How to Tell the Difference Between Hyperthyroidism and Hypothyroidism

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. Although both share many of the symptoms, there are certain symptoms distinctive of each.

Both hyperthyroidism and hypothyroidism are largely the result of an autoimmune disease, but there are other potential causes as well. The diagnosis and treatment also differ.

What Is Hyperthyroidism?

Hyperthyroidism occurs when the butterfly-shaped organ in the neck called the thyroid gland produces excessive amounts of thyroid hormones known as triiodothyronine (T3) and tetraiodothyronine (T4). These hormones, composed largely of iodine, help regulate many body functions, including growth, heart rate, and metabolism (the conversion of calories into energy).

Hyperthyroidism may involve the thyroid gland itself or a pea-sized organ in the brain called the pituitary gland which directs the secretion of T3 and T4.

Symptoms

The overproduction of T3 and T4 can cause an array of symptoms affecting your hair, weight, digestion, heart rate, energy levels, moods, body temperature, and menstrual cycle.

Common signs and symptoms of hyperthyroidism include:

• Fatigue
• Weight loss or gain
• Feeling constantly warm
• Puffy hands and face
  
• An enlarged thyroid gland (goiter)
• Diarrhea
• Hair loss
• Increased sweating
• Short or light periods
• Racing or pounding heart
• Nail thickening or flaking
• Anxiety and nervousness
• Muscle weakness
• Insomnia

Causes

Hyperthyroidism can be due to conditions that cause thyroid inflammation (referred to as thyroiditis) or the development of nodules that secrete T3 and T4 irrespective of the pituitary gland.

Common causes of hyperthyroidism include:

• Graves' disease: An autoimmune disease that accounts for the majority of hyperthyroid cases
• Thyroid adenoma: A benign tumor on the thyroid gland
• Pituitary adenoma: A benign tumor of the pituitary gland
• De Quervain's thyroiditis: A mild form of hyperthyroidism that tends to resolve on its own
• Postpartum thyroiditis: A transient form of hyperthyroidism that occurs soon after pregnancy
• Amiodarone: A drug similar in structure to T4 used to treat abnormal heartbeats (arrhythmia)
• Excess iodine consumption: Most notably from algae such as kelp
• Overuse of thyroid hormones: Used to treat people with hypothyroidism
  

What Is Hypothyroidism?

Hypothyroidism occurs when the body doesn't produce enough thyroid hormones. It involves conditions that damage the thyroid gland itself (called primary hypothyroidism), the pituitary gland (called secondary hypothyroidism), or a part of the brain that stimulates the pituitary gland called the hypothalamus (called tertiary hypothyroidism).

Symptoms

The underproduction of T3 and T4 can also cause symptoms affecting your hair, weight, digestion, heart rate, energy levels, moods, body temperature, and menstrual cycle, often in significantly different ways to hyperthyroidism.

Common signs and symptoms of hypothyroidism include:

• Fatigue
• Weight gain
• Feeling constantly cold
• Puffy face
• Goiter
  
• Constipation
• Hair loss
• Lack of sweating and dry skin
• Heavy or irregular periods
• Slowed heart rate
• Brittle nails
• Depression and irritability
• Muscle and joint aches
• Insomnia

Causes

Primary hypothyroidism is about a thousand times more common than secondary and tertiary hypothyroidism. Some of the same conditions that cause hyperthyroidism can also cause hypothyroidism.

Primary causes of hypothyroidism include:

• Hashimoto’s disease: An autoimmune disease that accounts for most hypothyroid cases
• Iodine deficiency: More common in poorer countries with widespread nutritional deficiency
• Thyroidectomy: The surgical removal of the thyroid gland, often due to thyroid cancer
• Neck radiation: Often used to treat head and neck cancers or Graves' disease
• Medications: Including amiodarone, lithium, and interferon-alpha
• Thyroid dysgenesis: A birth defect that causes a missing or partially missing thyroid gland
• Acute infectious thyroiditis: Caused by bacterial infections like strep throat in children
• Postpartum thyroiditis: Sometimes causes thyroid hormones to drop after pregnancy
• Thyroid sarcoidosis: A disease that can cause granular deposits in the thyroid gland
• Amyloidosis goiter: The enlargement of the thyroid gland due to deposits of amyloid proteins
• Hemochromatosis: The overload of iron which can affect the thyroid gland, more often in men

Secondary and tertiary causes of hypothyroidism include:

• Pituitary adenoma: Sometimes causes T3 and T4 levels to drop instead of rise
• Pituitary surgery: Used to remove pituitary adenomas and other tumors
• Brain radiation: Commonly used for the treatment of secondary brain cancer
• Autoimmune hypophysitis: A rare autoimmune disease of the pituitary gland
• Lymphocytic adenohypophysis (LAH): A rare pituitary condition that develops after pregnancy
• Vascular diseases: Involving the internal carotid artery servicing the pituitary and hypothalamus
• Medications: Including the long-term use of opioid drugs

Complications

When hyperthyroidism and hypothyroidism are left untreated, they can lead to complications, some of which may be serious. These complications involve many of the same organ systems but often in very different ways.

Hyperthyroidism

Complications of untreated hyperthyroidism include:

• Proptosis: The prominent bulging of the eyes, also known as exophthalmos
• Graves' ophthalmopathy: An eye complication characterized by watery eyes, blurred vision, and double vision
• Osteoporosis: Porous, brittle bones caused by the loss of bone mineral
• Atrial fibrillation: A heart condition that causes an irregular and abnormally fast heartbeats
• Pregnancy complications: Including premature birth, low birth weight, preeclampsia, and miscarriage
• Thyroid storm: A potentially life-threatening condition caused by dramatic increases in metabolism, leading to confusion, vomiting, extremely fast heartbeats, and liver injury

Babies born to mothers with Graves' disease are also at increased risk of developing hyperthyroidism.

Hypothyroidism

Complications of untreated hypothyroidism include:

• Anemia: Low red blood cells caused by suppression of bone marrow
• Loss of fertility: Due primarily to abnormal periods
• Peripheral neuropathy: Burning or tingling sensations caused by damage to nerve membranes
  
• Congestive heart failure: The inability of the heart to enough blood to service the body's needs
• Pregnancy complications: Including premature birth, low birth weight, preeclampsia, miscarriage, placental abruption, and postpartum hemorrhage (bleeding)
• Myxoedema coma: A potentially life-threatening condition caused when thyroid hormone levels become exceptionally low, leading to confusion, low body temperature, drowsiness, and coma
  

Diagnosis

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

This includes measuring your T4 hormone levels as well as a hormone produced by the pituitary gland called thyroid-stimulating hormone (TSH) that tells the thyroid gland when to secrete T3 and T4.

Based on the results of the TSH and T4 tests:

• Hypothyroidism is indicated with a TSH over 4.0 milli-international units per liter (miU/L) and a T4 under 5.0 mIU/L.
• Hyperthyroidism is indicated with a TSH under 0.4 mIU/L and a T4 over 11.0 mIU/L. T3 blood tests over 200 nanograms per deciliter (ng/dL) may help confirm the diagnosis.

Thyroid antibody tests may help diagnose autoimmune hyperthyroidism, either in the form of Graves' disease or Hashimoto's disease.

Treatment

The treatments for hyperthyroidism are different from those for hypothyroidism. One aims to stem the production of T3 and T4, while the other aims to replace thyroid hormones with synthetic or natural thyroid hormones.

Hyperthyroidism

Medications, radiation, surgery, or a combination of treatments may be prescribed to treat hyperthyroidism. This may include:

• Anti-thyroid medicine: Typically a drug called Tapazole (methimazole) which stops the thyroid gland from making too many hormones
• Radioiodine therapy: Involving an infusion of radioactive iodine which the thyroid gland takes up, causing it to shrink
• Beta-blockers: Including drugs like Inderal (propranolol) and Lopressor (metoprolol) which lessen symptoms of hyperthyroidism, such as tremors, rapid heart rate, and palpitations
• Thyroidectomy: A surgery less commonly used today which involves the removal of part of or all of the thyroid gland 

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

Hypothyroidism

The treatment of hypothyroidism is focused on replacing T4 with a biologically equivalent thyroid hormone called levothyroxine (marketed under the brand name Synthroid, Levo-T, and others). Taken daily, it can start to normalize thyroid hormone levels within one to two weeks.

Generally speaking, you won't need a bioequivalent form of T3, called Cytomel (liothyronine), because T4 is naturally converted in the body into T3. Even so, some providers will add Cytomel to the treatment plan if you have not had success taking T4 on its own or are still struggling with thyroid symptoms.

Though not endorsed as part of standard hypothyroid care, a natural hormone product called Armour Thyroid (desiccated thyroid) derived from pigs has been used for generations to treat hypothyroidism.

Summary

Hyperthyroidism is an overactive thyroid gland, and hypothyroidism is an underactive thyroid gland. The main cause of each is autoimmune thyroid disease (respectively, Graves' disease and Hashimoto's disease). Hyperthyroid treatment is based on slowing thyroid hormone production, while hypothyroid treatment involves hormone replacement therapy.

Both can cause fatigue, hair loss, and pregnancy complications, but hyperthyroidism is more likely to cause diarrhea, rapid heartbeats, increased sweating, anxiety, and sensitivity to heat. Hypothyroidism, on the other hand, is more likely to cause constipation, slowed heartbeats, reduced sweating, depression, and sensitivity to heat.

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