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Can birth control cause hypothyroidism?

Shannon

Written by Shannon Donohue

Shannon Donohue

Shannon Donohue is a professional writer with more than five years of experience. Her work explores women's empowerment, health, travel, and technology. She is a lover of learning with a passion for advocacy. She believes that knowledge is power and allows that belief to guide her work. She earned a degree in Journalism from Marist College and is based in New York City.  
Maya

Fact checked by Maja Garbulinska, Scientist at Natural Cycles

Maja Garbulinska

Maja Garbulinska holds Master’s in Health Data Science from Harvard University. Maja joined Natural Cycles driven by her passion for advancing female and reproductive health. She has several years of experience working with data science and machine learning in Swiss biotech industry.

Follows NC° Editorial Policy

Follows NC° Editorial Policy

 At Natural Cycles, our mission is to empower you with the knowledge you need to take charge of your health. At Cycle Matters, we create fact-checked, expert-written content that tackles these topics in a compassionate and accessible way. Read more...

Key takeaways:

  • Hypothyroidism is a condition where your body doesn’t produce enough thyroid hormone
  • Hormonal birth control can alter levels of certain hormones in your body, including hormones related to the thyroid
  • Studies on the relationship between hormonal birth control and hypothyroidism are limited and contradictory 
  • Talk to your healthcare provider about the best options and treatments to address any concerns you have about thyroid function

Did you know that hypothyroidism affects an estimated one in 300 people in the United States? [1] Odds are you know someone with the condition whether that’s at work or in your family or friend group.

Hypothyroidism is when the thyroid gland doesn’t make enough of the thyroid hormone, which has the function of regulating the way your body uses energy. Also known as underactive thyroid, it can cause symptoms like fatigue, weakness, feeling abnormally cold, and more. It’s more common in women and people over the age of 50. [2]

The relationship between hormonal birth control and hypothyroidism is still being explored by the medical community. More research is needed on the topic, but since hypothyroidism is a hormonal condition, some studies suggest that using hormonal birth control may affect your risk factors for hypothyroidism and other thyroid-related disorders. [3]

In this article, we’ll go through a Q&A to address some of the most common queries about the relationship between birth control and hypothyroidism, starting with the key question:

Can birth control cause hypothyroidism?

The short answer is: we don’t know. Like many areas of women’s health, this is an area that has been historically underfunded and not studied extensively. Furthermore, the studies that are available on this subject have unfortunately produced contradictory results. It is also worth noting that not all hormonal birth control options are equal, with different hormones having different effects on thyroid function.

One of the first studies on this topic was done in 2012, and it worked with a sample size of about 5,000 adult women. It concluded that there was a slightly higher chance of developing hypothyroidism if the patient had been using hormonal birth control for more than 10 years. [3] It is important, however, to remember that just because two things seem connected doesn’t necessarily mean that one causes the other. Other factors may be involved, so more research is needed to prove if one thing directly causes the other.

With this in mind, it’s difficult to make a direct connection between hormonal birth control and hypothyroidism. However, we know that hypothyroidism is a hormonal condition, so it’s worth exploring the topic of how hormonal birth control potentially affects the thyroid.

What is hypothyroidism?

Let’s get into some details about hypothyroidism and what it is exactly. The thyroid is a small butterfly-shaped gland located in the front of your neck, and it’s a very important organ in the endocrine system (the system that regulates our hormonal health). The thyroid gland produces thyroid hormones, which regulate the way your cells use energy (also known as your metabolism). When the thyroid is underactive and not producing enough of those hormones, it affects your metabolism which can affect everything from organ function to energy levels to your skin. [2]

Symptoms of hypothyroidism:

Some common early symptoms of hypothyroidism include:

  • Feeling unusually cold, like needing a sweater when everyone else in the room is in sleeveless shirts
  • Fatigue or generally feeling more tired than others
  • Sadness or even depression
  • Joint weakness or pain
  • Muscle weakness or pain
  • Heavy or irregular periods

If untreated, more symptoms of hypothyroidism could arise over time including:

  • Slow speech
  • A decrease in sense of taste and smell
  • Puffiness in the face, hands, and feet
  • Eyebrow thinning
  • Slow heart rate

Seeking medical support is important if you experience any of the above symptoms. If left untreated, hypothyroidism can increase the risk of infertility, miscarriage, birth defects, heart disease, heart failure, and general infection. Luckily, hypothyroidism is a treatable and manageable condition. A healthcare provider can do a comprehensive assessment to check your symptoms and diagnose the condition, which usually includes a physical exam and a blood test. [2]

Infertility and hypothyroidism 

We know that infertility is a sensitive topic, and if you’re currently exploring birth control options, you may not be thinking about getting pregnant in the next few years. But it’s worth noting that the hypothyroidism condition can affect your fertility in the future. It's been associated with anovulatory cycles where you don’t ovulate, issues with the luteal phase, and sex hormone imbalance (particularly, high levels of prolactin in the blood). [4]

Subclinical hypothyroidism has also been shown to significantly affect fertility. This is a milder form of thyroid dysfunction where thyroid hormone levels are within the normal range but the levels are elevated for the thyroid-stimulating hormone (the hormone produced in your brain that controls the thyroid activity). Those with subclinical thyroiditis might not have any obvious symptoms but they might find it harder to get pregnant.[5]

The good news is that one study showed that 76.6% of infertile women diagnosed with hypothyroidism conceived within 6 weeks to one year after beginning treatment for hypothyroidism. The authors of that study recommended testing for hypothyroidism in the early stages of infertility consultations because treatment (often a daily pill called levothyroxine that restores normal levels of the thyroid hormone) is much less invasive and less costly than other infertility treatments. [4] So if your fertility issues are diagnosed to be caused by low thyroid hormone levels, the chances of a relatively simple oral thyroid hormone success at improving fertility are high.

Can birth control pills affect thyroid test results?

If you and your healthcare provider suspect that you have hypothyroidism, the next step is testing for the condition. This is done via a physical exam of the thyroid gland itself and blood tests to assess the levels of thyroid and thyroid-stimulating hormones in your blood. Sometimes, a specialist might decide to perform an ultrasound examination of your thyroid. This procedure is quick and painless.

T4 is the main form of thyroid hormone that circulates in your body and helps regulate how your body uses energy. Doctors test for its levels to make sure your thyroid is functioning as it should. T4 is measured in three ways on these blood tests: 

  • Bound T4 is attached to binding proteins, and these proteins allow it to travel through your bloodstream to your organs and tissues.
  • Free T4 detaches from those binding proteins to enter the tissues and organs and get to work on regulating your body’s energy usage.
  • Total T4 tests measure both the “Bound” and “Free” types of T4 in your body. 

Estrogens like those found in hormonal birth control pills can increase levels of binding proteins, thus raising the Total T4 measurement on thyroid tests. Remember that hypothyroidism indicates low levels of T4, so if hormonal birth control is synthetically raising levels of Bound T4, the test results may be inaccurate, showing normal (or even high) levels. [6]

Thyroid blood tests also measure a hormone called thyroid stimulating hormone (commonly referred to as TSH) which is produced by the pituitary gland in the brain, and estrogen levels typically do not affect this hormone. The main job of TSH is to stimulate the thyroid gland to produce thyroid hormones, so high TSH usually indicates that the body is not making enough of the thyroid hormone. Testing for high TSH and Free T4 specifically will usually provide more accurate thyroid test results if you are taking birth control pills or have excess estrogen in the body for other reasons, like pregnancy. [6]

Can birth control affect the thyroid gland?

Because the excess estrogen from birth control pills actually increases the binding proteins in your body rather than the thyroid hormones directly, it’s still not understood if and how hormonal birth control affects the thyroid itself. It definitely affects thyroid test results though, which can complicate conversations with your healthcare provider and treatment. Remember to ask for TSH and free T4 tests specifically.

How does birth control affect hypothyroidism medication?

If you do get a hypothyroidism diagnosis and start taking medication for it (levothyroxine is the most common drug available that rebalances levels of T4), you may be wondering if the medicine will affect your birth control. 

While levothyroxine should not affect the efficacy of hormonal birth control, this type of contraception might influence the levels of thyroid hormones in the body for some individuals with hypothyroidism. 

So, if you’re just starting hormonal birth control or looking to stop using it, your healthcare provider may recommend an adjustment of the levothyroxine dosage depending on how your thyroid is functioning. They’ll likely want to perform thyroid tests regularly over the course of a few months of starting or stopping hormonal birth control and adjust the levothyroxine dosage accordingly. [7]

Can hormonal birth control affect Hashimoto's disease?

Hashimoto’s disease is another low thyroid hormone condition, but it is classified as an autoimmune disorder where your immune system makes antibodies that actively attack the thyroid. This attack lowers levels of thyroid hormone, and can therefore lead to a hypothyroidism diagnosis.

Hashimoto’s is also more common in women than men, but it’s not clear whether or not birth control affects the condition. The most common risk factors for Hashimoto’s include your family history and the presence of another autoimmune disease, neither of which would be affected by whether or not you use hormonal birth control. [8]

Can hypothyroidism cause other hormonal imbalances?

Yes, an underactive thyroid can lead to other hormonal imbalances and issues. Often, when one hormone level is abnormal, it affects others as they all operate interdependently within your endocrine system. 

For women specifically, hypothyroidism is associated with other hormonal effects such as heavy or irregular periods, low sex drive, a lack of ovulation, preeclampsia, miscarriage, and abnormal bleeding after birth. [9, 10, 11] 

Remember that while this may sound scary, hypothyroidism is completely treatable and much more common in women over 50, so many of these more extreme effects that may happen during reproductive years are less common.

When to see a doctor

If you are experiencing any unusual symptoms or suspect that you have hypothyroidism or any other type of hormonal imbalance, it’s best to consult a healthcare professional for proper testing and treatment. Hormone interactions are quite complex, your doctor can help you make the right decision for your body and lifestyle.

Switching to hormone-free birth control

Depending on your situation and risk factors, one suggestion your provider may have for you is switching birth control methods and/or using a non-hormonal birth control method instead of hormonal contraception. Again, while there is limited evidence to suggest a direct relationship between hypothyroidism and hormonal birth control, it may be interesting to get a sense of how your body functions and feels without synthetic hormones.

Skip the side effects with Natural Cycles

If you’re considering going hormone-free and looking for a non-invasive birth control option, Natural Cycles may be right for you. It’s the first FDA Cleared birth control app of its kind, it uses the science of your body temperature to find your fertile window so you can plan or prevent pregnancy hormone-free. Natural Cycles annual plan includes a free thermometer, but is also compatible with Apple Watch and Oura Ring, allowing you to measure seamlessly overnight. Get started today!

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