Unraveling the Mystery: How Long Does it Take for Metformin to Work?

May 21, 2024
healthy foods and a tape measure

Metformin is a medication used for decades to treat type 2 diabetes. Due to its low-cost and safety profile, it is the first choice for treating diabetes (along with diet and exercise), and the American Diabetes Association (ADA) also recommends using it for treating prediabetes.1

How does metformin work?

In people with type 2 diabetes, insulin is either not produced in high enough quantities, or body tissues are resistant to its effects. This is called insulin resistance. The pancreas continues to pump out more and more insulin, but the body tissues cannot use it effectively. This results in high insulin and high blood sugar levels.

Metformin has the following effects:2

  • Lowering glucose production in the liver
  • Decreasing glucose absorption from the intestines
  • Increasing insulin sensitivity

Metformin does not directly decrease blood sugar like insulin, so it is not used to treat type 1 diabetes. However, it does lower blood sugar, which can have implications for your health. High blood sugar levels damage blood vessels, increasing your risk for cardiovascular disease, kidney disease, and accelerated cognitive decline.

Type 2 diabetes, obesity, and metabolic syndrome are closely related chronic diseases that involve the endocrine system and metabolism. Improving your blood sugar and managing your weight can improve many aspects of your health.

Because of its effects on blood sugar and weight, and its ability to reduce cardiovascular risks and moderate cell growth, metformin has been investigated as an anti-aging, thyroid, and cancer treatment. It is also used off-label to treat polycystic ovary syndrome.3

Proposed mechanisms of action for metformin’s weight loss and metabolic effects include:4

  • Decreasing liver glucose production
  • Altering gut microbiome
  • Suppressing appetite-stimulating brain cells in the hypothalamus
  • Increasing leptin sensitivity
  • Suppressing appetite by increasing lactate production
  • Reversing age-related metabolic changes
  • Altering bile absorption
  • Changing signaling in the gut

Does metformin lower blood sugar immediately?

Metformin does not work like insulin and therefore does not immediately affect your blood sugar.

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

Metformin starts to work within the first few days after starting treatment, but it may take two to three months to get your blood sugars under control.

Metformin is typically prescribed to control your blood sugar. Weight loss is a beneficial side effect. In one study, people who took this medication for up to six months lost an average of 10 to 14 pounds, which was 5.6% to 6.5% of their body weight.5 In another study, participants lost between 4.5% and 6.5% of their body weight after taking metformin as part of a weight loss program.6 A weight loss of 5% of your body weight has been shown to have important health benefits.

What are the signs that metformin is working?

The best way to determine whether metformin is working is to check your blood sugars using blood sugar testing supplies or a continuous glucose monitor. Your doctor may also order a HbA1c. This test measures glycated hemoglobin, an average of your blood sugar over two to three months.

If you are taking metformin for weight loss, check your weight daily, then average your daily weights and record a weekly average. Daily weights fluctuate in response to what you eat, stress, and how much fluid and stool you have in your intestines. A weekly average is more accurate.

Diet weight loss plan using metformin

What is the best time to take metformin?

Metformin is generally taken with meals, either once or twice a day, to mitigate its gastrointestinal side effects. Diarrhea is the most common side effect; slowly increasing the dose can often reduce or prevent metformin-associated diarrhea.

What are potential metformin side effects?

Metformin does not have significant adverse effects, except it can rarely cause lactic acidosis. Symptoms of lactic acidosis include:3,7,8

  • Dizziness
  • Severe drowsiness
  • Muscle pain
  • Tiredness
  • Chills
  • Bluish tinge to skin color
  • Fast breathing
  • Changes in heartbeat
  • Stomach pain
  • Diarrhea
  • Nausea
  • Vomiting

Serious allergic reactions may occur, but they are unusual. Other potential side effects include:

  • Hypoglycemia
  • Gastrointestinal symptoms
  • A metallic taste

Metformin can cause vitamin B12 deficiency. Watch for symptoms associated with vitamin B12 deficiency, such as:

  • Fatigue
  • Muscle weakness
  • Sore, red tongue
  • Mouth ulcers
  • Visual symptoms
  • Pale or yellowing tinge to skin color
healthy foods, capsules and a tape measure

What foods should I avoid when taking metformin?

Glycemic index and glycemic load are two measures that indicate how foods affect blood sugar levels. The glycemic index ranks foods from 0 to 100, with foods assigned a score of 100 having the biggest impact on blood sugar. Pure sugar, for example, is scored as 100. Avoid foods with a high glycemic index. These foods can cause rapid increases in blood sugar. Foods that have a lower glycemic index cause less abrupt increases.

Glycemic load is calculated as the glycemic index multiplied by the amount of carbohydrates in a serving, divided by 100. Foods with a higher glycemic load cause higher peaks in blood sugar than those with a lower glycemic load. Consult International Tables of Glycemic Index and Glycemic Load Values: 2008 for a helpful database of foods with their glycemic index and glycemic load.

Unraveling the Mystery: How Long Does it Take for Metformin to Work?


Metformin synergy combines medications that aid in weight loss and blood sugar control. It can also bring down triglyceride levels, thus lowering the probability of cardiovascular disease. Managing your weight can ultimately decrease your risk of three chronic diseases associated with premature aging: obesity, type 2 diabetes, and cardiovascular disease. Have questions about metformin and how it can improve your health? Contact one of the Invigor Medical treatment specialists today to get all your questions answered.

Frequently Asked Questions

What are the signs that metformin is working?

Signs that metformin is effectively managing blood sugar levels may include stabilized glucose readings, reduced symptoms of hyperglycemia (such as excessive thirst or frequent urination), and improved hemoglobin A1c levels. Regular monitoring of blood sugar levels and ongoing communication with a healthcare provider are crucial to assess the medication’s effectiveness.

How quickly can metformin lower blood sugar?

Metformin typically starts to lower blood sugar levels within a few days to a week of starting treatment. However, the full effects may take several weeks to become evident. It’s essential to monitor blood sugar levels regularly and work closely with a healthcare provider to adjust dosage and monitor progress.

How quickly will you lose weight on metformin?

Weight loss while taking metformin varies from person to person and depends on factors such as diet, exercise, dosage, and individual metabolism. Some individuals may experience gradual weight loss over several months, while others may notice changes more quickly. It’s important to maintain a healthy lifestyle with regular physical activity and a balanced diet to support weight loss efforts.

Does metformin reduce belly fat?

Metformin may contribute to modest weight loss in some individuals, but its primary purpose is to manage blood sugar levels in people with type 2 diabetes. While weight loss can occur as a result of improved glycemic control and decreased insulin resistance, metformin alone may not specifically target belly fat. A comprehensive approach to weight management, including diet, exercise, and medication management, is essential for addressing abdominal obesity.

Author: Leann Poston, M.D.
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  • Nasri H, Rafieian-Kopaei M. Metformin: Current knowledge. J Res Med Sci. 2014 Jul;19(7):658-64. PMID: 25364368; PMCID: PMC4214027.
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  • Scheen AJ, Paquot N. Metformin revisited: A critical review of the benefit-risk balance in at-risk patients with type 2 diabetes. Diabetes Metab. 2013;39:179–90.
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  • Atkinson FS, Foster-Powell K, Brand-Miller JC. International Tables of Glycemic Index and Glycemic Load Values: 2008. Diabetes Care 1 December 2008; 31 (12): 2281–2283.
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