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Hashimoto’s disease and hypothyroidism are related thyroid disorders, but they are not the same. 

The term hypothyroidism refers to an underactive thyroid, leading to low levels of thyroid hormones in the body. It can be caused by various underlying conditions and can lead to a range of health issues if left untreated. 

Hashimoto’s disease belongs to a group of conditions called autoimmune thyroid disorders. Like with other autoimmune conditions, in people with Hashimoto’s disease, the body’s immune system attacks and damages healthy tissue, in this case, in the thyroid gland. This leads to reduced thyroid hormone production or hypothyroidism. Hashimoto’s disease is the most common underlying cause of hypothyroidism in the United States. 

Please continue reading to learn more about the difference between Hashimoto’s vs hypothyroidism.

Is Hashimoto's disease the same thing as hypothyroidism?

No, Hashimoto’s disease is not the same thing as hypothyroidism, although the terms are sometimes (wrongly) used interchangeably. While both conditions can be present with the same types of symptoms as a result of low thyroid hormone levels, their causes are different. 

Hashimoto’s disease is a specific medical condition. It is a chronic autoimmune disease in which the body’s immune system mistakenly attacks and destroys thyroid tissue. Large numbers of white blood cells collect in the thyroid tissue and prevent it from functioning properly.

Other names for this autoimmune disorder include Hashimoto’s thyroiditis, chronic lymphocytic thyroiditis, and chronic autoimmune thyroiditis. Hashimoto’s can be related to other autoimmune disorders such as celiac disease, pernicious anemia, rheumatoid arthritis, and adrenal insufficiency.

The destruction of thyroid tissue in people with Hashimoto’s disease leads to decreased thyroid hormone production. This is called hypothyroidism or an underactive thyroid gland.

In the United States and many other parts of the world, Hashimoto’s disease is the most common cause of hypothyroidism. Other causes of hypothyroidism include:

• Thyroiditis (inflammation of the thyroid)

• Surgical removal of the thyroid 

• Radiation treatment involving the neck

• Congenital hypothyroidism (present since birth)

• Side effects of certain medications, such as iodine-containing medications used to treat abnormal heart rhythms and certain drugs prescribed for mental health conditions such as bipolar disorder

• Pituitary diseases (rare)

• Excess iodine or iodine deficiency in the diet (rare)

Are thyroid hormone levels low or high in Hashimoto’s?

Thyroid hormone blood levels can be normal, low, or high in people with Hashimoto’s disease. As mentioned, Hashimoto’s is an autoimmune condition that destroys thyroid tissue. In the early stages, the destruction of thyroid tissue may not be severe enough to affect thyroid hormone production, and therefore, thyroid hormone levels may remain normal. 

Over time, as the disease progresses, Hashimoto’s thyroiditis may lead to low levels of T4 and T3 hormones in the body because the destroyed thyroid gland is unable to make enough thyroid hormones. This is called hypothyroidism, a condition in which the body’s functions slow down. 

In some people, Hashimoto's initially causes an enlarged thyroid gland or goiter. This is called hashitoxicosis and leads to overactivity of the thyroid gland (hyperthyroidism). It is associated with increased thyroid hormone formation and high thyroid hormone levels. However, this is temporary and almost always followed by hypothyroidism.

Can you have Hashimoto's without hypothyroidism?

Yes, you can have Hashimoto thyroiditis without overt hypothyroidism. In some people with Hashimoto’s, the thyroid gland is not severely damaged and continues to make enough thyroid hormone. Such people may test positive for Hashimoto’s disease but have normal thyroid hormone blood levels and no symptoms of hypothyroidism or subclinical hypothyroidism. 

In such people, healthcare providers typically recommend observation and monitoring with periodic thyroid function tests. If thyroid hormone blood levels are found to be low on a blood test or you develop hypothyroidism symptoms in the future, then treatment can be started with thyroid hormone medicine.

What are the thyroid gland and thyroid hormones?

The thyroid is a small, butterfly-shaped gland located in the anterior part of the neck. The thyroid makes two main hormones: thyroxine (T4) and triiodothyronine (T3). According to the National Institute of Diabetes and Digestive and Kidney Diseases and the American Thyroid Association, thyroid hormones play an important role in regulating many bodily functions, including metabolism, heart rate, breathing, body temperature, brain development, fertility, and skin and bone maintenance. Thyroid function, therefore, affects nearly every organ in the body.

What causes Hashimoto’s thyroiditis?

Scientists are not sure what exactly causes Hashimoto’s disease, but both genetic and environmental factors are believed to play a role. A family history of thyroid disease and viruses such as hepatitis C can put you at a higher risk of Hashimoto’s disease. 

What test confirms Hashimoto's disease?

In addition to obtaining a detailed medical history and performing a physical exam, your doctor may order the following blood tests to check for hypothyroidism and confirm Hashimoto’s disease:

• Thyroid-stimulating hormone (TSH): TSH is produced by the pituitary gland in the brain. When the pituitary gland detects low levels of thyroid hormones in the blood, it increases TSH production, which, in turn, prompts the thyroid gland to increase thyroid hormone production. Therefore, high TSH levels are indicative of hypothyroidism.

• Thyroid hormone (T4) levels: Thyroxine (T4) is the main thyroid hormone. Low blood levels of free thyroxine (T4) confirm the findings of a high TSH and tell us that the problem is in the thyroid gland.

• Thyroid antibodies: More than one thyroid disease can lead to hypothyroidism. A thyroid peroxidase (TPO) antibody test tells us if Hashimoto's disease is the cause of hypothyroidism. TPO antibodies are proteins that target healthy thyroid cells. Most people with Hashimoto's disease have TPO antibodies detected in their blood.

Note: Your doctor may order additional tests, such as an ultrasound imaging test of the thyroid gland, if they suspect thyroid nodules or thyroid cancer.

How does hypothyroidism (underactive thyroid gland) make you feel?

Common symptoms of hypothyroidism include fatigue, weight gain, depression, cold intolerance, muscle pain, joint pain, dry skin, thinning hair, heavy or irregular menstrual cycle, fertility problems, constipation, and a slow heart rate.

How does Hashimoto's make you feel? 

Hashimoto’s disease typically does not cause any symptoms in the early stages. However, as the disease progresses, symptoms of Hashimoto’s disease develop, which are similar to the symptoms of hypothyroidism (see above). Check out “8 Signs You May Have a Thyroid Condition.”

How do doctors treat hypothyroidism and Hashimoto's?

Treatment for Hashimoto’s disease depends on whether your thyroid is damaged enough to cause hypothyroidism. If you don’t have any symptoms and your thyroid hormone levels are normal, your doctor may simply monitor you with regular physical exams and blood tests.

If you have hypothyroidism caused by Hashimoto’s disease, thyroid hormone replacement with a medication called levothyroxine (sold under the brand name Synthroid and others) can provide symptom relief. 

This medication is a synthetic version of the natural thyroid hormone thyroxine (T4). It is the standard treatment for hypothyroidism according to American Thyroid Association guidelines. Levothyroxine is available as a tablet, capsule, and liquid to take by mouth on an empty stomach once daily in the morning.

Check out our blog, “What Are Some Signs My Thyroid Medication Is Not Working?”