Hyperthyroidism vs Hypothyroidism: What’s the Difference?

With up to 20 million Americans suffering from some form of thyroid illness, hyperthyroidism and hypothyroidism are important public health concerns that affect a significant portion of the population. While both illnesses are related to the rate of hormone production by the thyroid gland, and despite their similar sounding names, these illnesses are distinct and have marked implications on both the short-term and long-term health of those suffering from them. So, what’s the difference between hyperthyroidism vs. hypothyroidism? 

While the former is a condition that stems from excessive production of the thyroid hormones, the latter is a result of deficient thyroid hormone synthesis and secretion. While these conditions seem like opposites when it comes to the rate of hormone secretion, they tend to have overlapping and common symptoms - making the distinction between hypo vs. hyperthyroidism fairly complex.

We discuss the differences between the two conditions, right from their causes, the symptoms, their complications, and potential treatment options for both illnesses to help you better understand these two important endocrine illnesses. 

what is the difference between hypothyroid and hyperthyroid


  • To understand the differences between hyperthyroidism vs. hypothyroidism, it is essential to understand both these diseases in and of themselves. 
  • Hypothyroidism arises when there is an insufficient level of circulating thyroid hormones - T3 or tri-iodothyronine, and T4 or thyroxine
  • Due to the low circulating levels of these important thyroid hormones, the pituitary gland increases the secretion of the TSH (thyroid stimulating hormone) in an attempt to get the thyroid gland to increase the secretion of T3 and T4. This causes an increased level of TSH in individuals suffering from hypothyroidism. 
  • Since thyroid hormones are regulatory hormones that govern your body’s metabolic rate, hypothyroidism will often lead to a slow metabolism. 
  • The low metabolic rate leads to sudden and often drastic weight gain in individuals with hypothyroidism. 
  • Changes to the resting heart rate, including low energy levels, and fatigue are commonly noticed by people suffering from hypothyroidism. 
  • Despite the differences with hyperthyroidism, hypothyroidism might have similar causes such as autoimmune disease and inflammation of the thyroid. 


  • Understanding the traits of hyperthyroidism is integral to decoding the differences between hypothyroid vs. hyperthyroid disease.
  • As opposed to hypothyroidism, the thyroid gland in a person with hyperthyroidism produces an excessive amount of the thyroid hormones - T3 and T4. 
  • Due to the already increased circulating levels of both thyroid hormones, the pituitary gland reduces the secretion of the TSH in an attempt to bring down the levels of the thyroid hormones. Increased levels of T3 and T4 with a reduced TSH level are often indicative of hyperthyroidism.
  • The basal metabolic rate shoots up due to the increased levels of thyroid hormones in the bloodstream. This leads to symptoms such as an increased heart rate, and an initial spurt in energy levels. However, the consistently high rate of metabolic activity causes the body to become fatigued easily and often without activity. 
  • Hot flashes, sudden bursts of sweating, and a fast heartbeat are very common if you suffer from hyperthyroidism. 
  • Like hypothyroidism, its counterpart also is caused by autoimmune illness and inflammation in the gland, among other causes. 

hyperthyroidism vs hypothyroidism

Hyperthyroidism vs. Hypothyroidism: The Causes

  • While both illnesses that affect your thyroid might have similar causes, they also have distinct characteristics and features that set them apart from the other. 
  • Below, we cover the differences between the causes of both hypo vs. hyperthyroidism: 

Hypothyroidism & Its Causes

There exist several causes if you suffer from an underactive thyroid. However, some of the most important causes of the condition include:

  • Congenital anomalies: Children are sometimes born with either a partial or completely missing thyroid gland that can lead to either an impaired production of thyroid hormones or a total lack of them. 
  • Autoimmune illness: An autoimmune condition called Hashimoto’s thyroiditis is among the most common causes of hypothyroidism. The gland is attacked by the body’s immune system, which destroys the thyroid gland’s hormone-producing cells. This autoimmune disease is more likely to affect women and can lead to a complete cessation of thyroid hormone production. 
  • Iodine deficiency: A diet deficient in Iodine can greatly affect thyroid function and completely hamper the synthesis of thyroid hormones. Deficiency of Iodine leads to enlargement and swelling of the thyroid, called goiter. This occurs due to the gland’s attempt at absorbing all the Iodine it can from the bloodstream. 
  • Surgery: For individuals with a history of other autoimmune diseases like Grave’s disease or thyroid cancer, either partial or complete thyroid removal is the suggested mode of treatment. The removal of the gland leads to a total reduction in hormone secretion and can lead to hypothyroidism. 
  • Radiotherapy: Radiotherapy is used as a treatment option for individuals suffering from cancer. However, radiotherapy can sometimes end up damaging the thyroid gland and its cells that produce the important thyroid hormones. 
  • Thyroiditis: This is the inflammation of the thyroid gland that can arise due to an infection by either viruses or bacteria. It can also occur due to conditions such as atrophic thyroiditis. 
  • Pituitary Gland Malfunction: Any damage or illness of the pituitary gland can lead to an abnormal secretion of TSH, which can hamper the overall function of the thyroid gland leading to hypothyroidism. Damage to the pituitary gland leads to either hyper or hypothyroid illness, making it a potentially common cause for both illnesses. 
  • Side Effects from Medications: In people that have certain genetic predispositions and vulnerabilities, medications such as lithium, interferon alpha, interleukin - 2, and amiodarone can result in reduced thyroid function and cause hypothyroidism.
  • Genetic Illnesses: Inherited genetic illnesses such as amyloidosis and hemochromatosis can damage the thyroid gland by deposition of substances in the hormone-producing areas of the gland, leading to impaired function of the gland.

Hyperthyroidism & Its Causes

A hyperactive thyroid gland can be caused by a variety of reasons, many of them similar to those causing an underactive thyroid gland. However, many of them are distinct from the causes of hypothyroidism, allowing you to distinguish between hypo vs. hyperthyroidism. These causes are: 

  • Thyroid Nodules: While thyroid nodules are associated with both hyper and hypothyroidism, nodular goiter can lead to hyperthyroidism. Called toxic multinodular goiter, this can lead to a major increase in thyroid hormone levels. Thyroid nodules can also develop due to inflammatory diseases or even cancer. 
  • Thyroid Cancer: Cancers of the thyroid gland can often lead to a spike in the production of thyroid hormones. This especially occurs when the tissues making the hormones are part of the tumor. 
  • Autoimmune Illness: Autoimmune illnesses like Graves’ disease is the most common cause of hyperthyroidism. Antibodies generated by the immune system constantly trigger thyroid hormone synthesis in the gland, while damaging it simultaneously, leading to a consistently high level of thyroid hormones in the bloodstream. 
  • Thyroiditis: Inflammatory conditions affecting the thyroid gland can cause an increase in the rate of hormone production. While this might be a temporary increase in the levels of the thyroid hormones, it can still have a significant effect on your body. The condition then reverses and becomes a hypothyroid illness after the temporary spike has passed. 
  • Iodine deficiency: While Iodine deficiency can lead to a reduction in thyroid function and the production of thyroid hormones, the normalization of thyroid intake can lead to a sudden yet temporary increase in the levels of thyroid hormones. The levels eventually stabilize, however, the high levels can remain until the gland returns to its normal size and function. 
  • Excessive Artificial Thyroxine Intake: Man-made thyroxine is a medication used to treat hypothyroidism. An excessive amount of the medication can lead to increased levels of the hormone in your body, leading to symptoms of hyperthyroidism. 

Hyper vs. Hypothyroidism: The Symptoms

So what’s the difference between hypothyroid and hyperthyroid illness’ symptoms? Let’s take a look: 

  • Symptoms of Hypothyroidism
    • Fatigue and tiredness due to a slow metabolism
    • Feeling cold despite warm weather due to the body’s inability to metabolize fat effectively and maintain body temperature in the absence of sufficient thyroid hormones
    • Constipation & digestive issues
    • Getting tired by even the mildest forms of exercise
    • Sudden, and often drastic weight gain due to a slow metabolism
    • A reduced appetite
    • Puffy face and water retention 
    • Hair loss
    • Insomnia 
    • Dry, patchy skin
    • Irregular menstrual cycle 
    • Infertility 
    • Miscarriage 
    • Erectile dysfunction 
    • Reduced libido 
  • Symptoms of Hyperthyroidism
    • Fatigue and tiredness due to the constantly high rates of metabolism. 
    • Hot flashes and sensitivity to heat despite cold external temperatures as the body metabolizes fat at a faster rate than normal, leading to increased internal body temperatures
    • Sudden, drastic weight loss due to a rapid metabolism
    • Arrhythmia 
    • Increased heart rates 
    • Diarrhea 
    • Smooth, sometimes textureless skin 
    • Hair Loss 
    • Anxiety 
    • Insomnia 
    • Bulging eyes 
    • Muscle tenderness and fatigue 
    • Soft, flaky nails 
    • Irregular periods

Hyperthyroidism vs. Hypothyroidism: Complications

Both hypothyroid vs. hyperthyroid illnesses can lead to complications arising from these illnesses. Some of the complications arising from them are listed below: 

  • Complications of Hypothyroidism
    • Anemia 
    • High cholesterol levels 
    • Peripheral neuropathy and nerve damage 
    • Muscle wasting 
    • Myxedema 
    • Goiter 
    • Infertility 
  • Complications of Hyperthyroidism
    • Osteoporosis 
    • Atrial fibrillation 
    • Thyroid storm 
    • Goiter 
    • Miscarriage and stillbirth 

hypo vs hyperthyroidism

Hyperthyroidism vs. Hypothyroidism: Treatment Options

  • An important difference between hyper vs. hypothyroidism is that hypothyroidism cannot be cured entirely. However, you can manage the illness with artificial thyroxine (T4) prescribed by your doctor. 
  • Before commencing treatment, your doctor will first get your thyroid levels tested to understand the extent of the illness.
  • In addition to the synthetic T4, your doctor might even prescribe synthetic T3 to help you better manage your hypothyroid illness. 
  • Complications such as myxedema are managed separately using emergency protocols. 
  • Hyperthyroidism, on the other hand, is treatable and has several treatment modalities. 
  • Surgical modalities, treatment with radioactive iodine, and management with antithyroid drugs are often the chosen methods of treatment. 
  • Symptomatic treatment for the symptoms caused by hyperthyroidism is also important to permanently address the condition. 

While both hypo vs. hyperthyroidism have a fairly considerable amount of overlap in symptoms and complications, they’re distinct illnesses that have far-reaching consequences on your body’s day-to-day functioning. Get in touch with your healthcare practitioner if you feel like you suffer from either of these conditions.