Conditions that affect the thyroid can cause symptoms similar to endometriosis. Part of the endocrine system, the thyroid gland produces hormones that impact every other function in the body.

Endometriosis is not thought to cause thyroid dysfunction, nor is thyroid dysfunction thought to cause endometriosis.

That said, there’s some relationship between thyroid function and endometriosis, explains Bharat Jindal, a board certified OB-GYN.

There have only been a handful of small studies on the topic. “So the exact nature of that relationship is still being studied,” he says.

Thyroid disease is not thought to cause endometriosis. Endometriosis is an idiopathic condition, which means it’s a condition with no known cause.

However, a handful of factors are thought to increase the risk for endometriosis, such as:

Some research suggests that endometriosis can increase your risk of autoimmune-based thyroid disorders.

One 2020 case-control study, for example, found a significant correlation between endometriosis and autoimmune thyroiditis. Autoimmune thyroiditis is also known as Hashimoto’s disease.

Meanwhile, a cross-sectional study published in 2016 suggests a link between endometriosis and Grave’s disease.

Endometriosis and thyroid conditions can have similar symptoms, such as fatigue, weight changes, mood changes, and hair loss, explains Jindal.

As such, it’s common for people with a prior diagnosis — and their clinicians — to assume that these symptoms are exclusively caused by endometriosis. This can lead to a delayed diagnosis of concurrent thyroid conditions.

If the healthcare professional in charge of your endometriosis care hasn’t evaluated your current thyroid function, you might consider making an appointment to discuss this.

Jindal notes that a blood test can be used to measure your thyroid hormone levels. “They may also perform an ultrasound of your thyroid gland,” he says.

This imaging test will allow your clinician to check for visual abnormalities, including changes in texture or size, as well as the presence of any nodules or tumors.

One 2019 review suggests that having a thyroid condition maybe linked with more severe endometriosis symptoms.

Researchers observed that higher levels of thyroid-stimulating hormones (TSH) were linked to a higher risk of endometriosis.

They also noted a positive correlation between the concentration of thyroid hormones and the size of masses or adhesions caused by endometriosis masses.

This led researchers to conclude that because endometrial cells are susceptible to variations in thyroid stimulating hormones, thyroid hormones may increase the severity of endometriosis.

“It’s important to note that correlation does not equal causation,” says Jindal.

In other words, while thyroid conditions may be linked with more severe forms of endometriosis in people who already have the condition, thyroid condition does not cause endometriosis, he says.

Researchers continue to investigate how endometriosis may and may not be connected to thyroid function.

However, people with endometriosis often have concurrent conditions like thyroid disease. That’s why if you have endometriosis, it’s important to understand the potential symptoms of thyroid dysfunction.

If you’re experiencing unusual symptoms, it’s important to make an appointment with a doctor or other healthcare professional. They can help determine the underlying cause and make recommendations for treatment.

Gabrielle Kassel (she/her) is a queer sex educator and wellness journalist who is committed to helping people feel the best they can in their bodies. In addition to Healthline, her work has appeared in publications such as Shape, Cosmopolitan, Well+Good, Health, Self, Women’s Health, Greatist, and more! In her free time, Gabrielle can be found coaching CrossFit, reviewing pleasure products, hiking with her border collie, or recording episodes of the podcast she co-hosts called Bad In Bed. Follow her on Instagram @Gabriellekassel.