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Debunking myths about the thyroid and birth control

The thyroid gland is a major player in women's health — including our fertility. When it’s operating the way it’s designed to, it pumps out the right amount of hormones to keep our body systems in check.

But because one in eight women will experience thyroid problems at some point in their lives, keeping an eye on this gland is important. (That’s why we make checking in with your thyroid hormone levels easy with the Modern Fertility test!)

It’s only natural that many of us would want to do a little sleuthing to make sure we’re doing all the right things for a healthy thyroid. If you find yourself Googling the effects of hormonal birth control on the thyroid, chances are you’ll stumble upon a bunch of sites claiming that taking it can do a lot of damage. But… is any of that actually true?

We wanted help parsing out what was worth listening to and what was simply noise, so we reached out to Dr. Eva Luo, an OB-GYN at Beth Israel Deaconess Medical Center and a Health Policy and Management Fellow at Harvard Medical Faculty Physicians, to get to the bottom of this.

Myth 1: Birth control may deplete nutrients (like selenium and zinc) that your thyroid needs to function and produce hormones

The truth: According to Dr. Luo, this is such an infrequent occurrence that it’s not worth letting the rumor turn you off of birth control. Dr. Luo says the only medications that could affect your production of thyroid hormone contain iodine and lithium, and are typically related to chemotherapy, immunotherapy, and antipsychotic treatment — not birth control.

Myth 2: The birth control pill is inflammatory, which can exacerbate autoimmune conditions — including thyroid disorders.

The truth: Dr. Luo says that she’s never heard of this connection between the pill and inflammation. If someone she's treating has autoimmune disease, “That wouldn’t necessarily prevent them from being on oral contraceptive pills,” she explains. Even in cases of thyroiditis, which is generally inflammation of the thyroid, according to Dr. Luo, there are many different reasons that could happen. “It’s definitely not related to the pill,” she says.

Myth 3: Birth control masks symptoms of thyroid disorders

The truth: This is a tricky one. Birth control may temporarily improve symptoms related to conditions like polycystic ovarian syndrome (PCOS) — such as acne and hair growth — and when you stop birth control, underlying issues may be revealed. While it can seem like it was a result of your birth control method, this is not usually the case. We discussed this more in our “5 myths about going off hormonal birth control” Q&A with OB-GYN Dr. Jane van Dis (the clip starts at 16:55).  

While Dr. Luo hasn’t experienced this in her practice, she thinks it is theoretically possible. “Whatever connection there is,” she explains, “It's not very clinically significant. And if it is clinically significant, that's an extremely rare case.”What she does see? Side effects caused by birth control, like weight gain, emotional lability, or changes in energy level. But because the symptoms of hypothyroidism, hyperthyroidism, and other types of thyroid dysfunction are so vague and nonspecific, Dr. Luo says that when presented with a “constellation of symptoms, a good doctor would not just check thyroid hormones, but check those reproductive hormones as well.”

Myth 4: Birth control can lead to increased thyroxine-binding globulin and thyroid dysfunction — and if TBG levels are too high, that will reduce the amount of thyroid hormone flowing through the bloodstream.

The truth: There are studies that confirm this is true to some degree, but the results of just how true it is are inconclusive. According to Dr. Luo, though changes in your thyroid are possible, they’re unlikely to be drastic enough to cause a thyroid disorder.

Why do increased levels of estrogen have the potential to influence thyroid hormones? As Dr. Luo explains it, because reproductive hormones are so similar in structure to thyroid hormones, there can be cross-reactivity when one level is elevated by hormonal birth control.

Here’s a metaphor to help you visualize how this works: Imagine all of your hormones are charms on a bracelet. Hormones all have the same chemical backbone — they’re all attached to identical bracelet chains. What distinguishes the hormones is the different “charms” on them. This is why the body can get confused by the nearly identical estrogen and thyroid “bracelets” and trigger cross-reactivity.

If you have thyroid disease (like hyperthyroidism, hypothyroidism, Hashimoto's, or Graves' disease) and start taking hormonal contraception, Dr. Luo recommends getting your thyroid hormone levels checked three months in. That way, your body has enough time to adjust to the birth control — then your doctor can see if your thyroid medication (a common one is levothyroxine, aka Synthroid) needs a dosage adjustment.

So… should you take birth control if you’re worried about thyroid disorders?

As Dr. Luo explains, any cross-reactivity happening between reproductive hormones and thyroid hormones would only be the result of how similar the hormone structures look. But even in cases where there is cross-reactivity, its clinical impact is low enough that it shouldn’t deter you from managing your reproductive health as you see fit.

If birth control helps you prevent pregnancy (and lead the life you want) but you’re nervous about how it could impact thyroid function, keep an eye on your hormone levels with the Modern Fertility test. You and your doctor can use your results to stay on top of your thyroid health — and make any adjustments to medications or opt for other birth control options if necessary.

This article was medically reviewed by Dr. Eva Marie Luo, an OB/GYN at Beth Israel Deaconess Medical Center and a Health Policy and Management Fellow at Harvard Medical Faculty Physicians, the physicians organization affiliated with the Beth Israel-Lahey Health System.

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Sarah duRivage-Jacobs

Sarah duRivage-Jacobs is a freelance writer and editor who lives in New York City with her creamsicle cat, Jasper. She's obsessed with words (and puns) and doesn't believe in the concept of TMI.

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