Hyperthyroidism vs. Hypothyroidism: Differences and Symptoms

Hyperthyroidism is an overactive thyroid gland that produces too much thyroid hormone while hypothyroidism is an underactive thyroid gland that produces too little thyroid hormone.

Hypothyroidism is more common than hyperthyroidism. Both conditions can be caused by an autoimmune disease, though there are other potential causes.

Symptoms of hyperthyroidism include weight loss, increased metabolism, irregular heartbeat, nervousness, and irritability. Symptoms of hypothyroidism include weight gain, fatigue, dry skin, and sensitivity to cold.

This article explores the many symptoms, causes, complications, and treatments of hypothyroidism vs. hyperthyroidism.

What Does Your Thyroid Do?

The thyroid gland is a butterfly-shaped organ located at the front of the neck under the voice box. The thyroid regulates many body functions by releasing the right amount of thyroid hormones.

The thyroid makes two hormones: triiodothyronine (T3) and tetraiodothyronine (T4). These hormones regulate body temperature, heartbeat, metabolism, brain and organ function, and growth and development.

The thyroid is regulated by the pituitary gland in the brain. This gland produces a hormone called thyroid-stimulating hormone (TSH) to tell the thyroid to make more T3 and T4. When any part of this system is damaged or malfunctioning, the thyroid can produce either too little or too much T3 and T4.

Symptoms of Hyperthyroidism vs. Hypothyroidism

The early warning signs of thyroid problems can be easy to mistake for other health conditions. Fatigue, for example, is often experienced by people in menopause. There are a few symptoms, however, that taken together can alert you that it’s time to see a healthcare provider:

• Fatigue, or tiredness that doesn’t go away after a good night’s sleep
• Weight loss or gain
• Your resting heart rate speeds up or slows down
• You’re more sensitive to hot or cold temperatures
  

Hypothyroidism Symptoms

Because thyroid hormones regulate your metabolism, having an underactive thyroid slows down your body’s processes, and that causes a wide array of symptoms, such as:

• Feeling tired and sluggish
• Lower heart rate
• Feeling cold even when people around you are warm
• Weight gain
• Puffy hands and face
• Tire easily with exercise
• Constipation
• Confusion or difficulty focusing
• Irregular periods

It may also be difficult to conceive, and the risk of miscarriage is higher for people with an underactive thyroid. Fertility treatments may be ineffective.

Hypothyroidism can also cause erectile dysfunction, difficulty ejaculating, and a decreased sex drive.

Hyperthyroidism Symptoms

When you have an overactive thyroid, your body and its processes speed up. Many of the symptoms are the opposite of hypothyroidism symptoms, such as:

• Feeling hotter than is typical for the environment
• Racing heart or irregular heartbeat
• High blood pressure
• Unusually smooth skin and soft fingernails
• Diarrhea or frequent bowel movements

Initially, hyperthyroidism can give you extra energy, but the body isn’t meant to maintain this fast pace, so eventually fatigue sets in.

Causes of Thyroid Disease

Thyroid disease is common. In the United States, it affects an estimated 20 million people. Up to 60% of those who have thyroid disease are undiagnosed.

Hypothyroidism Causes

Possible causes of hypothyroidism include:

• Autoimmune disease: This includes Hashimoto’s disease and atrophic thyroiditis. They’re the most common causes of a hypoactive thyroid.
• Surgical removal: Sometimes all or part of the thyroid gland is removed as a treatment for thyroid cancer, thyroid nodules, or Graves’ disease.
• Radiation treatment: This treatment for certain cancers, Graves’ disease, and thyroid nodules can damage the thyroid gland and impair its function.
• Congenital problem: Rarely, a baby is born with a partial or missing thyroid gland or other abnormalities that impair thyroid function.
• Thyroiditis: This is inflammation of the thyroid caused by viral infection or atrophic thyroiditis.
• Certain medications: In people with a genetic predisposition, drugs that may trigger hypothyroidism include Pacerone (amiodarone), Lithobid (lithium), Intron A (interferon α), Proleukin (aldesleukin or interleukin-2), and checkpoint inhibitors like Yervoy (ipilimumab).
• Abnormal iodine levels: Iodine is a crucial component of thyroid hormones, so if your body doesn’t get enough from the foods you eat, it can’t keep thyroid hormones in balance.
• Pituitary gland damage: If it’s damaged by a tumor, radiation therapy, or surgery, the pituitary gland’s control over the thyroid may be impaired and lead to a deficiency of thyroid hormones.
• Rare disorders: These include amyloidosis, sarcoidosis, and hemochromatosis. Each one deposits substances in the thyroid that shouldn’t be there and can impair its function as a result.
  

Hyperthyroidism Causes

Hyperactive thyroid has fewer potential causes. It may run in families. Other causes include:

• Autoimmune disease: Graves’ disease is behind more than 70% of hyperactive thyroid cases. Damage to the thyroid is caused by antibodies that chronically activate the thyroid and lead to hormone overproduction.
• Nodules: Abnormal growths of thyroid tissues can lead to excess hormone secretion.
• Thyroiditis: When thyroiditis first strikes, it can cause the thyroid to release all the hormones it has produced, leading to temporary hyperthyroidism. After that, levels drop into the hypothyroid range.
• Overmedication: If you take too much thyroid hormone medication for hypothyroidism, it can lead to hyperthyroidism.
• Abnormal iodine levels: If you’re iodine deficient and suddenly increase your iodine intake, you may develop temporary hyperthyroidism while your body adjusts to the change.

Iodine is an element your body can’t make on its own, so you depend on food to get enough of it. Thyroid cells absorb iodine from your bloodstream and use it to create T3 and T4. Low iodine levels can lead to hypothyroidism, and excess iodine in your blood can lead to hypothyroidism or hyperthyroidism.

Possible Complications

When hypothyroidism or hyperthyroidism are untreated or undertreated, it can lead to complications.

Hypothyroidism Complications

• Goiter: An enlarged thyroid gland may feel like a lump in your throat. Large goiters may be tender and swollen, and neckties and scarves may be uncomfortable to wear. In rare cases, goiters can make it difficult to swallow or breathe.
• Pregnancy problems: Irregular menstrual cycles can lead to infertility. Additionally, hypothyroidism increases the risk of miscarriage, placental abruption, early delivery, and death of the baby.
• Peripheral neuropathy: Nerve damage, potentially from fluid retention and swelling, leads to numbness, tingling sensations, weakness, and hypersensitivity to touch or temperature.
• Anemia: Thyroid hormone deficiency impairs your bone marrow's production of red blood cells, leading to anemia. Symptoms include fatigue, pale skin, fast or irregular heartbeat, feeling faint, and shortness of breath.
• High cholesterol: Your body is unable to process cholesterol properly, which can cause high levels of LDL and total cholesterol.
• Muscle disease: Muscle pain and stiffness, possibly accompanied by muscle weakness, can have a major impact on your functionality and daily life.
• Myxedema coma: This is a rare and potentially fatal consequence of severe hypothyroidism triggered by infection, heart problems, or other physical stressors. Symptoms include low body temperature and blood pressure, slow heart rate, and being unresponsive due to poor function of multiple organs.

Hyperthyroidism Complications

• Goiter: As in hypothyroidism, a goiter causes the feeling of a lump in your throat, may be painful, and may impair swallowing or breathing.
• Pregnancy problems: Moderate-to-severe hyperthyroidism can lead to preeclampsia, early delivery, small babies, stillbirth, and possibly birth defects.
• Neonatal hyperthyroidism: When the person carrying a baby has Graves' disease, their infant may be born with hyperthyroidism or even develop it before birth. This can cause low birth weight, unusually small heads, fast heartbeat, irritability, poor sleep, and rarely, a dangerous accumulation of fluid (fetal hydrops).
• Osteoporosis: Weak bones make you more prone to fractures.
• Atrial fibrillation: This abnormal heart rhythm can lead to heart failure or stroke.
• Thyroid storm: This rare but potentially deadly condition can be triggered by a combination of untreated hyperthyroidism and infection, surgery, or trauma. It includes an extremely fast heart rate, high fever, agitation, diarrhea, delirium, and possibly decreased consciousness.

Diagnosing Hypothyroidism and Hyperthyroidism

For both conditions, a healthcare provider will take a medical history, do a physical exam and order one or more blood tests to check thyroid function.

Hypothyroidism is associated with TSH > 4.0 milli-international units per liter (miU/L) and T4 < 5.0 mIU/L.

Hyperthyroidism is associated with TSH < 0.4 mIU/L and T4 > 11.0 mIU/L. Blood levels of T3 may also be tested to confirm a diagnosis of hyperthyroidism if T3 is > 200 nanograms per deciliter (ng/dL).

Thyroid antibody tests may help diagnose an autoimmune disorder that may be causing hyperthyroidism (like Graves' disease) or hypothyroidism (like Hashimoto's disease).

Note that normal lab reference ranges can vary slightly and some healthcare providers will order free T4 and free T3 to get more accurate measurements.

Treating Hypothyroidism and Hyperthyroidism

The treatment options will depend on which condition you have and what is causing it.

Hypothyroidism Treatments

While hypothyroidism can’t be cured, it can be managed with the appropriate treatment. The primary treatment for a hypoactive thyroid is synthetic thyroxine taken in pill form. It works just like your natural thyroxine and helps restore proper function to your organs and systems.

People who are still symptomatic when taking synthetic thyroxine may be inefficiently converting T4 (synthetic thyroxine) to the active hormone T3. Thus, they may be given T3 replacement hormones in addition to T4 replacement therapy.

Myxedema coma (a rare, life-threatening condition caused by long-term untreated hypothyroidism) is treated with T4, possibly T3, and some combination of:

• Hydrocortisone
• Intubation and mechanical ventilation
• Gentle warming
• Fluid restriction
• Increased blood volume
• Glucose
• Antibiotics, if an infection is an underlying cause

Hyperthyroidism Treatments

Hyperthyroidism is highly treatable, and between 20% and 30% of people with Graves’ disease may enter into long-term remission with treatment.

Antithyroid drugs, usually methimazole (previously marketed as Tapazole), can block your thyroid’s ability to make hormones and therefore control the disease without damaging the gland itself. These drugs may be taken before radioactive iodine or surgery for people with nodules.

Radioactive iodine, taken by mouth, damages or destroys thyroid cells, thereby leaving fewer cells to produce thyroid hormones and shrinking nodules. This lowers hormone levels to the desired range. If the first treatment isn’t successful enough, a second course may be given. Sometimes this treatment results in hypothyroidism, which is then treated with replacement hormones.

Treatment with radioactive iodine is extremely common. Some people worry that the radiation may cause cancer, but the treatment hasn’t been linked to increased cancer rates.

Beta-blockers won’t lower your thyroid hormone levels, but they can block the actions of the hormones and alleviate symptoms. These medications include:

• Inderal (propranolol)
• Tenormin (atenolol)
• Lopressor (metoprolol)
• Corgard (nadolol)

After any of those treatments, it’s possible for hyperthyroidism to return. However, surgical removal of all or most of the thyroid gland can cure the condition permanently. It may lead to hypothyroidism because few or no cells are left to produce hormones, so thyroid replacement hormones will be necessary for the rest of your life if you opt to have your thyroid removed.

While it’s generally considered safe, surgery always carries risks. Major complications are rare but can include:

• Damage to the parathyroid glands, which control calcium levels in your body
• Damage to the nerves of your vocal cords, which leads to a hoarse voice

Summary

Your thyroid can produce too much or too little of the hormones that are essential to normal bodily function. Each has different causes, symptoms, and treatment.

However, since thyroid hormones regulate your metabolism, both conditions can affect many parts of your body.

A Word From Verywell

Thyroid disease is common, and both hypothyroidism and hyperthyroidism have different symptoms and complications. Most people with thyroid disease can manage their condition with medication or medical procedures. If you suspect you have undiagnosed thyroid disease or that your thyroid disease could be better treated, talk to your healthcare provider.

— ISABEL CASIMIRO, MD, PHD, MEDICAL EXPERT BOARD