How Do Doctors Define Hyperthyroidism?

In the US, more than 1 in 100 people over age 12 have an overactive thyroid.¹ An overactive thyroid is also known as hyperthyroidism. This medical condition can cause insomnia, unexplained weight loss, anxiety, and an irregular heartbeat.

There are many treatment options available if you have hyperthyroidism. Dietary changes, medication, and surgery can help restore normal thyroid function and ease (or stop) symptoms. If you've been diagnosed with hyperthyroidism or have a family history of thyroid problems, learning more about this condition could help you identify the early warning and access proper care.

In this article, you'll learn how doctors define hyperthyroidism, the symptoms of this common condition, the many treatment options, and when to see a doctor for screening and advice.

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First, what is the thyroid?

Your thyroid is a gland in your neck that sits between the voice box and collarbone. It's a part of your endocrine system, which includes other hormone-producing parts of the body, such as the pituitary gland and the pancreas.

Your thyroid's job is to produce two essential hormones, triiodothyronine (T3) and thyroxine (T4). These hormones regulate how energy is used and stored (your metabolism). This process also influences your heart rate and breathing.

The pituitary gland (in your brain) controls the thyroid by producing a  thyroid-stimulating hormone (TSH). TSH signals the thyroid to start producing T3 and T4 hormones. The thyroid then sends T3 and T4 hormones into the blood and throughout your body.

What is hyperthyroidism? 

Hyperthyroidism is a medical condition in which your thyroid gland produces too much thyroid hormone. "Hyper" means "excessive," so hyperthyroidism means there is an excessive amount of thyroid hormone in your body.

Hyperthyroidism is also known as having an overactive thyroid — it causes your body's metabolism to speed up.  This condition has many possible symptoms, including

How serious is it?

The severity of hyperthyroidism varies. Some people may experience symptoms so mild they don’t notice them. Others experience symptoms that can become life-threatening.

Fortunately, hyperthyroidism is a very treatable condition. With suitable treatment, most people can manage their symptoms and normalize their thyroid hormone levels.

Why might you have an overactive thyroid?

Knowing why your thyroid produces excessive T3 and T4 hormones helps your doctor create an appropriate treatment plan. To determine the underlying cause, they may use blood tests and imaging scans to determine the underlying cause.

Here are some of the most common hyperthyroidism causes

  • Graves' disease This condition causes your thyroid to grow and produce too many thyroid hormones. Graves disease is the most common cause of hyperthyroidism, accounting for more than 70% of overactive thyroid diagnoses.²

  • Overactive thyroid nodulesSmall nodules (lumps) that form on the thyroid can stimulate it to produce excess hormones.

  • ThyroiditisInflammation of the thyroid gland can cause hyperthyroidism.

  • Too much iodine in your diet

The thyroid requires iodine to produce hormones. Therefore, eating a diet that’s too high in iodine-rich foods may overstimulate the thyroid. (Be sure to continue and read the section ‘Dietary Changes’).

  • Pituitary tumorThe pituitary gland controls thyroid function, so a tumor in this gland could release too much thyroid-stimulating hormone (TSH). 

  • Thyroid medicationIf you are currently taking thyroid medication, taking too much could cause your thyroid to overproduce hormones. Your doctor may adjust your medication to counteract this.

How is hyperthyroidism (overactive thyroid) clinically defined? 

Hyperthyroidism is a condition in which your thyroid produces more triiodothyronine (T3) or more thyroxine (T4) than you need (possibly too much of both).

It's most commonly diagnosed with a blood test to measure thyroid hormone levels and thyroid-stimulating hormone (TSH) levels

What level of TSH equals hyperthyroidism?

Once your doctor examines your blood test results, they will study how many milliunits per liter (mU/l) of TSH are in your blood. The table below indicates TSH ranges that are low, normal, or high.

What's the difference between hyperthyroidism and hypothyroidism?

If you have low levels of thyroid-stimulating hormone (TSH) in your blood, it indicates that you have hyperthyroidism. If you have high levels (between 4 and 10 mU/l) of TSH in your blood, it indicates that you have hypothyroidism

As mentioned earlier, “hyper" means excessive, so hyperthyroidism means you have an excessive amount of thyroid hormones in your body, which can cause symptoms like insomnia, racing heartbeat, weight loss, and muscle tremors.

"Hypo," on the other hand, means "too little" or "less than normal." So, hypothyroidism means you have less than normal amounts of thyroid hormone in your bloodstream. This can cause symptoms such as fatigue, weight gain, dry skin, and constipation.

Hypothyroidism is a common side effect of thyroid removal — a surgical intervention for those with severe hyperthyroidism. Hypothyroidism is commonly managed with daily thyroid hormone supplements to bring thyroid hormones back into the normal range. 

Who is at risk?

Though anyone can develop hyperthyroidism, a few factors could mean you are at greater risk:


If you are female, you are 5 – 8 times more likely to develop hyperthyroidism than males³

Family history

Overactive thyroid is common in families with a history of Graves' disease


Risk of hyperthyroidism is higher if you smoke/used to be a smoker 


You eat a diet rich in iodine (or take medication containing iodine)

Other conditions

If you are diagnosed with Type I diabetes, primary adrenal insufficiency, or pernicious anemia, you have a greater likelihood of developing hyperthyroidism

It’s also worth noting that you may not have any of these risk factors and still develop hyperthyroidism.

If you are experiencing any of the symptoms associated with hyperthyroidism, talk to your doctor about monitoring your thyroid levels, which can be accomplished with a simple blood test.

Your doctor will work with you to find a treatment protocol that works for you, eases your symptoms, and returns your hormones to the normal range. Most people respond well to non-invasive treatment options such as dietary changes and medication.

How is hyperthyroidism diagnosed?

If your blood test indicates hyperthyroidism, your doctor will want to determine the cause. So they may run further blood tests or request an imaging scan using an MRI, CAT scan, or ultrasound. These imaging scans can tell your doctor whether it's your entire thyroid gland that's overactive or if nodules or inflammation are to blame.

You may receive a small dose of radioactive iodine in an oral capsule (a radioactive iodine uptake test). Next, your thyroid function will be evaluated using a handheld device called a gamma probe. The scan doesn’t cause any pain or discomfort, but it takes about 30 minutes.

What are the treatment options for hyperthyroidism? 

Hyperthyroidism is treatable. With the right combination of dietary changes, medication, and other treatments, those with hyperthyroidism can reduce the severity of their symptoms or eliminate them. While the condition often requires a lifetime of treatment, it's very manageable in most cases.

When determining the best combination of treatment options, your healthcare team will take into account factors such as your age, lifestyle, the severity of your symptoms, and whether or not you are pregnant.

Dietary Changes

Changes to your diet could help control your thyroid levels without medication or other treatment options. Your thyroid needs iodine to make both T3 and T4 hormones. It gets this iodine from the food that you eat. So eating too many foods rich in iodine could worsen hyperthyroidism.

By reducing or eliminating these foods from your diet, your thyroid may not get as much iodine and reduce the amount of thyroid hormone it makes.

High in iodine foods include

  • Kelp

  • Seaweed

  • Fish

  • Shrimp

  • Milk

  • Yogurt

  • Cheese

  • Iodized salt

You may also be taking medication or supplements that have iodine in them (such as iodine caplets or kelp supplements).

When discussing your treatment options, talk to your doctor about your diet, medication, and any supplements you take.

Radioiodine Therapy

Radioiodine therapy involves administering a small amount of radioactive iodine (orally), which destroys some of the cells in the thyroid gland without impacting other areas of the body. Over several months, this will reduce the amount of T3 and T4 hormones that your thyroid can produce. You may need more than one course of radioiodine treatment to bring your thyroid hormone levels back into the normal range.

For some people, radioiodine treatment leads to the thyroid being unable to make enough of the necessary hormones later on. In these cases, thyroid medication will be given to bring your hormone levels up and keep them within the normal range for the rest of your life. This form of therapy is a permanent, long-term treatment option for hyperthyroidism that doesn't require surgery. However, it is not suitable if you are pregnant, plan on becoming pregnant, or are currently breastfeeding.


There are several medication options for the treatment of hyperthyroidism. A doctor may recommend one or a combination of the following:

Anti-thyroid drugs

Commonly prescribed anti-thyroid medications include methimazole and propylthiouracil. These drugs work by preventing the process required for the thyroid to create T3 and T4 hormones. They will gradually reduce the hormone levels in the blood over several weeks.

A doctor may prescribe anti-thyroid drugs for short-term use (such as before radioiodine treatment). They may also prescribe them for long-term use for anyone who wants to avoid more invasive treatment options. 

Some anti-thyroid medications aren't suitable during pregnancy or if you plan to conceive in the future.


Common beta-blockers for the treatment of hyperthyroidism include atenolol and propranolol. You can usually start beta-blockers as soon as you are diagnosed with hyperthyroidism.

Beta-blockers work by blocking the effects of certain hormones within the body.

These drugs can help prevent symptoms associated with hyperthyroidism, such as a rapid heart rate, insomnia, and muscle tremors.

Most people can stop taking beta-blockers once their thyroid levels are within a normal range. Still, be sure to check with your doctor before making medication changes.


While many people with hyperthyroidism respond well to non-invasive treatments, surgical treatment options are also available. Surgery for hyperthyroidism involves removing all or part of the thyroid gland.

Surgery might be the best option if

  • Your thyroid gland is very swollen

  • Thyroid problems are causing other medical issues, such as eye problems

  • Other therapies haven’t been successful

  • You are pregnant

Following thyroid surgery, many people develop hypothyroidism. If you develop hypothyroidism after surgery, you will need to stay on thyroid replacement medication to bring your hormone levels back into the normal range.

While there is a risk of complications with any surgery, thyroid gland removal is considered a low-risk surgery for most people. You should be able to return to your normal activities within a few days. 

How is hyperthyroidism be treated if you are pregnant?

Some treatment options are unsuitable if you are pregnant due to related risks.

However, some hyperthyroid conditions, such as Graves' disease, could pose a risk to the health of the mother and baby if left untreated. Therefore, getting treatment for hyperthyroidism during pregnancy is vital. Graves' disease occurs in between 1 and 4 of every 1,000 pregnancies⁴ in the US.

If you had hyperthyroidism before your pregnancy If you already have an overactive thyroid, your doctor will closely monitor your hormone levels by frequent blood testing. Some mild cases of hyperthyroidism may not require treatment during pregnancy.

In severe cases, your doctor may prescribe propylthiouracil for your first trimester, then switch you to methimazole later.

While methimazole has fewer side effects and is better tolerated, it has been linked with congenital disorders when taken in the early stages of pregnancy.

A study⁵ of 6,000 medical records belonging to pregnant women between 1999-2010 found that “women who took methimazole during the first trimester had double the risk of congenital disabilities, compared to women who took PTU or neither medication.”

Radioiodine treatment is not an option if you are pregnant or hoping to become pregnant soon. Surgery may be the best option in severe cases where medication isn't working.

When to speak to a healthcare professional 

If you are experiencing any of the symptoms associated with hyperthyroidism, make an appointment with your healthcare provider. In some cases, they may refer you to an endocrinologist — an endocrine system specialist.

If you do have hyperthyroidism, in most cases, you can begin exploring treatment options immediately. Your doctor may request additional tests to determine the underlying cause of hyperthyroidism, such as Graves' disease or nodules on your thyroid gland. That can help them tailor your treatment plan and bring your hormone levels back into a normal range.

The lowdown

The thyroid is a butterfly-shaped gland in your neck. It's responsible for creating triiodothyronine (T3) and thyroxine (T4) hormones. These hormones help your body store and use energy. However, too many hormones can cause hyperthyroidism. Common symptoms of hyperthyroidism include insomnia, muscle tremors, unexplained weight loss, increased appetite, and irritability.

Diagnosis begins with a blood test to measure thyroid hormones in your blood along with thyroid-stimulating hormones produced by the pituitary gland in the brain. If you have hyperthyroidism, your doctor might request further tests to determine the underlying cause, most commonly Graves' disease or nodules on the thyroid gland.

Hyperthyroidism is a treatable condition. Treatment options include dietary changes, medication, and surgery. If you are experiencing any of the symptoms of hyperthyroidism, schedule an appointment with a qualified healthcare professional.

  1. Hyperthyroidism (Overactive thyroid) | (NIDDK) National Institute of Diabetes and Digestive and Kidney Diseases

  2. Hyperthyroidism (Overactive) | American Thyroid Association

  3. General information/Pressroom | American Thyroid Association

  4. Thyroid disease & pregnancy | (NIDDK) National Institute of Diabetes and Digestive and Kidney Diseases

  5. Thyroid and pregnancy | American Thyroid Association

General Sources

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