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Why did my doctor prescribe metformin for weight loss?

Metformin is a medication that was originally developed to treat type 2 diabetes. However, over the years doctors have found that metformin can also aid in weight loss for some people. If your doctor has prescribed metformin to help you lose weight, it’s because they believe the benefits outweigh any potential risks.

How does metformin aid in weight loss?

The exact mechanisms behind how metformin contributes to weight loss are not fully understood. However, there are a few key ways that metformin is believed to help:

  • Improves insulin sensitivity – Metformin makes the body more sensitive to insulin. This allows the body to metabolize sugar more effectively and prevent spikes in blood sugar after meals.
  • Lowers glucose production – Metformin reduces the amount of glucose produced by the liver. Excess glucose can be converted into fat, so reducing glucose production can aid weight loss.
  • Suppresses appetite – Some studies have shown metformin can blunt appetite and reduce food intake, particularly of carbohydrates. This can lead to eating fewer calories.
  • Alterations in gut bacteria – Metformin seems to favorably change the balance of gut microbes which are tied to weight regulation.

Together, these metformin mechanisms can make it slightly easier to lose weight through diet, exercise, and other lifestyle measures.

What types of patients may benefit from metformin for weight loss?

Doctors are most likely to prescribe metformin for weight loss in patients that fit the following criteria:

  • Overweight or obese
  • Prediabetes or insulin resistance
  • Type 2 diabetes
  • Polycystic ovary syndrome (PCOS)

Patients that fall into these categories tend to struggle with insulin sensitivity and glucose metabolism. Therefore, they are more likely to benefit from the mechanisms of metformin described above.

Overweight or obese

Being overweight or obese is tied to underlying issues with metabolism and insulin function. Metformin can help counteract these issues. One study found obese patients without diabetes who took metformin lost 5-10 pounds more over 1 year compared to placebo.

Prediabetes/insulin resistance

Prediabetes and insulin resistance are conditions where the body has trouble effectively using insulin. This results in elevated blood sugar. Metformin directly targets insulin sensitivity, making it a good option for those with prediabetes or insulin resistance.

Type 2 diabetes

Metformin is one of the most common medications prescribed for type 2 diabetes. Improving blood sugar control in diabetics can remove excess sugar as a source of calories and jumpstart weight loss.


Many women with polycystic ovary syndrome (PCOS) have insulin resistance. Metformin helps lower insulin levels, which can relieve PCOS symptoms and spur weight loss in overweight women with PCOS.

What results can be expected from metformin for weight loss?

On average, metformin alone (without lifestyle changes) can lead to 3-5 lbs of weight loss over 3-6 months. This modest amount of weight loss can be helpful for those struggling to shed pounds through diet and exercise alone.

Some research has found metformin may help people lose up to 10% of their body weight when combined with diet and exercise. For a 200 pound person, that would equate to 20 pounds of weight loss.

However, others lose very little weight on metformin. Response varies from person to person.

Factors that influence weight loss results

Several factors impact how much weight a person might lose on metformin:

  • Dosage – Higher metformin doses are linked to more weight loss, but also increased side effects.
  • Diet – Metformin works best alongside a healthy reduced-calorie diet for weight management.
  • Exercise – Being active while taking metformin enhances weight loss results.
  • Other medications – Taking other diabetes or weight loss meds with metformin can improve results.
  • Genetics – Some people’s bodies respond better to metformin’s effects than others.

As a general guideline, the more lifestyle changes someone makes while on metformin, the more weight they are likely to lose.

Is metformin effective for weight loss in non-diabetics?

Most research on using metformin for weight loss has focused on those with obesity, prediabetes or diabetes. But some studies have also shown modest weight loss in non-diabetic individuals.

In one study of obese people following the same diet and exercise plan, those taking metformin lost around 5-6% of their body weight, while the placebo group lost only 2-3%.

Another study of adolescents with obesity but no diabetes found metformin caused significantly greater weight and fat loss compared to placebo.

While more research is still needed, these studies suggest non-diabetics may also benefit from metformin’s weight lowering effects.

Should metformin be used for weight loss in healthy individuals?

In general, most experts do not recommend metformin solely for weight loss in healthy individuals with a normal BMI and no insulin issues. Some reasons why include:

  • Modest effects – Weight loss from metformin alone is typically moderate without diet and exercise.
  • Unwanted side effects – Metformin can cause GI side effects like diarrhea and nausea, especially when first starting.
  • Low nutritional impact – Metformin does not prevent fat or calorie intake like some obesity medications.
  • Long-term safety unclear – Metformin has a good safety profile, but less data exists for very long term use in non-diabetics.

Lifestyle interventions should be the first line treatment for healthy weight loss. However, those struggling with excess weight related to insulin resistance issues may benefit from metformin.

What lifestyle changes should be made when taking metformin for weight loss?

To maximize the effectiveness of metformin for weight loss, doctors recommend combining it with lifestyle modifications. Some recommended changes include:

Follow a weight loss diet

Metformin is not a magic diet pill. A reduced calorie diet supporting a modest 1-2 pound per week weight loss should be followed. Lower carb diets may work well with metformin’s mechanisms.

Increase physical activity

Exercise is a key aspect of weight management. Aim for 150-300 minutes of moderate activity like brisk walking or cycling per week while taking metformin.

Improve sleep habits

Getting enough quality sleep supports weight control and insulin function. Adults should aim for 7-9 hours of sleep each night.

Reduce stress

Chronic stress prompts the body to hold on to excess fat. Relaxation techniques like yoga, meditation and mindfulness can support weight loss.

See a dietitian

Consulting with a registered dietitian skilled in medical nutrition therapy can help optimize the diet and establish healthy eating habits.

Making diet, exercise, and other supportive lifestyle changes greatly increase the likelihood of achieving weight loss success with metformin.

What are the side effects of metformin for weight loss?

Metformin is generally well tolerated, but some side effects can occur. Potential side effects include:

  • Digestive issues – Stomach pain, diarrhea and nausea are common metformin side effects. Starting at a low dose and taking with food can help minimize GI issues.
  • Metallic taste – Some report a bothersome metallic or bitter taste in the mouth while on metformin.
  • Low vitamin B12 – Metformin may lower vitamin B12 levels over time. Supplementation may be recommended.
  • Headaches – Headache is an occasional side effect of metformin.
  • Fatigue – A small number of metformin users experience unusual tiredness or weakness.

Rare but serious side effects include lactic acidosis and kidney problems. Extended-release metformin is less likely to cause GI side effects compared to regular metformin.

Table comparing metformin side effects

Side effect Estimated frequency
Diarrhea 10-20%
Nausea 5-10%
Vomiting 3-5%
Gas or bloating 5-10%
Indigestion 5-10%
Headaches 2-5%
Metallic taste 1-5%

Gastrointestinal side effects like diarrhea are most common when first starting metformin, but typically improve over time.

How long does it take for metformin to help with weight loss?

Most people do not see dramatic weight loss from metformin alone in the first few weeks. Noticeable fat loss results can take 3-6 months.

Metformin immediate-release tablets reach maximum blood concentrations in about 2 hours. It takes approximately 24-48 hours for most of the metformin to be eliminated from the body.

So metformin starts working right away to lower blood sugar and insulin levels after the first couple doses. However, its effects on metabolism, body weight, and gut bacteria likely take longer to fully manifest.

Continued use over weeks and months allows metformin’s cumulative effects on insulin function, appetite, glucose production, and other physiological factors to accrue. This eventually tips the body into better fat burning mode and weight loss.

Timeline of expected metformin weight loss results

  • First 1-2 weeks – Little to no weight loss noticeable yet.
  • 1 month – 1-3 pounds lost on average.
  • 2 months – 2-6 pounds lost on average.
  • 3 months – 4-8 pounds lost on average.
  • 6 months – 7-12 pounds lost on average.

Following a healthy diet and increasing physical activity while taking metformin will help boost weight loss results over this timeline.

Does metformin help with weight loss by itself?

Metformin can aid weight loss to a modest degree by itself, without any additional efforts. On average, just taking metformin regularly can result in losing about 3-5 pounds over 3-6 months.

One study found obese individuals who only took metformin lost on average 5-6 pounds over 6 months. The placebo group gained about 1 pound on average.

Another study showed metformin caused mild 1.5-2.5 pound weight loss in patients with prediabetes over 9 months without any lifestyle changes.

However, to achieve greater amounts of weight loss like 10% of body weight or more, metformin really works best when combined with dietary changes, more activity, and other healthy habits.

Should I take metformin for weight loss?

Metformin can be a helpful adjunct treatment for weight management in some individuals with obesity, prediabetes or diabetes. However, metformin shouldn’t replace proper nutrition, physical activity, and other lifestyle measures aimed at weight loss.

Before taking metformin for weight loss, consider whether:

  • You have insulin resistance issues like prediabetes, which metformin directly addresses.
  • You are willing to alter your diet and exercise habits to enhance metformin effects.
  • More intensive weight loss approaches like bariatric surgery may be an option for you.
  • You are okay with metformin’s potential GI side effects.
  • You’ve discussed the pros and cons with your doctor.

Metformin can give your weight loss efforts a helpful boost. But non-medication based interventions should serve as the foundation of any weight management approach.


Metformin is primarily a medication used for blood sugar control in type 2 diabetes. But it also appears to aid in weight loss for some individuals with obesity or prediabetes.

When paired with diet, exercise, and other healthy lifestyle changes, metformin can help accelerate fat loss. On average, it may result in 5-10 pounds lost over 6 months.

However, metformin is not a miracle weight loss drug. Mild GI side effects are common, and not everyone responds the same. Working closely with your doctor is important to see if metformin makes sense for you as part of a comprehensive weight management plan.