Differences Between Hypothyroidism and Hyperthyroidism

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The thyroid gland is a butterfly-shaped organ that produces hormones. Two of these hormones, triiodothyronine (T3) and thyroxine (T4), regulate your metabolism, help your heart, brain, and other organs function, and have a major impact on almost every cell in your body.

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. This can cause body-wide symptoms.

When you have an underactive thyroid and it produces too little hormone, you have hypothyroidism. On the other hand, when you have an overactive thyroid and it produces too much hormone, you have hyperthyroidism. The causes, symptoms, and treatments differ between these two thyroid disorders.

What Is Autoimmunity?

Autoimmunity is a malfunction of the immune system. For reasons that aren’t yet understood, the immune system sometimes mistakes a healthy part of your body for a dangerous pathogen, like a virus, and launches an attack against it. The type of tissue(s) it targets varies by disease. More than 100 autoimmune diseases have been identified.

Woman performing a thyroid gland test

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Causes

Causes of Hypothyroidism
  • Autoimmune disease

  • Surgical removal

  • Radiation treatment

  • Congenital problem

  • Thyroiditis

  • Certain medications

  • Abnormal iodine levels

  • Pituitary gland damage

  • Rare diseases

Causes of Hyperthyroidism
  • Autoimmune disease

  • Nodules

  • Thyroiditis (temporary)

  • Overmedication

  • Abnormal iodine levels

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 Cordarone or Pacerone (amiodarone), Eskalith or Lithobid (lithium), Intron A or Roferon-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.

The Role of Iodine

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.

Symptoms

Symptoms of Hypothyroidism
  • Fatigue

  • Weight gain

  • Feeling extra cold

  • Constipation

  • Hair loss

  • Decrease in sweating

  • Heavy and irregular periods

  • Slow heart rate

  • Brittle nails

  • Irritability and depression

  • Puffy face

  • Muscle or joint pain

  • Insomnia

Symptoms of Hyperthyroidism
  • Fatigue

  • Weight loss or gain

  • Feeling extra warm

  • Diarrhea

  • Hair loss

  • Increased sweating

  • Light and short periods

  • Racing or pounding heart

  • Nail thickening, flaking

  • Anxiety and nervousness

  • Bulging or puffy eyes

  • Muscle weakness

  • Insomnia

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. You may feel tired and sluggish, your heart rate drops, you feel cold even when people around you are warm, and you gain weight. You also tire easily with exercise. Changes to your digestion can lead to constipation.

Your blood flow, water retention, and cellular replacement may decrease as well, affecting the health of your skin, hair, and nails. Your face and hands may appear puffy. You may also feel confused and find it difficult to focus, causing what's known as brain fog.

It may become difficult to conceive, and the risk of miscarriage is higher for people with a hypoactive thyroid. Your period may be irregular or it may skip frequently. Fertility treatments may be ineffective. Hypothyroidism also can cause erectile dysfunction, difficulty ejaculating, and a decreased sex drive.

Hyperthyroidism Symptoms

When you have an overactive thyroid, your body and its processes are sped up. Many of the symptoms are the opposite of hypothyroidism symptoms, such as feeling hotter than is typical for the environment.

Your heart may race and develop irregular rhythms. You may have high blood pressure. A rise in blood flow to your cells can make your skin unusually smooth and soften your fingernails. Food may go right through you as your digestive system speeds up, leading to poor absorption of some nutrients. You can end up with diarrhea or frequent bowel movements.

Initially, this can give you extra energy. However, it's short-lived. Your body isn't meant to maintain this fast pace, so you'll eventually become fatigued.

Complications

Hypothyroidism Complications
  • Goiter

  • Pregnancy problems

  • Peripheral neuropathy

  • Anemia

  • High cholesterol

  • Muscle disease

  • Myxedema coma

Hyperthyroidism Complications
  • Goiter

  • Pregnancy problems

  • Neonatal hyperthyroidism

  • Osteoporosis

  • Atrial fibrillation

  • Thyroid storm

Hypothyroidism Complications

If hypothyroidism remains untreated or undertreated, it may lead to some unpleasant 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.

Treatments

Hypothyroidism Treatments
  • Thyroxine (T4) replacement

  • Sometimes, added T3 replacement

Hyperthyroidism Treatments
  • Antithyroid drugs

  • Radioactive iodine

  • Beta-blocker drugs

  • Surgical removal of the thyroid

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.

Some people who are still symptomatic on thyroxine replacement medications may be given T3 replacement hormones in addition to T4 replacement therapy.

Myxedema coma 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 the 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 Tapazole (methimazole), 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:

After any of those treatments, it's possible for the 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:

Diet for Thyroid Health

To help protect your thyroid health, you should avoid or limit:

  • Inflammatory foods
  • Foods that spike your blood sugar levels
  • Unhealthy fats
  • Table salt
  • Sweets
  • Caffeine
  • Alcohol
  • Goitrogens (foods that slow your thyroid gland and promote goiter), including raw kale, spinach, broccoli, cauliflower, Brussels sprouts, peanuts, strawberries, and peaches

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

Hypothyroidism and hyperthyroidism are common diseases. While each condition has different symptoms and complications that can interfere with your quality of life and a few that are potentially life-threatening, most people with thyroid disease can manage their condition with current medications or medical procedures.

If you suspect you have an undiagnosed thyroid disease or that your thyroid disease could be better treated, talk to your healthcare provider. They should be able to guide you toward treatment options that can help you keep your condition under control.

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8 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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