Hyperthyroidism, also known as overactive thyroid, occurs when the thyroid gland overproduces thyroid hormones, thus accelerating the body's natural functions. In contrast, hypothyroidism is the result of an underactive thyroid that is not secreting enough thyroid hormones, which leads to the slowing-down of natural functions.

Hypothyroidism is much more common than hyperthyroidism and is usually diagnosed by a blood test measuring the level of TSH (thyroid-stimulating hormone) in the body.

This comparison examines the causes (which can be varied), symptoms (which are often subtle and not obvious), diagnosis, and treatment options for hypothyroidism and hyperthyroidism.

Comparison chart

Hyperthyroidism versus Hypothyroidism comparison chart
Edit this comparison chartHyperthyroidismHypothyroidism
About Also known as overactive thyroid. Occurs when thyroid gland overproduces thyroid hormones, thus accelerating the body's natural functions. Also known as underactive thyroid. Occurs when thyroid glance is not secreting enough thyroid hormones, which leads to the slowing-down of the body's natural functions.
Most Common Cause Graves' disease, also known as toxic diffuse goiter Hashimoto's disease, also known as chronic lymphocytic thyroiditis
Other Causes Thyroiditis, iodine deficiency, medication, thyroid nodules. Thyroiditis, too much iodine, medication, genetics, hyperthyroidism treatments.
Diagnosis Thyroid-stimulating hormone (TSH) test, thyroid-stimulating immunoglobulin (TSI) test, thyroid scan, radioactive iodine uptake test. Thyroid-stimulating hormone (TSH) test, thyroid-stimulating immunoglobulin (TSI) test, thyroid scan, radioactive iodine uptake test.
Treatment Antithyroid medication (e.g., Methimazole) to slow overactive thyroid and, sometimes, beta blockers (e.g., Propranolol) to alleviate symptoms. Synthetic thyroid hormone (e.g., Levothyroxine) or carefully monitored iodine supplementation.
Occurrence Less common. Roughly 1% of U.S. has overactive thyroid. Women more likely to suffer due to effects of pregnancy. More common. Nearly 5% of U.S., could be as much as 20% if what is considered "normal" range is slightly adjusted. Women more likely to suffer due to effects of pregnancy.
Appetite Weight loss but increased appetite Weight gain but loss of appetite
Pulse Tachycardia Bradycardia
Skin Warm and moist Dry and coarse
Hair Fine and soft Thin and brittle
Temperature Intolerance Heat intolerance Cold intolerance
In Pets Occurs in about 2% of cats over 10 years of age and in 1-2% of dogs Can occur, but less common than hyperthyroidism
ICD-10 E05 E03.9
ICD-9 242.90 244.9
MedlinePlus 000356 000353
eMedicine med/1109 med/1145
DiseasesDB 6348 6558
MeSH D006980 D007037

What is the Thyroid?

The thyroid is an endocrine gland found in the neck of vertebrate animals, including humans. It stores, produces, and secretes hormones — triiodothyronine (T3) and thyroxine (T4) — into the bloodstream that regulate numerous functions, including heart rate and blood pressure, body temperature, metabolism, and the growth and development of the brain and nervous system. The brain's pituitary gland regulates the thyroid's hormone secretion with its own hormone known as the thyroid-stimulating hormone (TSH).

Causes of Thyroid Disorders

Other diseases can lead to the development of thyroid problems. In fact, nearly all overactive and underactive thyroid conditions in the U.S. are caused by two specific autoimmune diseases:

Other Causes

(Click to enlarge.) Iodine deficiency has become less common since the development of iodized table salt.
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(Click to enlarge.) Iodine deficiency has become less common since the development of iodized table salt.

Though most cases of hyperthyroidism and hypothyroidism are caused by Graves' and Hashimoto's, thyroid problems can be the result of other events, conditions, or circumstances:

Overactive vs. Underactive Thyroid Symptoms

Both hyperthyroidism and hypothyroidism can cause fatigue, hair loss/thinning, muscle or joint pain, mental anguish (e.g., anxiety and depression, mood swings, or irritability), and many other symptoms that are common to other diseases. Doctors must use other symptoms to evaluate the risk or presence of either disorder and cannot diagnose either without a blood test.

The most common signs and symptoms of hypothyroidism manifest in ways that suggest natural processes of the body are slowed or shutting down:

In contrast, the most common signs and symptoms of hyperthyroidism suggest natural processes are speeding up abnormally:

Diagnosis

A TSH test is often the first point of diagnosis that medical practitioners use. For this test, blood is drawn and tested for the presence of thyroid-stimulating hormone (TSH). A lab assigns a "normal" range for this hormone — usually between .5 and 4.5 mIU/L. If one's TSH levels fall outside of this normal range, it indicates hypothyroidism (anything above the normal range) or hyperthyroidism (anything below the normal range). It is worth noting that the American Association of Clinical Endocrinologists has recommended a smaller range of .3 to 3.0 mlU/L, which would make a much larger proportion of the U.S. population fall within the hypothyroid diagnosis.[1]

Those who are suspected to have hyperthyroidism may also have their T3 and T4 levels tested, as these levels are higher than normal in the case of hyperthyroidism. Furthermore, while a T3 test is not useful for the diagnosis of hypothyroidism, a lower than normal level of T4 indicates hypothyroidism.

A thyroid-stimulating immunoglobulin (TSI) test is used to check for a particular antibody associated with the Graves' and Hashimoto's diseases. This test helps narrow down the cause of hyperthyroidism and hypothyroidism, whether it is related to these autoimmune disorders or something else.

Two other tests are sometimes employed (and even used together): the thyroid scan and the radioactive iodine uptake test. The simplest thyroid scan, which makes use of ultrasound, is used to look for the presence of thyroid nodules, which can cause hyperthyroidism. More complex scans used for nuclear medicine are sometimes coupled with the radioactive iodine uptake test. For this test, radioactive iodine is injected into the bloodstream and later scanned to see how it has been used by the thyroid.

Treatment of Thyroid Disorders

There is no one cure for either disorder, and what treatment entails can vary from person to person due to the multiple causes of hyperthyroidism and hypothyroidism.

Even so, hypothyroidism is often controlled very well with the use of a synthetic thyroid hormone (e.g., Levothyroxine) or carefully monitored iodine supplementation. Those suffering from hyperthyroidism are typically prescribed an antithyroid medication (e.g., Methimazole) to slow the overactive thyroid and, sometimes, beta blockers (e.g., Propranolol) to alleviate symptoms.

For some, treating a thyroid disorder is a delicate balancing act. Unfortunately, overactive thyroid treatment — particularly more extreme forms of treatment, such as surgery — may eventually lead one to develop an underactive thyroid.

Occurrence

Roughly 1% of the U.S. population has hyperthyroidism. Hypothyroidism is much more common, affecting nearly 5% of the population that is 12 and older. If "normal" ranges for the thyroid-stimulating hormone were adjusted, as the American Association of Endocrinologists has recommended, around 20% of the population might be affected.[2]

Women are much more likely than men to suffer from either condition. Much of this is due to the effects of pregnancy. See also: thyroid disease in pregnancy.

Hyperthyroidism and Hypothyroidism In Animals

Animals may also suffer from an underactive or overactive thyroid. Hyperthyroidism is much more common in household pets, however, with about 2% of cats over 10 and 1-2% of dogs suffering from the disorder.[3][4]

References

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