Hypothyroidism vs. Hyperthyroidism: What’s the Difference?

By Edo Paz, MD
Medically reviewed checkmarkMedically reviewed
September 16, 2019

More than 12% of people in the US will develop a thyroid disorder during their lifetime, according to the American Thyroid Association.

Though relatively common, up to 60% of those with a thyroid disorder are unaware of it.

To learn more about thyroid disease and its associated symptoms, it helps to better understand the thyroid itself and the two main types of thyroid disorders: hypothyroidism and hyperthyroidism.

Here, we’ll take a closer look at each of these disorders separately, including their symptoms, causes and treatments.​

What Is the Thyroid?

The thyroid is a butterfly-shaped gland that’s located in the front of our throat.

More precisely, it sits in the middle of our lower neck below our Adam’s apple.

While the thyroid is a small gland, it has a big job: As part of our endocrine system, it produces hormones – triiodothyronine (T3) and thyroxine (T4) – that regulate our metabolism and other bodily functions that are vital for our development.

These functions include:

• Heart rate

• Breathing

• Central and peripheral nervous systems

• Body weight

• Muscle strength

• Menstrual cycles

• Body temperature

• Cholesterol levels

These important T3 and T4 hormones are made from iodine that our thyroid gland takes and converts from food.

They travel throughout our entire bloodstream, regulating the way our cells and metabolism work.

Sometimes, the thyroid gland doesn’t produce enough T3 and T4 hormones, or it produces too much of them.

When levels of these thyroid hormones are too low, the result is an underactive thyroid, called hypothyroidism.

Conversely, if thyroid hormone levels are too high, the result is an overactive thyroid, known as hyperthyroidism.

Given that these thyroid hormones have an enormous influence on every cell, tissue and organ in our body, it’s not surprising that imbalanced levels can create health problems for us.

For example, an underactive thyroid (hypothyroidism) may cause our heart rate to be slower than normal, or may cause us to experience constipation or weight gain.

Conversely, an overactive thyroid (hyperthyroidism) can cause a rapid heart rate, palpitations, diarrhea, or weight loss.

Below, we will discuss the causes, symptoms and treatments of hypothyroidism. We will then separately address hyperthyroidism.

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What Is Hypothyroidism?

As we mentioned, hypothyroidism is an underactive thyroid.

It is a condition in which your thyroid gland doesn’t produce enough T3 and T4 hormones.

As this hormonal imbalance creates a chemical imbalance within your body, it can upset how your tissues and organs function and work.

What is Hyperthyroidism?

Hyperthyroidism occurs as the result of an overactive thyroid.

It’s a condition in which your thyroid gland produces too much of the T3 and T4 hormones.

As this hormonal imbalance creates a chemical imbalance within your body, it can accelerate your body’s metabolism, causing irregular or rapid heartbeats, or unintentional weight loss, among other health issues.


Below we’ll outline the causes of both hypothyroidism and hyperthyroidism.


Hypothyroidism may result from different causes, which can include:

  • Autoimmune disease: The most common cause of hypothyroidism in the US, affecting 5 out of 100 people, is an autoimmune disorder called Hashimoto’s disease or Hashimoto’s thyroiditis. It occurs when your immune system produces antibodies that attack your thyroid gland and affect its ability to produce hormones. The medical community is unsure why this happens, though genetics and environmental triggers could play a part.
  • Hyperthyroidism treatments: When people suffer from hyperthyroidism, or an overactive thyroid gland that produces too much T3 or T4 hormone, they are usually treated with antithyroid medication or radioactive iodine. However, sometimes, when trying to lower the thyroid gland’s hormone production, it gets lowered too much. This can result in permanent hypothyroidism.
  • Radiation therapy: Any radiation used in head or neck cancers can negatively affect your thyroid gland’s ability to function, possibly resulting in hypothyroidism.
  • Thyroid surgery: Taking out a large part or all of your thyroid gland can lower hormone production or stop it altogether. In this case, patients are required to take supplementary thyroid hormones for life.
  • Medication: Certain medications, including Lithium, can contribute to hypothyroidism. If you take any medication, you may want to ask your doctor if it can impact your thyroid function, particularly if you take medication for bipolar disorder, abnormal heart rhythm, or medications that contain iodine

Other, less common causes of hypothyroidism include:

  • Congenital disease: Some babies are born without a thyroid gland or with a defective one. In other cases, children may have inherited a form of hypothyroidism.
  • Pituitary disorder: This occurs when the pituitary gland doesn’t produce enough of the hormone that stimulates the thyroid-stimulating. This is a relatively rare disorder and is usually a result of a benign tumor in the pituitary gland.
  • Iodine deficiency: The thyroid gland needs iodine for hormone production, so any iodine deficiency can lead to hypothyroidism.


Hyperthyroidism may result from a number of different causes, which include:

  • Autoimmune disorder: The most common cause of hyperthyroidism in the US is Grave’s disease, affecting 1 in 200 people. With this autoimmune disorder, the body’s immune system produces an antibody that causes the thyroid gland to produce more thyroid hormone than the body needs. When this overabundance of hormone occurs, it can cause problems with your eyes, skin, heart, muscles, bones, menstrual cycle, and fertility.
  • Thyroid nodules: As the name suggests, a thyroid nodule is when a growth, or nodule, forms on your thyroid gland. Also called thyroid adenoma, around half the US adult population has one or more thyroid nodules, with 90-95% of these nodules being non-cancerous (benign). Thyroid nodules are usually painless and go unrecognized until they become visible on an exam. If they reach a large size, they may cause difficulty swallowing, breathing or lead to hoarseness. In some cases, these nodules may cause hyperthyroidism.


An underactive or overactive thyroid result in different symptoms, take a look at a few below.


The following are typical symptoms of hypothyroidism:

Hypothyroidism symptoms vary, depending on the severity of the body’s thyroid hormone deficiency.

In its early stages, there may not be any noticeable symptoms, which is why people may not know they have hypothyroidism until it has developed into an advanced stage.

As any of these symptoms may develop slowly, even over a number of years, it can be easy to mistakenly attribute them to aging or stress.

However, as your body’s metabolism continues to slow due to this disorder, you can develop more obvious problems.

And, over time, if left untreated, hypothyroidism can cause severe health problems including joint pain, infertility, and heart disease.


Hyperthyroidism can cause a wide range of symptoms, including:

If you have hyperthyroidism, you may be at risk for Graves’ Ophthalmopathy, especially if you smoke.

This is an uncommon condition that causes your eyes to bulge due to swelling of the tissues and muscles behind them.

The good news is that such eye problems typically improve with treatment.

Signs and symptoms of Graves’ Ophthalmopathy include:

  • Red, swollen, dry or protruding eyes
  • Excessive tearing or discomfort in one or both eyes
  • Light sensitivity
  • Blurry or double vision, inflammation, or reduced eye movement

Hyperthyroidism symptoms can be easily mistaken for other health problems, which can make it difficult for you to recognize and your doctor to diagnose.

This is especially the case for older adults, who are more likely to exhibit no symptoms or only subtle ones.

These include intolerance to heat, increased heart rate, and a tendency to tire during regular activities.


It’s important to understand the different ways in which hypothyroidism and hyperthyroidism are diagnosed.


Hypothyroidism is usually diagnosed through thyroid function blood tests.

A physical exam is performed, followed by blood tests, which check levels of thyroid hormone and thyroid stimulating hormone.

Imaging exams like a thyroid ultrasound or a biopsy may also be done.


The first step toward diagnosing hyperthyroidism is a physical exam.

Physical signs can include an enlarged thyroid gland, commonly referred to as goiter, which may appear as a swelling at the base of your neck.

Other obvious signs are hand tremors or irregular heartbeat.

To confirm a diagnosis, your doctor will use a blood test to check levels of your thyroid hormones and thyroid stimulating hormones.

Imaging exams like a thyroid ultrasound or biopsy may also be conducted.

Below we outline related and conditions and risk factors that may relate to hypothyroidism and hyperthyroidism.


One of the most important risk factors for hypothyroidism is female sex.

In fact, Hashimoto’s disease is 8 times more common in women than in men.

While scientists don’t know exactly why, the suspected answer is that Hashimoto’s disease is an autoimmune disease, and autoimmune diseases are generally more common in women than men.

Some women can also develop hypothyroidism during or after pregnancy (postpartum hypothyroidism).

Similar to Hashimoto’s disease, pregnant women can produce antibodies to their own thyroid gland.

If left untreated during pregnancy, hypothyroidism can increase the risk of miscarriage, premature delivery and preeclampsia as well as affect the fetus.

Other risk factors for hypothyroidism include:

  • Age > 60
  • Family history of thyroid diseases
  • Past thyroid problems
  • Prior surgery or radiotherapy affecting the thyroid gland
  • Autoimmune conditions like type 1 diabetes


As with hypothyroidism, women are at an increased risk of developing hyperthyroidism.

Other risk factors include a family history of thyroid diseases. and autoimmune conditions like type 1 diabetes.

Treatment Options

Hyperthyroidism has several treatment options, while synthetic hormones are effective in treating hypothyroidism.


Today, the most effective treatments for hypothyroidism are synthetic thyroid hormones.

These are usually simple, safe and effective.

You may have to be a bit patient, however, since the process of thyroid hormone replacement therapy can take some time until your doctor finds just the right dosage required to bring your thyroid function to a healthy level.


There are several treatments available for hyperthyroidism.

Doctors typically use anti-thyroid medications or radioactive iodine to slow down your body’s production of thyroid hormones.

Depending on the person, it may take weeks or months for the medicine to take effect and the hormone levels to adjust to the normal range.

On average, such treatments tend to last 1-2 years.

Some cases of hyperthyroidism are treated by surgery, where a doctor removes all or part of the patient’s thyroid gland.

When to See a Doctor

If you’re feeling fatigued for no reason, or have any of the other hypothyroidism symptoms listed above, it’s recommended to see your doctor.

Again, some of the signs can easily be mistaken for aging or stress, so it’s better to see a doctor to rule out hypothyroidism than to leave it untreated.

There’s no way to prevent hypothyroidism.

Once you are diagnosed, treatments are effective.

While there are alternative medicines that can help treat thyroid disease, it’s recommended to seek treatment through a doctor.

This is because it’s easier to regulate your hormone levels and gauge how your body is responding to the thyroid replacement treatment with the help of a licensed medical doctor.

It’s also very important to schedule follow-up visits as often as your doctor recommends to ensure that your hormone levels are normal and your thyroid is continuing to function as it should.

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How K Health Can Help

When it comes to thyroid disorders, a clinical diagnosis will result in figuring out the best medical treatment for you. While hypothyroidism and hyperthyroidism can severely affect your body’s overall function, a timely diagnosis can lead to successful treatment. The most important thing to remember when suffering from symptoms of thyroid disorder is to seek medical attention as close to their onset as possible to prevent sustained discomfort and long-term health problems.

K Health’s virtual diagnosis tool can help you very quickly determine whether your symptoms point to hypothyroidism or hyperthyroidism, which will help your doctor pinpoint the most effective medical treatment for you. Treat your thyroid condition online.

K Health articles are all written and reviewed by MDs, PhDs, NPs, or PharmDs and are for informational purposes only. This information does not constitute and should not be relied on for professional medical advice. Always talk to your doctor about the risks and benefits of any treatment.

Edo Paz, MD

Edo Paz is the VP of Medical at K Health. Dr. Paz has two degrees in chemistry from Harvard and earned his medical degree from Columbia University. He did his medical training in internal medicine and cardiology at New York-Presbyterian. In addition to his work at K Health, Dr. Paz is a cardiologist at White Plains Hospital, part of the Montefiore Health System.