Metformin is a medication used to help control blood sugar levels and increase sensitivity to insulin.
Because these are common complications of polycystic ovary syndrome (PCOS), metformin is frequently prescribed to treat this hormone disorder.
In this article, we’ll explore how metformin works for PCOS, as well as its side effects and alternative treatment options.
We’ll also discuss precautions and risks that you need to be aware of to safely take metformin.
What Is Metformin?
Metformin is approved by the U.S. Food and Drug Administration (FDA) for the treatment of type 2 diabetes mellitus.
It is also approved by the American Diabetes Association for treating prediabetes and may be used by healthcare providers to treat PCOS.
Metformin is in a class of drugs known as biguanides.
It works to normalize blood glucose levels by preventing the liver from making too much sugar, decreasing how much glucose the intestines absorb, and increasing sensitivity to the hormone insulin.
It is sold as a generic and under the brand names Glucophage, Fortamet, and others.
Metformin for PCOS
Symptoms vary, making it hard to diagnose in some cases.
Symptoms of PCOS can include:
- Menstrual cycle irregularity
- Pelvic pain
- Hirsutism (excess hair growth on the face)
- Weight gain or problems losing weight
- Insulin resistance and high glucose
- Patches of thick, dark skin
- Cysts on ovaries
Metformin is used to treat PCOS because it can address insulin resistance and high blood sugar, which may in turn positively affect other aspects of the disorder.
It is usually used along with other treatments.
What does Metformin do for PCOS?
Metformin prevents the liver from making glucose and decreases intestinal absorption of glucose.
This leads to lower blood sugar levels, which can improve the body’s response to insulin.
As a result, metformin may promote hormone balance, weight loss, and improved metabolic health.
Metformin may also support better outcomes for people who have PCOS and are pregnant, such as a reduced risk of preterm delivery and gestational diabetes.
Metformin Side Effects
Metformin can cause some mild side effects that may improve over time as your body adjusts to the medication.
Tell your healthcare provider if side effects do not improve or worsen.
Common side effects of metformin are:
- Diarrhea: Metformin changes the way that the intestines absorb glucose. This leads to the formation of lactic acid, which can irritate the intestinal lining. Healthcare providers typically start patients on low doses so that the body can adjust. This can decrease the severity of diarrhea.
- Nausea and vomiting: Though nausea is common, vomiting happens less frequently. To decrease gastrointestinal upset, take metformin with meals.
- Intestinal discomfort: Bloating, gas, and other intestinal pains may happen in response to the ways that metformin changes the body’s response to glucose. These effects usually wear off with time and may be decreased if metformin is taken with food.
- Headache: Metformin prevents the liver from making glucose. Medications that have a direct effect on the liver may cause mild headaches initially.
- Metallic taste in mouth: Around three in every 100 people who take metformin may temporarily notice an unpleasant taste in the mouth.
- Weight loss: While metformin is not a weight-loss drug, because it helps balance insulin and glucose responses in the body, it may lead to some weight loss. Insulin resistance and high glucose levels are often a cause of weight gain in type 2 diabetes and related conditions, so metformin may help offset this effect.
Less commonly, metformin can cause some serious side effects:
- Hypoglycemia: When metformin is combined with intense exercise, other diabetes medications, dietary nutritional imbalances, or higher alcohol intake, low blood sugar known as hypoglycemia may occur. Symptoms include lightheadedness, tiredness, feelings of physical weakness, nausea, vomiting, and a too fast or too slow heart rate.
- Anemia: Metformin makes it harder for the body to absorb vitamin B12. Low levels of B12 can cause anemia. Symptoms include extreme tiredness, dizziness, and feeling cold all the time. Over time, B12 deficiency can cause numbness and tingling, mood changes, poor energy, hair loss, and brain fog. Your healthcare provider can check your red blood cell and iron levels to determine if you are anemic. Vegetarian or vegan diets may increase this risk.
- Lactic acidosis: The FDA has given metformin a black box warning for the risk of lactic acidosis. This happens when too much metformin builds up in the body, causing high levels of lactic acid. Symptoms include dizziness, lightheadedness, feeling cold, muscle pain, extreme tiredness, decreased appetite, nausea, vomiting, trouble breathing, a heart rate that is too fast or too slow, sudden reddening of the skin, or feelings of warmth. This medical emergency can be fatal. Get emergency medical care immediately if you notice signs of lactic acidosis.
To decrease the chance of serious complications and side effects, ask your healthcare provider how to safely take metformin.
Other Treatment Options for PCOS
There is no cure for PCOS, but you can manage it with lifestyle and dietary changes as well as medication.
Though metformin is not the only medication for PCOS, it is commonly used.
Alternative medications to treat PCOS include:
- Letrozole: This breast cancer drug may be used in PCOS specifically to stimulate the ovaries for normal ovulation. This is usually done in combination with fertility treatments.
- Gonadotropins: These injectable medications provide hormones to bring balance for PCOS. They are often used in fertility treatment or in vitro fertilization (IVF).
- Eflornithine: This medication addresses excessive facial hair.
Other drugs help promote better insulin or glucose responses in the body:
- Sulfonylureas: These help improve the production of insulin, which can help reduce blood sugar levels. Glyburide (DiaBeta, Micronase, others), glimepiride (Amaryl), and glipizide (Glucotrol) are examples. However, these have a higher risk of causing low blood sugar, so they are less commonly used than metformin.
- Meglitinides: These help increase insulin production and help the body release more insulin in response to meals. Examples include repaglinide (Prandin) and nateglinide (Starlix).
- Thiazolidinediones: These medications decrease insulin resistance and include rosiglitazone (Avandia) and pioglitazone (Actos). Because these medications may have more serious side effects, they are not the first choice for managing high blood sugar.
Precaution and Risks
Metformin is typically taken long-term, possibly for months or years.
The largest risk associated with taking metformin long-term is anemia.
Inform your healthcare provider of all prescription and OTC medications as well as supplements that you take.
Metformin comes with possible drug interactions, which can increase the risk for serious adverse events.
The following have interactions with metformin:
- Bupropion (Wellbutrin, Aplenzin)
- Carbonic anhydrase inhibitors
- Ethanol (alcohol)
- Iodinated contrast agents
- Alpha-lipoic acid
- Selective serotonin reuptake inhibitors (SSRIs)
- Other diabetes medications
Additionally, metformin is not safe to take before radiology procedures with iodine contrast or if you have any of the following medical conditions:
- Kidney problems or disorders
- Before surgical procedures
- Metabolic acidosis
- Heart failure
When to See a Medical Provider
If you have signs of PCOS, a healthcare provider can run tests to make a proper diagnosis.
If you have PCOS, a healthcare provider can help you manage symptoms, medications, and treatments to improve quality of life.
How PCOS is managed depends on your age, health history, symptoms, and whether you are trying to get pregnant.
How K Health Can Help
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Frequently Asked Questions
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Diabetes basics. (2022).
Metformin: Current knowledge. (2014).
Polycystic ovary syndrome. (2021).
PCOS (polycystic ovary syndrome) and diabetes. (2020).
Role of metformin in the management of polycystic ovary syndrome. (2010).
Metformin use in women with polycystic ovary syndrome. (2014).
Combined lifestyle modification and metformin in obese patients with polycystic ovary syndrome. A randomized, placebo-controlled, double-blind multicentre study. (2006).
Effects of metformin on pregnancy outcomes in women with polycystic ovary syndrome. (2016).
Glucophage (metformin hydrochloride) tablets. (2017).
Pharmacokinetics of metformin in patients with gastrointestinal intolerance. (2018).
Taste of a pill: organic cation transporter-3 (OCT3) mediates metformin accumulation and secretion in salivary glands. (2014).
Metformin information. (2016).
Metformin-associated lactic acidosis: Current perspectives on causes and risk. (2016).