Hypothyroidism: symptoms, causes, and treatment

Hypothyroidism is a condition where your thyroid gland doesn’t produce enough of the hormones it’s supposed to. A person can have hypothyroidism for some time before symptoms appear. 

Left untreated, hypothyroidism can contribute to weight gain, low energy, depression, hair loss, brittle nails, fertility problems, joint pain, and more.

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The thyroid is a butterfly-shaped gland that sits in the front of your neck. It produces two main hormones: triiodothyronine (T3) and thyroxine (T4). Hypo” means low, so hypothyroidism just means low thyroid function.  

When you don’t have enough of these hormones, it can affect the way systems in the body function. This includes your metabolism (how you process food and energy), body temperature, hair and nail growth, mood, heart health, and more. 

Thyroid hormones are important throughout our lifespan, but they’re especially important for babies and young children. These hormones help the brain develop, and a lack of them can cause severe, often irreversible symptoms. 

In adults, hypothyroidism may go undiagnosed because symptoms can manifest all over, making it difficult to realize there’s a single underlying condition. Symptoms of hypothyroidism include:  

• Weight gain (a common reason people get tested)

• Feeling sensitive to cold (cold intolerance)

• Muscle weakness

• Tiredness or fatigue

• Hoarse voice

• Constipation

• Dry skin

• Brittle hair and nails 

Around 15% of people don’t show any symptoms at all. Symptoms typically progress slowly, so you may not notice them at first. In some cases, hypothyroidism can only be detected through thyroid function tests, which vary based on age, biological sex, and how long someone has had the condition (Chaker, 2017).

Hypothyroidism can affect every major organ in the body, but the heart system is the most well-studied. Cardiovascular changes can cause issues elsewhere in the body, including fatigue and shortness of breath when exerting yourself. 

Hypothyroidism can lead to higher levels of LDL or “bad” cholesterol. This can impact your metabolism, resulting in weight gain and potentially obesity. By slowing down your metabolism, hypothyroidism also causes your body temperature to drop, which makes you feel colder (Chaker, 2017).

Hypothyroidism can be the result of a problem with the thyroid or in the brain, which controls the release of T3 and T4 from the thyroid gland. 

Hypothyroidism can be caused by a range of different conditions. However, almost all cases of hypothyroidism (about 99%) are caused by a problem in the thyroid gland itself like:

• Autoimmune diseases (where your immune system attacks your thyroid gland)

• Damage to or removal of the thyroid gland

The remaining 1% are caused by malfunctions in the parts of our brain that control the thyroid gland (Chaker, 2017). 

As is true with many conditions, a family history of thyroid problems or autoimmune disorders puts you at higher risk for impaired thyroid function. However, that isn't the only risk factor.

Iodine deficiency is recognized as the most common cause of hypothyroidism worldwide, but iodine deficiency is rare in the United States. In cases where iodine deficiency is not the culprit, an autoimmune disease called Hashimoto's thyroiditis may be the cause (Chiovato, 2019).  

Certain drugs have been linked to hypothyroidism including (Patil, 2021):

• Amiodarone 

• Thalidomide 

• Oral tyrosine kinase inhibitors (sunitinib and imatinib) 

• Stavudine 

• Interferon 

• Bexarotene 

• Perchlorate 

• Rifampin 

• Ethionamide 

• Phenobarbital 

• Phenytoin 

• Carbamazepine 

• Interleukin-2 

• Lithium 

Classes of cancer drugs called anti-CTLA-4 and anti-PD-L1 or PD-1 may also trigger hypothyroidism. A treatment called radioiodine treatment, which uses radioactive iodine to treat hyperthyroidism (when too many thyroid hormones are produced), can overcorrect resulting in an underactive thyroid (Chaker, 2017).

Some people are born with hypothyroidism, a condition known as congenital hypothyroidism. It typically results from an abnormal or missing thyroid gland. Treatment involves thyroid hormone replacement therapy (Chiovato, 2019). 

Hypothyroidism in pregnancy 

Changes in the immune system during pregnancy can trigger hypothyroidism. During pregnancy, the immune system is suppressed and then rebounds after a person gives birth. This rebound is tied to a thyroid condition called postpartum thyroiditis, which can lead to both hypothyroidism and hyperthyroidism (Andersen, 2016; Chiovato, 2019).  

If you’re pregnant, your healthcare provider will likely screen you for warning signs. If you do have hypothyroidism, treatment will depend on the severity (Alexander, 2017; Chiovato, 2019).

Hypothyroidism and cancer

Hypothyroidism can also occur because of thyroid cancer. Keep in mind that having symptoms of hypothyroidism doesn’t automatically mean you have cancer. If you suspect your thyroid might be enlarged, schedule an appointment with a healthcare provider to rule it out (National Cancer Institute, 2021).

People who have had radiation therapy for a benign condition in the neck—such as treatment for an enlarged thymus gland, tonsils, or adenoids—are at a higher risk for developing thyroid cancer. 

Thyroid cancer can be hereditary and is seen most frequently in females. People at the highest risk are those over age 60, people of Asian descent, those with a history of goiter (another thyroid condition), or people with the RET gene mutation (Patil, 2021).

Testing for hypothyroidism usually involves a physical exam and lab tests to check your TSH levels. Even if you don’t have symptoms, the American Thyroid Association recommends people age 35 and older be screened for hypothyroidism and other thyroid disorders every five years (Patil, 2021). 

How the condition is treated varies based on the person and the cause. Iodine supplements may be part of treatment in cases where someone isn’t getting enough iodine.

Hormone replacement medications like levothyroxine are the most common treatment for hypothyroidism in the United States. 

Despite many claims, there really isn’t such thing as a hypothyroidism diet. That said, addressing any nutritional deficiencies is an important part of maintaining thyroid hormone levels and overall health (Chiovato, 2019).  

If you have symptoms of hypothyroidism, check in with a healthcare provider for a blood test to see if you might benefit from treatment.

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Every article on Health Guide goes through rigorous fact-checking by our team of medical reviewers. Our reviewers are trained medical professionals who ensure each article contains the most up-to-date information, and that medical details have been correctly interpreted by the writer.

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Current version

March 15, 2022

Written by

Kaitlin Sullivan

Fact checked by

Yael Cooperman, MD

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About the medical reviewer

Yael Cooperman, MD, Ro

Yael Cooperman is a physician and works as a Senior Manager, Medical Content & Education at Ro.