Hypothyroidism is when the thyroid gland does not produce enough thyroid hormones, whereas hyperthyroidism is when the thyroid gland produces too much. The conditions have different symptoms and causes.

The thyroid gland is a butterfly-shaped gland at the center of the neck. It produces hormones that regulate the body’s metabolism. The main hormones the thyroid produces are thyroxine and triiodothyronine.

If someone has a thyroid condition, it means their thyroid gland is not producing hormones as it should.

Hyperthyroidism and hypothyroidism are separate conditions with different symptoms. “Hyper” means the gland produces too much of the thyroid hormones, while “hypo” means it produces too little thyroid hormones.

The American Thyroid Association estimates that 20 million people in the United States have some form of a thyroid condition.

This article discusses the differences between hyperthyroidism and hypothyroidism.

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Hypothyroidism, or underactive thyroid, is when the thyroid gland does not produce enough hormones.

Thyroid hormones control the ways in which the body uses energy and affects the majority of organs in the body.

Without enough thyroid hormones, many functions in the body will slow down.

Hyperthyroidism, also known as overactive thyroid, is a condition in which the thyroid produces too much of the thyroid hormones.

This can cause bodily functions to speed up.

Hyperthyroidism and hypothyroidism can cause opposite symptoms.

With hypothyroidism, the lack of thyroid hormones can slow down some bodily functions, which can cause:

  • slowed heart rate
  • weight gain
  • difficulty tolerating the cold
  • depression

With hyperthyroidism, the overproduction of thyroid hormones can speed up bodily functions. This can result in:

  • a rapid or irregular heartbeat
  • weight loss
  • difficulty tolerating heat
  • irritability, nervousness, and anxiety

The following are symptoms of hypothyroidism and hyperthyroidism.


There are many symptoms that can vary between people.

Symptoms include:


While some symptoms of hyperthyroidism are easy to spot, others are only visible in somebody with an advanced condition.

Key signs and symptoms of hyperthyroidism include:

In some cases, medical professionals can mistake hyperthyroidism for dementia or depression. Older adults may also experience different symptoms, such as a loss of appetite.

The following are the causes and risk factors for each condition.


Thyroid stimulating hormone (TSH) is produced by the pituitary gland. TSH triggers the thyroid to produce thyroxine (T4) and triiodothyronine (T3).

Hypothyroidism occurs when TSH levels are high, but T4 and T3 are at normal levels.

Causes can include:

  • Hashimoto’s thyroiditis, an autoimmune condition that results in the body attacking the thyroid gland
  • thyroiditis, or inflammation of the thyroid
  • complete or partial surgical removal of the thyroid
  • radioactive iodine, a treatment for hyperthyroidism
  • medications, including some that treat heart conditions, bipolar disorder, and cancer

Some people are born with hypothyroidism, which is called congenital hypothyroidism. This can happen when the thyroid is not fully developed.

Although this happens less often, an iodine deficiency can cause hypothyroidism. However, this is very rare in the United States.


The most common cause of hyperthyroidism is Graves’ disease. Graves’ disease is an autoimmune disease where the body’s immune system attacks the thyroid gland. This causes the thyroid gland to release too much of the thyroid hormones.

Other causes of hyperthyroidism can include:

  • overactive thyroid nodules, or lumps on the thyroid
  • thyroiditis
  • excess iodine, a mineral important in the production of T4 and T3
  • a noncancerous tumor located at the base of the brain, although this is rare
  • too much thyroid hormone medication

Healthcare professionals use physical exams to assess whether somebody has any visible symptoms of a thyroid condition.

They may also ask for a personal and family history of health conditions, such as Hashimoto’s thyroiditis.

It is important for a person to disclose a full medical history, as well as if they have experienced any noticeable or rapid changes in weight.

To help them make a diagnosis, a doctor may order:

  • blood tests
  • ultrasound scan
  • thyroid scan
  • radioactive iodine uptake test
  • biopsy, if a lump is present on the thyroid

TSH levels

Healthcare professionals use blood tests to diagnose a thyroid condition. A doctor will send a blood sample to a lab for examination and testing.

A doctor may order the following blood tests:

  • TSH test: This test checks the amount of TSH in the blood. A high amount of TSH indicates hypothyroidism. Low TSH indicates hyperthyroidism.
  • T4 tests: High levels of T4 indicates that a person has hyperthyroidism. Low levels of T4 suggest hypothyroidism. However, abnormal levels of T4 can happen if a person is taking birth control pills or if they are pregnant. Some medications, such as corticosteroids, can also alter a person’s T4 levels.
  • T3 test: If a person’s T4 levels are normal, a T3 test can help confirm a diagnosis of hyperthyroidism.
  • Thyroid antibody tests: Measuring thyroid antibodies can help diagnose Graves’ disease and Hashimoto’s disease.

Treatment for thyroid conditions varies depending on the severity of the condition and the age of the person.


To treat hypothyroidism, a doctor prescribes medications to replace the thyroid hormones. They will usually prescribe levothyroxine in the form of a pill, liquid, or softgel capsule.

Before prescribing levothyroxine, a doctor will order a blood test to check thyroid levels, then repeat the blood test in 6–8 weeks after the medication is started.

The doctor will adjust the dose until a person reaches a dose that works for them. Each time the dose is adjusted, they will perform a blood test.


Treatment may include:

  • medications
  • radioiodine therapy
  • surgery

Medications include beta-blockers to reduce symptoms such as tremors or rapid heart rate.

Antithyroid medications, such as methimazole, or propylthiouracil for people in the first 3 months of pregnancy, can help the thyroid produce less hormones.

Radioiodine therapy is a common treatment for hyperthyroidism. It destroys the cells in the thyroid that are producing too much of the hormones.

People who take radioiodine therapy are likely to develop hypothyroidism. However, hypothyroidism is easier to treat and results in fewer complications.

Less often, a surgeon may remove a part, or most of, the thyroid gland. This can also result in hypothyroidism.

Hypothyroidism is a long lasting condition. Without treatment, hypothyroidism can cause severe complications, including coma or death.

However, with treatment, the outlook for people with hypothyroidism is good. Symptoms usually reverse within a few weeks or months.

Like hypothyroidism, hyperthyroidism can cause serious health problems without treatment. However, hyperthyroidism is treatable. A person’s outlook is typically positive.

If a person undergoes surgical treatment for hyperthyroidism, their condition will not return. However, they will have to take medications to treat the resulting hypothyroidism.

If a person believes they are experiencing any of the stated symptoms of thyroid conditions, they should reach out to a doctor.

A doctor may refer a person to see an endocrinologist, or hormone specialist.

The following are frequently asked questions about hypothyroidism and hyperthyroidism.

Do high levels of TSH indicate hypothyroidism or hyperthyroidism?

High levels of TSH can indicate hypothyroidism.

What is the difference between Hashimoto’s thyroiditis and hyperthyroidism?

Hashimoto’s thyroiditis is an autoimmune condition that causes the immune system to attack the thyroid gland. Hashimoto’s thyroiditis most commonly causes hypothyroidism.

In rare cases, Hashimoto’s thyroiditis can cause transient hyperthyroidism with subsequent hypothyroidism.

Hypothyroidism is a condition in which the thyroid is unable to produce enough thyroid hormones. Hyperthyroidism occurs when the thyroid produces too much of the thyroid hormones.

Too much of the thyroid hormones can speed up bodily functions, whereas low levels of the thyroid hormones can slow down bodily functions.

To diagnose each condition, a doctor will perform a physical examination and order blood tests and imaging tests.

Treatment involves leveling the levels of thyroid hormones. People typically have positive outlooks with treatment.