Hyperthyroidism occurs when your thyroid gland is overproducing thyroid hormones. This can cause symptoms that may include weight loss and increased appetite.

Several health conditions can lead to hyperthyroidism, most commonly Graves’ disease.

The thyroid is a small, butterfly-shaped gland located at the front of your neck. It produces thyroxine (T4) and triiodothyronine (T3), which are two primary hormones that control how your cells use energy. Your thyroid gland regulates your metabolism through the release of these hormones.

When your thyroid makes too much T3, T4, or both, it speeds up your body’s systems, causing distress. Timely diagnosis and treatment of hyperthyroidism can relieve symptoms and prevent complications.

A variety of conditions can cause hyperthyroidism. Graves’ disease, an autoimmune disorder, is the most common cause of hyperthyroidism. In Graves’ disease, your immune system attacks your thyroid gland with antibodies, resulting in the release of too much hormone.

Graves’ disease occurs more often in women than in men. A 2011 research overview explains that genetics largely determine whether someone will develop Graves’, although environmental factors also play a role. Studies of families and twins indicate Graves’ disease isn’t caused by a single gene defect, but rather by small changes in multiple genes.

Tell your doctor if any relatives have been diagnosed with hyperthyroidism, so they can get an accurate picture of your risk factors.

Aside from Graves’ disease, other causes of hyperthyroidism include:

  • Excess iodine. This mineral is a key ingredient in T4 and T3, and too much iodine can cause temporary hyperthyroidism. Iodine can be ingested through food like fish and dairy. It is also present in certain medications, such as amiodarone (for heart arrhythmia), cough syrups, and medical contrast dyes.
  • Thyroiditis (inflammation of the thyroid). Thyroiditis refers to conditions which cause the thyroid gland to swell, making either too much or too little of the hormone.
  • Benign thyroid nodules. Nodules are lumps that develop on the thyroid gland, often for unknown reasons. Some thyroid nodules produce excess thyroid hormones, but the majority are benign. Nodules are also called benign tumors or adenoma.
  • Toxic thyroid nodules (toxic adenoma). Some thyroid nodules are malignant, or cancerous. Whether a nodule is benign or malignant is determined by ultrasound, or with a kind of tissue biopsy called fine needle aspiration.
  • Tumors of the ovaries or testes.
  • Large amounts of T4 in the blood. High levels of T4 can result from taking certain dietary supplements, or too much of the thyroid hormone medication, levothyroxine.

Thyrotoxicosis and hyperthyroidism don’t mean the same thing, even though they’re sometimes used interchangeably. Hyperthyroidism (and its many forms) are actually all under the umbrella of thyrotoxicosis.

Hyperthyroidism refers to your thyroid’s physical overproduction of hormones. Thyrotoxicosis refers more broadly to the presence of too much thyroid hormone in your body, regardless of whether it came from the gland, medication, or other cause.

Some symptoms of hyperthyroidism may be physically obvious, while others are subtle, and may be hard to notice at first. Sometimes hyperthyroidism is mistaken for anxiety.

According to the National Institutes of Health (NIH), hallmark signs and symptoms of hyperthyroidism include:

  • weight loss, but with an increased appetite
  • rapid or irregular heartbeat
  • feeling nervous or irritable
  • feeling fatigued, but having trouble sleeping
  • hand tremors, muscle weakness
  • getting easily overheated
  • frequent bowel movements

The thyroid gland itself can swell into a goiter, which can be either symmetrical or one-sided. A goiter is an enlargement of the gland, and it’s often visible as a bulge or puffiness at the base of your neck. The most common cause of a goiter is iodine deficiency.

You may also experience prominent or bulging eyes. This is medically known as exophthalmos, and it’s associated with Graves’ disease.

Longterm and untreated thyroid disease can also cause brittle hair, and hair loss.

Irregular heartbeat, trouble breathing, or loss of consciousness can occur in some people with hyperthyroidism. These symptoms require immediate medical attention.

Untreated, hyperthyroidism can contribute to an increased risk of:

  • Thyroid storm. A thyroid storm is a rare health condition that occurs as a result of untreated hyperthyroidism. Your body enters overdrive as a result of too many thyroid hormones in its system. A thyroid storm is a potentially life threatening combination of symptoms including rapid heart rate, high blood pressure, and fever.
  • Pregnancy complications. This includes people with existing thyroid disorders and people who develop hyperthyroidism during pregnancy. High thyroid hormone levels can harm both pregnant people and the fetus. Risks include miscarriage and premature birth. Regular thyroid hormone tests during pregnancy can detect irregularities, and your doctor may determine medication is a good idea.
  • Osteoporosis. Hyperthyroidism can cause your bones to become weak and thin, which can lead to osteoporosis. Taking vitamin D and calcium supplements during and after treatment can help improve bone health. Getting adequate exercise or daily physical activity also helps prevent osteoporosis.
  • Cancer. Some people with hyperthyroidism develop thyroid cancer, called thyroid carcinoma. A 2018 research overview reported that thyroid cancer in hyperthyroid patients was more “aggressive” and had a worse prognosis than in euthyroid patients (those with a healthy thyroid).

Hyperthyroidism can also cause atrial fibrillation, a dangerous arrhythmia (irregular heartbeat) that can lead to stroke, as well as congestive heart failure.

Read more >> The effects of atrial fibrillation on the body

Untreated thyroid disorders take a heavy toll on your body, and can develop into medical emergencies if not treated. Many blood tests used to diagnose hyperthyroidism and other thyroid conditions are straightforward. Talk to your doctor as soon as possible if you think you may be experiencing symptoms of hyperthyroidism.

In evaluating you for hyperthyroidism, a doctor will collect your personal and family medical history, and conduct a physical exam. Doctors usually diagnose hyperthyroidism based on symptoms, clinical signs, and lab tests.

These diagnostic tests include:

  • T4, free T4, and T3 level test. These tests measure how much thyroid hormone (T4 and T3) is in your blood.
  • Thyroid-stimulating hormone (TSH) level test. TSH is a pituitary gland hormone that stimulates the thyroid gland to produce hormones. When thyroid hormone levels are high, your pituitary gland responds by decreasing TSH production. An abnormally low TSH can be an early sign of hyperthyroidism.
  • Thyroid scan (Radioactive iodine uptake scan). This helps your doctor see if your thyroid is overactive by measuring how much iodine it “takes up” from your bloodstream. Your doctor will give you a small tablet or liquid amount of iodine. Then you’ll lie on a table while a special camera takes images of your thyroid. In particular, a thyroid scan can reveal whether the entire gland or just a single area is causing the problem.
  • Ultrasound of thyroid. Ultrasounds can measure the size of the entire thyroid gland, as well as any masses on or in it (such as nodules). Doctors can also use ultrasounds to determine if a mass is solid or cystic.
  • CT or MRI scans. A CT scan or MRI can show if a pituitary tumor is present.

While primary care doctors can order some of these tests, it’s best to see an endocrinologist. Endocrinologists specialize in treating and managing hormone-related health conditions.


Anti-thyroid medications prevent the thyroid from making hormones. The most common anti-thyroid medications are a class called thionamides, which includes the drugs methimazole (MMI) and propylthiouracil (PTU).

Thionamides have been used to treat hyperthyroidism for decades, and are considered safe for both children and adults, including pregnant people. Anti-thyroid medications can have uncomfortable side effects such as joint pain, hair loss, and rash. In rare cases, they can cause liver damage.

Make sure to tell your doctor if you’re pregnant or plan on becoming so, and if you take other medications. Always take medication as directed by your doctor.

Radioactive iodine

Radioactive iodine (RAI), also just called radioiodine, effectively destroys the cells that produce thyroid hormones without damaging other bodily tissues. It is usually taken as an oral tablet or liquid.

Most people who receive radioiodine treatment for hyperthyroidism develop the opposite condition, hypothyroidism. However, this is easier to treat, and you’ll take a daily thyroid hormone supplement. RAI is also used in higher doses to treat thyroid cancer.

In rare cases, at sustained higher doses, RAI is associated with increased risk of certain cancers. This has not been found to be true in lower doses used to treat hyperthyroidism.

Side effects can occur with RAI treatment, especially at higher doses. These include neck pain, nausea, and dry mouth. RAI treatment at high doses can also impact fertility.


During a thyroidectomy, all or part of your thyroid gland is removed. This surgery may be recommended for certain people with hyperthyroidism, but it’s evaluated on an individual basis. Surgery may be used for patients that don’t respond to other treatment options, or can’t partake in them.

Thyroid gland removal is also used to treat types of thyroiditis, thyrotoxicosis, and thyroid cancer.

If your thyroid gland is fully removed, you will need to take thyroid hormone supplements for the rest of your life. The drug levothyroxine (brand names Levoxyl, Synthroid, and others) is a synthetic version of the thyroid’s T4 hormone, and is usually prescribed in pill form. Taking this drug prevents hypothyroidism, an under-active thyroid that secretes too little hormone.

As with all surgeries, thyroid removal comes with risks and complications. The surgery is usually done by an endocrine surgeon, otolaryngologist, or general surgeon.

FDA recall alert

Certain brands and strengths of medication for hypothyroidism (underactive thyroid) have been recalled. This is due to the medication having a less active drug (levothyroxine) than they are supposed to.

You can search all FDA recalls and safety alerts here.

Taking recalled tablets can lead to symptoms of hypothyroidism, such as fatigue, constipation, hair loss, and depression. Reduced effectiveness can be particularly dangerous for older people and those who are pregnant.

Call your pharmacist to find out if your medication has been recalled. Don’t stop taking the medication unless advised to do so by your healthcare professional.

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To summarize, the main risk factors for hyperthyroidism are:

  • Sex. Females are much more likely to have hyperthyroidism than males. Experts believe this may have to do with hormones.
  • Pregnancy. Pregnancy can stimulate hyperthyroidism in some people, which can cause complications for both parent and fetus.
  • Age. You’re considered at higher risk for hyperthyroidism as an older adult, especially after age 60.
  • Genetics. A family history of hyperthyroidism usually indicates an increased likelihood of developing the condition.
  • Iodine exposure. You may get too much iodine from certain medications or foods.
  • Having another health condition. People with type 1 diabetes, primary adrenal insufficiency, or pernicious anemia are considered more at risk.

Lifestyle is an important part of lowering your risk factors for hyperthyroidism. This includes eating a balanced diet, taking nutritional supplements if necessary, and getting adequate physical activity during the week. Work with your doctor to create a plan with individualized goals.

Avoid — or seek to quit — smoking, as this has been found to increase your likelihood of Graves’ disease in particular. A large-scale 2007 study from Norway found smokers had higher levels of thyroid hormone than nonsmokers. The prevalence of hyperthyroidism in women who currently smoked was around twice as high as women who reported never smoking.

There are many reasons your thyroid might start overproducing thyroid hormones.

A genetic predisposition to thyroid conditions like Graves’ disease, having too much iodine in your system, or being pregnant can all contribute to hyperthyroidism. Eating well, exercising, and avoiding smoking can all help reduce your risk.

Hyperthyroidism is diagnosed based on symptoms, blood tests, and imaging. It is treated primarily with medication, radioiodine therapy, and if necessary, surgery to remove all or part of the thyroid gland.

The long-term outlook for hyperthyroidism depends on its cause. Most cases, including Graves’ disease, will worsen without treatment, and can become life threatening. The good news is hyperthyroidism is very treatable, and many people with it are able to get back to full health.

Talk to your doctor if you believe you’re experiencing thyroid-related health concerns. Common symptoms of hyperthyroidism include unplanned weight loss, severe fatigue, and goiter. You may be referred to an endocrinologist, who will evaluate you, and conduct the necessary tests.