[Last updated 9th November, 2017]
Metformin is a medication said to cause weight loss, but is it true?
Should you be worried if you are underweight, or should you use it if you want a slimmer waistline?
This article takes a looks at the current evidence and if you can take metformin for weight loss.
What is Metformin?
Metformin belongs to the class of medications called “oral hypoglycemics.”
This means it’s taken by mouth to help reduce blood sugar (glucose) levels. For this reason, metformin is commonly used for the management of type 2 diabetes.
How Does Metformin Work?
The way metformin works isn’t fully understood yet.
However, what is known is that it reduces the production of sugar by liver cells (1).
Metformin also improves insulin sensitivity and influences the bacterial community in the gut. It may have anti-inflammatory effects that could be beneficial for metabolic health too (2, 3).
Metformin may also cause weight loss by reducing food intake and blocking gastrointestinal absorption of glucose, at least in theory (4).
Summary: Commonly prescribed for type 2 diabetes, metformin is a medication that influences the metabolism and absorption of sugar.
What is Metformin Used For?
Metformin has been approved for treating type 2 diabetes.
This medication is also sometimes prescribed for the following:
- Gestational diabetes (5)
- Polycystic ovarian disease (PCOS) (6)
- Reducing the risk of diabetes (7).
Research continues on other uses for metformin including:
- Anti-aging or anti-cancer effects (8)
- Helping manage type 1 diabetes (9)
- Reducing the risk of heart disease (10).
Summary: Metformin has been approved for the management of type 2 diabetes. It is sometimes prescribed for other conditions that involve abnormal blood sugar, such as diabetes during pregnancy.
Can You Take Metformin For Weight Loss?
Metformin helps manage type 2 diabetes, a health condition associated with being overweight.
Knowing this, scientists began to wonder if the drug might work by contributing to weight loss. Here are some of their findings:
Weight Loss in Type 2 Diabetes
Exercise and diet are at the first line of defence for type 2 diabetes.
When those aren’t enough, medications such as metformin may be prescribed.
Metformin has been reported to cause an average weight loss of 5% in people with type 2 diabetes (11).
Likewise, Canada’s Clinical Practice Guidelines found that oral hypoglycemics like metformin are associated with 6.6 pounds (3 kg) average weight loss in people with type 2 diabetes.
Keep in mind this is long-term weight loss.
Weight Loss in Polycystic Ovarian Syndrome (PCOS)
Weight loss is often an important part of PCOS treatment.
Metformin has been shown to improve the hormonal profile and reduce weight in women with PCOS (12).
A 2016 meta-analysis found that the use of metformin by women with PCOS resulted in a 0.65% reduction in Body Mass Index (BMI). This works out to be about 2 pounds (1 kg) for a 5’4” (162 cm) woman (13).
So it helps with PCOS, barely.
Weight Loss in Children and Adolescents
According to a 2013 review, metformin may result in short-term weight loss in obese children and adolescents (14).
This weight loss may be the result of metformin’s ability to reduce hunger levels. The impact of metformin combined with lifestyle interventions resulted in “very modest” weight loss in obese adolescents (15, 16).
In an 18-month study of adolescents with high insulin levels, metformin stabilized BMI more than placebo (fake pill) and resulted in a 3% reduction in body fat. No significant weight loss occurred though (17).
Median BMI changes of participants over an 18-month period. The black line represents those taking metformin, the dotted line is those taking a placebo. This diagram suggests metformin helps to prevent weight gain rather than causing weight loss.
Weight Loss for People Taking Anti-Psychotic Medication
Antipsychotic medications like olanzapine and quetiapine are often prescribed for serious issues like bipolar disorder and major depression.
Unfortunately, they can cause weight gain and blood sugar abnormalities.
The use of metformin in combination with these medications has been extensively studied.
Metformin, particularly when combined with lifestyle interventions, can reduce anti-psychotic-induced weight gain. This is true no matter the age (18, 19).
Weight Loss for the General Population
In a study of over 150 people with obesity, several interesting findings emerged (20):
- Metformin resulted in an average weight loss of 13 pounds (6 kg) over 6 months.
- There was a wide range of results. At the extremes, one patient lost 77 pounds (35 kg), another one gained 29 pounds (13 kg).
- Patients who were both obese and insulin resistant lost approximately 2 pounds more than patients without insulin resistance.
- 20% of the patients lost no weight on metformin.
- 6% of those taking metformin gained weight.
- 16.2% of the participants lost at least 10% of their body weight.
- More than 47% of participants lost at least 5 percent of their body weight.
Weight changes in body weight (%) after 6 months of metformin treatment. Metformin users are the dark color, control (placebo) group are the white color. Insulin resistant patients (HOMA >2.5) lost significantly more weight vs patients with normal normal insulin.
In another study with morbidly obese individuals, 28 weeks of metformin treatment led to a drop in average weight from 258 to 245 pounds (117 kg to 111 kg) (21).
So from these results it certainly seems it can help in overweight people, at least for 6 months. And it is even more helpful in those with blood sugar issues.
However, research hasn’t always found metformin to be effective for weight loss.
In a study of 200 overweight young women, lifestyle interventions including structured diet, exercise and behavioural therapy were found to be more effective than metformin for weight loss (22).
Similar results were found in a study of 92 Latina women with pre-diabetes. Lifestyle interventions proved more effective than metformin, which contributed to a weight loss of approximately 2 pounds over the year (23).
Given the conflicting evidence from high quality studies, it suggests that if metformin does cause weight loss, it’s minor.
Summary: Metformin has been linked with weight loss and/or maintenance in certain groups of people including those with type 2 diabetes, polycystic ovarian syndrome and those taking antipsychotic medication. However, metformin does not seem to consistently cause significant weight loss in the general population.
Are There Other Potential Benefits of Metformin?
Metformin appears to have several benefits outside of weight loss.
These include (24, 25, 26):
- Reduced total cholesterol.
- Reduced “bad” cholesterol (LDL)
- Improved blood triglycerides
- Reduced evidence of inflammation
- Reduced insulin resistance.
Summary: In addition to improvement in blood sugar, metformin may have other benefits. These include improved blood lipids and reduced inflammation.
What Are the Side Effects/Risks of Taking Metformin?
Some of the most common metformin side effects include stomach upset, such as:
- Loss of appetite
- Abdominal pain.
It use can also lower vitamin B12 levels, so be aware of that.
Metformin can also result in low blood sugar, but this is rare. It’s more likely to be a problem if a person is not eating enough, drinking alcohol or taking another medication that reduces blood sugar (27, 29).
Metformin can result in a potentially life-threatening increase in blood lactate levels when kidney function is impaired. For this reason, metformin may not be suitable for some people with kidney problems (30).
It may also be unsuitable for people with certain lung and liver conditions.
Summary: Metformin is most commonly associated with gastrointestinal side effects. It can also cause B12 deficiency. More uncommon, but potentially serious, side effects can occur in those with kidney, lung or liver conditions.
Does Metformin Cause Weight Loss?
If you have “pre-diabetes”, type 2 diabetes or are taking antipsychotic medication, metformin may improve the results of your weight loss efforts noticeably.
Additionally, if you are very overweight and are starting to have issues with blood sugar levels (insulin resistance) then it may help ever so slightly. Those with ongoing blood sugar levels issues are better off trying a low-carb diet if given a choice.
However, if you don’t have any of these conditions, metformin will not cause weight loss. Likewise, if you are already underweight it will have little to no negative effects.
In any case, this drug isn’t approved as a weight loss tool and your doctor would not (should not) just prescribe metformin for weight loss.