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Hyperthyroidism, or overactive thyroid gland, is a condition in which the thyroid gland makes more thyroid hormones than are needed by your body. 

Prevalence and Risk Factors

Approximately 1.2% of the American population has hyperthyroidism. It is more common in women and people over the age of 60. Other risk factors for developing symptoms of hyperthyroidism include:

• A family history of thyroid disorders.

• Medical conditions such as vitamin B12 deficiency, type 1 diabetes, and primary adrenal insufficiency.

• A high-iodine diet (such as eating large amounts of seaweed).

• Use of nicotine products.

• Thyroid surgery 

• Use of certain prescription medications, such as amiodarone. 

• Pregnancy within the last 6 months (postpartum thyroiditis).

The Thyroid Gland and Thyroid Hormones: What is Their Role in Your Body?

The thyroid gland is a small butterfly-shaped gland in the front of your neck. It is an endocrine gland that makes and secretes two thyroid hormones - thyroxine or tetraiodothyronine (T4) and triiodothyronine (T3). These hormones control many important functions and affect nearly every organ system in the body. Thyroid hormones influence breathing, heart rate, metabolism, digestion, and mood. Thyroid hormones are also necessary for normal growth in children. Changes in the levels of these hormones can cause thyroid disease.

Overactive thyroid cells produce excess thyroid hormone, which can cause the body’s metabolism to speed up. Without treatment, hyperthyroidism can cause serious health complications in the heart, muscles, bones, menstrual cycle, and fertility.

Key Distinctions Between Hyperthyroidism and Hypothyroidism

Hyperthyroidism is an overactive thyroid gland with too much thyroid hormone. Hypothyroidism is an underactive thyroid gland with less thyroid hormone than the body requires. Hypothyroidism is more common than hyperthyroidism in the U.S.

While  some of the symptoms of hypo- and hyperthyroidism can overlap, their causes and treatments are very different. Hyperthyroidism is treated with antithyroid medicine to reduce the amount of thyroid hormones in the body. Hypothyroidism is treated with thyroid hormone medicine to replace thyroid hormones. 

Learn more about hypothyroidism vs hyperthyroidism.

Causes and Types of Hyperthyroidism

There are several different causes of hyperthyroidism, including autoimmune disorders, infections, excess iodine, and pregnancy. The three main types are briefly explained below.

Graves' Disease: The Most Common Culprit

Graves’ disease, also called toxic diffuse goiter, is an autoimmune disorder. It occurs when the body’s immune system creates too many thyroid stimulators, leading to an overproduction of thyroid hormones. Graves’ disease is the most common cause of hyperthyroidism. 

Thyroid Nodules and Their Impact

Thyroid nodules are small growths in the thyroid gland. Also called toxic nodular goiter, they are usually benign (not cancer). Overactive thyroid nodules can lead to the production of too much thyroid hormone. They are more common in older individuals.

Other Causes: Thyroiditis and Thyroid Storm

Thyroiditis is an inflammation of the thyroid gland. It can occur due to an infection or autoimmune condition. Thyroiditis can cause both hypothyroidism and hyperthyroidism. Thyroiditis can damage thyroid cells causing the thyroid hormones to be leaked into your blood and, as a result, increase thyroid hormone levels. 

Other possible causes of hyperthyroidism include:

• Excess iodine intake (iodine is found in certain medications, supplements, and seaweed)

• Too much thyroid medicine (higher doses of levothyroxine for hypothyroidism treatment) (Learn more about levothyroxine dosing)

• Hyperfunctioning thyroid tumors (benign or malignant)

• Conditions that affect the pituitary gland or hypothalamus, which are parts of the brain that regulate thyroid hormone secretion by the thyroid gland

Though extremely rare, thyroid storm is a life-threatening complication. While the exact causes are unclear, long-term untreated or undertreated hyperthyroidism can develop into thyroid storms. 

Other contributing factors of thyroid storms are trauma, infection, diabetic ketoacidosis (DKA), heart failure, stroke, abrupt stop of antithyroid medication, imaging procedures using iodinated contrast agent, and giving birth. 

Thyroid storm is associated with dangerously high heart rate, blood pressure, and body temperature due to too much thyroid hormone. Thyroid storms require prompt treatment in the hospital or it can be fatal.

Symptoms, Diagnosis, and Severity

Identifying Symptoms of Hyperthyroidism (Too Much Thyroid Hormone)

The National Institute of Diabetes and Digestive and Kidney Diseases lists the following symptoms of hyperthyroidism:

• Fatigue

• Muscle weakness

• Mood swings

• Nervousness and irritability

• Heat intolerance and/or excessive sweating

• Trouble sleeping

• Tremor (shaky hands)

• Rapid, irregular heartbeat

• Diarrhea or frequent bowel movements

• Weight loss

• Enlarged thyroid gland (goiter), which can cause problems with breathing and swallowing

Check out eight signs you may have a thyroid condition.

Understanding Blood Tests: TSH, FT3, and Thyroxine Levels

Thyroid blood tests are used to diagnose thyroid disease (both hypothyroidism and hyperthyroidism). These tests include TSH, T3 and T4, and thyroid antibodies.

• Thyroid-stimulating hormone (TSH) is a hormone made by the pituitary gland in the brain that stimulates the thyroid gland to produce thyroid hormones T3 and T4. A low TSH indicates that your thyroid gland is producing too much thyroid hormone. 

• T3 (triiodothyronine) and T4 (thyroxine/tetraiodothyronine ) blood tests measure the two main thyroid hormone levels in your blood. Hyperthyroidism patients typically have high T3 and T4 levels.

• Thyroid antibody tests look for thyroid antibodies in your blood. The presence of these antibodies might indicate an autoimmune disorder such as Graves’ disease (hyperthyroidism) or Hashimoto’s thyroiditis (a common cause of hypothyroidism). 

In addition to blood tests, your doctor will also obtain a medical history and perform a physical exam. You may also need to undergo imaging tests such as a thyroid ultrasound, thyroid scan, or radioactive iodine uptake test to have hyperthyroidism diagnosed and the cause identified.

What Constitutes a "Bad" Number for Hyperthyroidism?

TSH levels below 0.4 milli-international units per liter (mIU/L) indicate hyperthyroidism.

Normal thyroid blood test values are as follows:

• TSH: 0.5 to 5.0 mIU/L

• Total T4: 5 to 12 micrograms per deciliter (mcg/dL)

• Free T4: 0.7 to 1.9 nanograms per deciliter (ng/dL)

• Total T3: 80 to 220 ng/dL

Notably, free T3 assays are often unreliable. Therefore, it is not used in routine blood work to assess thyroid function. The normal ranges of thyroid hormone tests may vary among different laboratories. 

Are the ranges of thyroid hormone levels the same for everyone?

Different people may have other goals for thyroid hormone levels, and your doctor will help determine your goal ranges. For example, seizure medications (such as phenytoin, carbamazepine, and phenobarbital) and rifampin (an antibiotic) can increase the breakdown of thyroid hormones; as a result, you may have different optimal ranges of thyroid hormone levels. 

Additionally, pregnancy, history of thyroid cancer, liver disease, and pituitary gland disease are some other instances where the optimal ranges of thyroid hormone levels may be different than those listed above. 

Your healthcare team will adjust your medication dosage to ensure your thyroid disorder is optimally managed. Talk to your doctor if you have questions about different factors that can affect your thyroid hormone levels. 

Differentiating Between Mild and Severe Hyperthyroidism

Low but detectable TSH levels between 0.1 to 0.4 mIU/L with normal thyroid hormone levels (T3 and T4) indicate mild or early hyperthyroidism. Approximately 3 out of 4 people with hyperthyroidism fall in this category. Some people may have subclinical hyperthyroidism, meaning low TSH, but normal thyroid hormone levels without symptoms of hyperthyroidism.

A TSH level of less than 0.1 mIU/L combined with high thyroid hormone levels indicates severe hyperthyroidism. People with severe overactive thyroid usually have symptoms of hyperthyroidism.

Treatment Options and Managing Hyperthyroidism

Medications for Hyperthyroidism

Antithyroid medicines, such as methimazole and propylthiouracil, are used to treat hyperthyroidism. They cause the thyroid gland to make less thyroid hormone. Most people need to take these medications for 1-2 years or longer. However, they are not a permanent cure for hyperthyroidism. Learn more: “What Are Some Signs My Thyroid Medication Is Not Working?” 

Thyroid Surgery

Surgical removal of part of most of the thyroid gland (thyroidectomy) is reserved for rare cases. It may be recommended for people with large goiters, suspected thyroid cancer, or pregnant women who cannot take antithyroid medicines. After thyroidectomy surgery, you need to take lifelong thyroid hormone medicine. 

Radioiodine Therapy

Radioiodine therapy is a common and effective treatment for overactive thyroid. It involves taking a capsule or liquid containing radioactive iodine by mouth. This treatment destroys cells in the thyroid gland that make thyroid hormone without affecting other tissues in the body.

However, almost everyone who gets radioactive iodine treatment develops hypothyroidism (underactive thyroid), which needs to be treated with thyroid hormone medicine. 

Beta Blockers

Beta-blocker medicines are used to treat symptoms of hyperthyroidism, such as rapid heartbeat, tremors, and nervousness. They work fast and can provide relief until other treatments like antithyroid medications take effect. 

Learn more about taking beta-blockers for anxiety.

Lifestyle Adjustments and Dietary Considerations

Along with medications for hyperthyroidism, the following lifestyle changes can help in managing the condition:

Diet

Eat a healthy, well-balanced diet with fresh vegetables and fruits, healthy whole grains, and lean proteins. 

People with hyperthyroidism may experience weight loss. If this is the case, talk to your doctor about healthy ways to include more calories in your diet. On the other hand, treatment for hyperthyroidism can lead to weight gain when thyroid hormone levels decrease to normal ranges. In this case, work with your health care provider to develop a healthy eating plan and exercise regimen to maintain a healthy weight.

The thyroid gland uses iodine to make thyroid hormones. Too much iodine in your diet can make hyperthyroidism worse. Your healthcare provider may recommend a low-iodine diet. The low-iodine guide by the American Thyroid Association is a good resource for what foods to eat and what foods, supplements, and medications to avoid while on a low-iodine diet.

Exercise

Get regular exercise to maintain a healthy weight. Check with your doctor before starting any new exercise program. Vigorous or high-intensity exercises may not be safe if you have just been diagnosed with hyperthyroidism and have symptoms such as a fast heart rate. Start with low-intensity exercises such as walking and yoga before moving on to more intense exercise routines.

Dietary Supplements and Natural Remedies for Hyperthyroidism

Evidence-based medicine does not recommend any specific herbal supplements that are proven effective for hyperthyroidism. Keep in mind that dietary supplements do not come under the oversight of the U.S. Food and Drug Administration (FDA). Therefore, taking these natural remedies can be potentially risky. 

However, if your blood tests show deficiencies in certain nutrients, your doctor may recommend dietary supplements. For example, calcium deficiency is frequently noted in hyperthyroidism patients, and your provider may recommend taking supplements.

Importance of Regular Check-Ups and Lab Tests

It is important to keep all your medical and laboratory appointments during hyperthyroidism treatment. Your doctor may order blood tests every few weeks in the beginning to adjust your medication dosage. Typically, less frequent tests (every few months) are required once you have stable thyroid levels.

Living with Hyperthyroidism: Prognosis, Complications, and Quality of Life

Long-term Outlook and Remission Rates

You may need to take antithyroid medication for several years to lessen symptoms of hyperthyroidism. 

Antithyroid drug treatment for hyperthyroidism is associated with a long-term remission rate of approximately 50% (ranges between 30% to 70%). 

The longer the duration of the treatment, the higher the remission rate. For example, in the United States, 12-18 months of treatment with antithyroid medicine is the average, and it is associated with remission rates of 20%-30%. In Europe, treatment for 5-6 years is associated with remission rates of 50%-60%.

Potential Complications: From Heart Issues to Thyroid Eye Disease

Untreated hyperthyroidism can cause serious health problems, including:

• Irregular heartbeat, which can cause blood clots, heart problems, and stroke

• Thyroid eye disease (Graves' ophthalmopathy), with symptoms such as eye pain, light sensitivity, double vision, and rarely, vision loss 

• Osteoporosis (thinning bones)

• Fertility problems in women

• Pregnancy complications, including hypertension, premature birth, low birth weight, and miscarriage (learn about high-risk pregnancies)

• Thyroid storm

Support Groups

• Graves Disease & Thyroid Foundation has resources to help you better understand the symptoms and treatments for Graves' disease (a common cause of hyperthyroidism) and other thyroid-related disorders. 

• Listen to Your Eyes is an informational website for patients with thyroid eye disease. 

• Online support groups offer webinars and sessions and invite medical experts to answer your questions about hyperthyroidism. 

Stress Management

Nervousness, irritability, and anxiety are common hyperthyroidism symptoms and can be aggravated by stress. Stress management techniques such as deep breathing exercises, meditation, yoga, and nature walks can complement hyperthyroid treatment. 

Hyperthyroidism FAQs

What are the 3 types of hyperthyroidism?

The three most common types of hyperthyroidism are Graves’ disease (toxic diffuse goiter), overactive nodules (toxic multinodular goiter), and functional benign thyroid tumor (toxic adenoma).

What is FT3 in hyperthyroidism?

FT3 is free T3 (or free triiodothyronine), a type of thyroid hormone. Notably, free T3 assays are often unreliable. Therefore, it is not routine blood work used to assess thyroid function mL. High levels of free thyroid hormones (T3 and T4) in the blood can be a sign of overactive thyroid or hyperthyroidism. 

What is a bad number for hyperthyroidism?

Normal thyroid stimulating hormone (TSH) levels in adults are 0.5 to 5 mIU/L. TSH levels below 0.4 mIU/L indicate hyperthyroidism.

What level is severe hyperthyroidism?

Thyroid levels (TSH) below 0.1 mIU/L indicate severe hyperthyroidism and may be associated with severe symptoms.

Conclusion: Navigating Your Path With Hyperthyroidism

Summary of Key Points

Hyperthyroidism or overactive thyroid is a condition in which the thyroid gland makes too much thyroid hormone. This can cause a range of uncomfortable symptoms. It can also have a negative effect on many body tissues if left untreated. Causes of hyperthyroidism include autoimmune disorders such as Graves’ disease and thyroid nodules. 

Doctors can make a hyperthyroidism diagnosis based on your history, physical exam, blood tests, and imaging studies. Treatments for hyperthyroidism include antithyroid drugs, medications such as beta blockers to lessen symptoms, radioiodine therapy, and thyroidectomy surgery. Lifestyle adjustments can also help you feel better during hyperthyroidism treatment.

Ongoing Education and Care Management

Hyperthyroidism causes many uncomfortable symptoms and affects multiple organ systems in your body. It is important to follow your doctor’s treatment plan carefully and attend all medical and lab appointments. Learning about your condition can help you understand how to get the maximum benefit from your prescribed hyperthyroidism treatment.