly Tchang, MD, is an Obesity Medicine Advisor for Ro. She is also an assistant professor of Clinical Medicine at Weill Cornell Medicine in New York and triple board-certified in Internal Medicine, Endocrinology, and Obesity Medicine.

Raagini Yedidi, MD

Raagini Yedidi, MD, is an internal medicine resident and medical reviewer for Ro.