General Warnings

Metformin Side Effects In Women

Metformin is a commonly prescribed medication for type 2 diabetes that has been used for over 60 years. It may also be used to treat other medical conditions, such as polycystic ovary syndrome (PCOS) and metabolic syndrome.

Metformin is a member of the biguanide class of drugs and works by reducing glucose production in the liver and increasing glucose uptake by muscle and adipose tissue. This results in improved blood glucose control and reduced insulin resistance.

The use of metformin among women depends on the prevalence of the medical conditions it is used to treat. For example, PCOS is estimated to affect up to 10% of women of reproductive age and is a common condition for which metformin may be prescribed. The use of metformin among women with PCOS varies, but studies have suggested that up to 70% of women with PCOS may be prescribed metformin.

In general, the use of metformin among women for the treatment of diabetes or other medical conditions is relatively common. However, the exact prevalence of metformin use among women varies depending on the population being studied and the specific medical conditions for which it is being used Although generally considered safe and effective, metformin can cause side effects, especially in women.

In this article, we will discuss the various side effects of metformin in women in detail. We will cover both common and uncommon side effects, as well as potential risks and precautions.

Common Side Effects

  • Gastrointestinal (GI) Upset: The most common side effect of metformin is GI upset, which can include diarrhea, nausea, vomiting, and abdominal discomfort. These symptoms usually occur within the first few weeks of starting the medication and typically resolve with continued use. To minimize GI symptoms, it is recommended to start with a low dose and gradually increase as tolerated, take the medication with food, and avoid high-fat meals.
  • Lactic Acidosis: Lactic acidosis is a rare but potentially life-threatening side effect of metformin. It occurs when there is an accumulation of lactic acid in the blood, which can lead to acidosis, organ failure, and even death. Women with pre-existing kidney, liver, or heart disease are at an increased risk of developing lactic acidosis when taking metformin. Symptoms include weakness, fatigue, muscle pain, difficulty breathing, and abdominal discomfort. If these symptoms occur, medical attention should be sought immediately.
  • Hypoglycemia: Although uncommon, metformin can cause hypoglycemia (low blood sugar) when taken with other diabetes medications such as sulfonylureas or insulin. Symptoms of hypoglycemia include shakiness, dizziness, sweating, confusion, and loss of consciousness. Women taking metformin should be aware of the signs and symptoms of hypoglycemia and have a plan in place to treat it if it occurs.
  • Vitamin B12 Deficiency: Metformin can interfere with the absorption of vitamin B12, which can lead to a deficiency over time. Symptoms of B12 deficiency include fatigue, weakness, tingling or numbness in the hands and feet, and cognitive decline. Women taking metformin should have their B12 levels monitored regularly and may require supplementation if deficient.
  • Weight Loss: Metformin can cause weight loss in some women, which can be a desirable side effect for those with type 2 diabetes who are overweight or obese. The exact mechanism by which metformin promotes weight loss is not fully understood but may be related to decreased appetite, increased satiety, and improved insulin sensitivity.

Uncommon Side Effects

  • Rash: Although uncommon, metformin can cause a rash or other skin reactions in some women. These may include hives, itching, and redness. If a rash occurs, the medication should be discontinued and medical attention sought.
  • Metallic Taste: Metformin can cause a metallic taste in the mouth, which may be bothersome to some women. This side effect is usually mild and may improve over time.
  • Changes in Menstrual Cycle: Metformin may cause changes in the menstrual cycle in some women, including irregular periods, heavy bleeding, or cessation of periods altogether. These changes are usually temporary and may improve with continued use of the medication.
  • Decreased Libido: Metformin may decrease libido (sex drive) in some women, although the mechanism is not well understood. This side effect is rare and usually reversible upon discontinuation of the medication.
  • Hypothyroidism: Metformin can interfere with thyroid function in some women, leading to hypothyroidism (underactive thyroid). Symptoms of hypothyroidism include fatigue, weight gain, cold intolerance, dry skin, and constipation. Women taking metformin should have their thyroid function monitored regularly.
  • Headache: Headache is an uncommon side effect of metformin and usually resolves with continued use of the medication.
  • Muscle Weakness: Metformin can cause muscle weakness in some women, although this side effect is rare. Women with pre-existing muscle weakness or myopathy may be at an increased risk of developing this side effect.
  • Liver Toxicity: Although rare, metformin can cause liver toxicity, especially in women with pre-existing liver disease. Symptoms may include abdominal pain, nausea, vomiting, and yellowing of the skin and eyes (jaundice). Women taking metformin should have their liver function monitored regularly.

Potential Risks and Precautions

1.      Kidney Function: Metformin is primarily excreted by the kidneys, and women with impaired kidney function may be at an increased risk of developing lactic acidosis. Therefore, metformin is contraindicated in women with a creatinine clearance (a measure of kidney function) of less than 30 ml/min.

2.      Heart Disease: Metformin has been shown to have cardiovascular benefits and is often prescribed to women with type 2 diabetes and heart disease. However, in rare cases, metformin can cause heart problems, such as congestive heart failure or myocardial infarction (heart attack). Women with pre-existing heart disease should be monitored closely while taking metformin.

3.      Pregnancy: Metformin is considered safe to use during pregnancy, although there is limited data on its safety and efficacy. Women with type 2 diabetes who are pregnant or planning to become pregnant should consult with their healthcare provider to discuss the risks and benefits of metformin.

4.      Breastfeeding: Metformin is excreted in breast milk, although the amount is small and unlikely to cause harm to the nursing infant. However, women who are breastfeeding should discuss the use of metformin with their healthcare provider.


Metformin is a commonly prescribed medication for type 2 diabetes that can cause side effects, especially in women. Common side effects include gastrointestinal upset, lactic acidosis, hypoglycemia, vitamin B12 deficiency, and weight loss. Uncommon side effects include rash, metallic taste, changes in the menstrual cycle, decreased libido, hypothyroidism, headache, muscle weakness, and liver toxicity. Women with pre-existing kidney, liver, or heart disease may be at an increased risk of developing side effects. Women who are pregnant or breastfeeding should consult with their healthcare provider before taking metformin. Regular monitoring of kidney function, liver function, B12 levels, and thyroid function is recommended for women taking metformin.


Dr. Oche Otorkpa PG Cert, MPH, PhD

Dr. Oche is a seasoned Public Health specialist who holds a post graduate certificate in Pharmacology and Therapeutics, an MPH, and a PhD both from Texila American University. He is a member of the International Society of Substance Use Professionals and a Fellow of the Royal Society for Public Health in the UK. He authored two books: "The Unseen Terrorist," published by AuthorHouse UK, and "The Night Before I Killed Addiction."
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