Underactive or Overactive Thyroid What's the Difference

March 10, 2021

3 min read

Your thyroid is a butterfly-shaped gland found at the base and front of your neck. It works as a control center for your body. Your thyroid secretes hormones that help maintain heart, muscles, brain, and other organs and assist your body in using energy properly.

Therefore, when something goes wrong and causes an underactive or overactive thyroid, your metabolism either slows way down or speeds up too high, respectively. These two conditions — underactive thyroid (hypothyroidism) and overactive thyroid (hyperthyroidism) impact your thyroid in various ways and therefore have distinct symptoms.

The Difference Between Underactive and Overactive Thyroid

The biggest difference between the two conditions is the hormone output of the thyroid. In simple terms, with hyperthyroidism, your thyroid is making too much of the thyroid hormone your body needs and with hypothyroidism, it's not making enough.

Around 20 million people in the U.S. have some type of thyroid disease, according to the American Thyroid Association, but up to 60% of these people that have the condition, aren't even aware of it. Autoimmune diseases, like Graves' disease and Hashimoto's disease, are among the most common culprits of these two conditions, respectively.

Underactive Thyroid (Hypothyroidism)

Hypothyroidism is where your thyroid is underactive and doesn't produce enough.

Symptoms of Hypothyroidism

Common hypothyroidism symptoms are:

Weight gain
Constipation
Forgetfulness
Cold sensitivity
Dry skin
Fatigue

Causes of Hypothyroidism

The most common cause of underactive thyroid in the U.S. is Hashimoto's thyroiditis. Other causes of the condition are:

Past radiation for neck and head cancer
Past surgical treatment or radioiodine for thyroid cancer, hyperthyroidism, or another thyroid disease
Medications like lithium, amiodarone (Pacerone), and anti-epilepsy drugs
Congenital hypothyroidism or Hypothyroidism present at birth

Treatment for Hypothyroidism

Synthroid (Levothyroxine sodium tablets) can be taken once daily as a replacement hormone for helping to regulate your thyroid levels. They contain a synthetic hormone that's the same as thyroxine, which is the hormone your thyroid gland naturally produces.

Typically, you must take thyroid replacement medicine for life since hypothyroidism's effects are irreversible.

Overactive Thyroid (Hyperthyroidism)

Hyperthyroidism is an overactive thyroid that produces too much of the thyroid hormone.

Symptoms of Hyperthyroidism

Symptoms of hyperthyroidism are:

Brittle skin
Weight loss
Hand tremor
Irritability
Fast heart rate
Nervousness
Muscle weakness
Trouble sleeping
Less frequent or weaker periods

Causes of Hyperthyroidism

The most common cause of this condition is Graves' disease. Other causes of hyperthyroidism are:

Postpartum thyroiditis (following giving birth)
Small masses in the thyroid (referred to as toxic nodular goiters)
Taking too much thyroid hormone
Thyroiditis (inflammation of your thyroid because of a virus)

Treatment for Hyperthyroidism

Propylthiouracil (PTU) or Methimazole are used for treating hyperthyroidism. They signal your thyroid to slow T3 and T4 hormone production down. They come in tablet form and might be taken up to three times daily. Like with hypothyroidism treatment, this isn't a cure.

Foundations and Societies

American Thyroid Association: The ATA is committed to transforming thyroid care through education, clinical excellence, advocacy, and scientific discovery in a collaborative community.
Graves' Disease & Thyroid Foundation: Established in 1990, this organization is the top source of hope and help for individuals with thyroid-related disorders like Graves' disease.
ThyCa: Thyroid Cancer Survivors' Association, Inc.: Thyroid cancer survivors created and maintain this website.

Latest Insights on Underactive and Overactive Thyroid

New insights in the treatment of hypothyroidism reveal that personalized medicine might be able to be an effective treatment in all patients.

Several novel therapeutic options specifically for Graves’ patients may be clinically available in the future that restores a patient's euthyroid state without requiring ongoing therapy.

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