Hypothyroidism vs. Hyperthyroidism: What is the difference?

Hypothyroidism vs. Hyperthyroidism: What is the difference?

Hypothyroidism vs. Hyperthyroidism
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As the saying goes, “We don’t appreciate what we have until it’s gone.” This certainly holds true for the thyroid gland, the small, butterfly-shaped gland nestled in your neck. Even though it’s such a vital organ, we barely notice it or even think about it. That is, of course, when it’s functioning properly.

It’s therefore no surprise that thyroid dysfunction is what usually makes it clear how important this organ is. This is mainly because a dysfunctional thyroid causes a range of symptoms that can significantly impact your everyday life.

The state of the thyroid, in terms of function, can be broadly categorized under hypothyroidism (underactive thyroid), hyperthyroidism (overactive thyroid), and euthyroidism (normal functioning thyroid). The first two are two main types of thyroid dysfunction that are opposite each other. To know which thyroid condition you have, a thyroid function test (sometimes in combination with other tests) is necessary. A thyroid function test is a combination of blood tests that measure levels of thyroid-stimulating hormone (TSH) and the thyroid hormones in your blood in order to make a diagnosis or monitor your response to treatment. 

In this article, we will discuss these two thyroid conditions, and also compare them to euthyroidism.

Hypothyroidism (Underactive Thyroid)

What is hypothyroidism and what are the causes?

Hypothyroidism, often referred to as an underactive thyroid, occurs when the thyroid gland does not produce enough thyroid hormones. These hormones, thyroxine (T4) and triiodothyronine (T3), are vital for regulating the body’s metabolic rate. In iodine-sufficient geographical regions, the most common cause is Hashimoto’s thyroiditis, an autoimmune disease. From a global perspective, however, the most common cause is iodine deficiency. Other possible causes of this condition include radiation treatment or exposure and certain medications.

How common is hypothyroidism?

Hypothyroidism is one of the most common endocrine disorders worldwide. Its prevalence varies by age, sex, and geographical location, largely due to differences in iodine intake. It is estimated that hypothyroidism affects about 5% of people above the age of 12 in the United States, while subclinical hypothyroidism, a milder form of the disease, affects at least an additional 5%. Women are more likely to develop hypothyroidism than men, and the risk increases with age.

What are the symptoms?

Symptoms of hypothyroidism develop slowly and can be vague. They include fatigue, weight gain, cold intolerance, constipation, dry skin, hair loss, slow heart rate, muscle weakness, irregular periods, and depression. Because these symptoms can be attributed to other conditions, hypothyroidism can sometimes be overlooked.

How is hypothyroidism treated?

Treatment for hypothyroidism involves a lifelong daily dose of synthetic thyroid hormone levothyroxine. This oral medication restores adequate hormone levels, and as a result reverses the signs and symptoms of hypothyroidism. Taking this medication comes with guidelines that ensure that you get the best possible treatment outcomes. While a majority of patients take levothyroxine, there are some who are prescribed some alternative medication such as the T3+T4 combination therapy. 

In any case, periodic blood tests are performed to assess the effectiveness of the treatment. Based on your lab results, your doctor may decide to adjust your dosage, if necessary. 

Hyperthyroidism (Overactive Thyroid)

What is hyperthyroidism and what are the causes?

Hyperthyroidism occurs when the thyroid gland produces too much thyroid hormone. This overactivity can accelerate the body’s metabolism, leading to rapid weight loss and a bunch of other symptoms. The most common cause of hyperthyroidism is the autoimmune disorder known as Graves’ disease. Other causes include thyroid nodules, and excessive iodine intake.

How common is hyperthyroidism?

Hyperthyroidism is less common than hypothyroidism. It affects about 1% of Americans, with a higher prevalence in women than in men. Graves’ disease in particular is responsible for about 60-80% of cases of hyperthyroidism. Hyperthyroidism can occur at any age but is most commonly diagnosed in people between the ages of 20 and 50.

What are the symptoms? 

The symptoms of this condition include unexpected weight loss, anxiety, irritability, fast heart rate, hand tremors, frequent bowel movements or diarrhea, heat intolerance, and having trouble sleeping. Some people with hyperthyroidism may also experience swelling in the neck due to an enlarged thyroid gland (goiter) or an eye condition known as thyroid eye disease (TED).

How is hyperthyroidism treated?

The treatment of hyperthyroidism aims to reduce thyroid hormone production and may involve radioactive iodine therapy, anti-thyroid medications, or surgery. Your doctor may also prescribe beta-blockers, such as propranolol or nadolol. The purpose of these drugs is to control some of the uncomfortable symptoms associated with high thyroid levels, such as rapid heart rate and anxiety.

Key takeaways

  • Despite their similar names, hypothyroidism and hyperthyroidism have different causes, symptoms, and treatments. 
  • Hypothyroidism is characterized by an underactive thyroid and as a result, low thyroid hormone levels. Hyperthyroidism, on the contrary, is characterized by an overactive thyroid and therefore, high levels of  thyroid hormones.
  • Both conditions can cause fatigue and changes in weight, but the direction of the change is a key difference. Hypothyroidism often leads to weight gain and feeling cold, while hyperthyroidism can cause weight loss and heat intolerance.
  • If you’re experiencing symptoms that might be related to your thyroid, seek immediate medical attention. An early diagnosis and effective treatment can help you manage your condition and get back to feeling your best.
  • Hypothyroidism is usually treated with synthetic thyroid hormone medication, while hyperthyroidism treatment may involve medication, radioactive iodine treatment, or surgery to reduce hormone production.
  • If you’ve been diagnosed with either condition, be sure to follow your treatment plan closely and report any new symptoms to your doctor.


At ThyForLife, we do our utmost to provide accurate information. For detailed medical information regarding diagnosis, treatment, and general practices please consult your healthcare professional. Always listen to the advice of your healthcare provider.
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