Hypothyroidism vs. hyperthyroidism: the key differences explained

Medically reviewed by Rosanna Sutherby, PharmD on April 13, 2020. Written by Jordana White. To give you technically accurate, evidence-based information, content published on the Everlywell blog is reviewed by credentialed professionals with expertise in medical and bioscience fields.

Table of contents

• What is hypothyroidism?
• What is hyperthyroidism?
• Can you have both hyperthyroidism and hypothyroidism?
• Can hypothyroidism be converted to hyperthyroidism?

Changes in thyroid hormone levels can cause hypothyroidism (underactive thyroid) and hyperthyroidism (overactive thyroid). Understanding how these two main forms of thyroid dysfunction are different can help you discuss concerns and questions about your thyroid function with your healthcare provider.

Check if your thyroid hormones are balanced from the convenience of home with the Everlywell at-home Thyroid Test.

Here, you'll discover the common thyroid symptoms that may indicate a thyroid disorder, their main causes, treatment options for each thyroid disease, and more. While both these conditions are related to your thyroid function, they each produce different symptoms in your body (although there are some overlapping symptoms between the two conditions).

Let's start by taking a look at how hypothyroidism vs. hyperthyroidism are different.

What is hypothyroidism?

If you have hypothyroidism, or an underactive thyroid, your thyroid gland fails to produce sufficient hormones to meet your body's needs. Typically, thyroid stimulating hormone levels (or TSH levels) are elevated in hypothyroidism cases, as the pituitary gland attempts to stimulate the thyroid to produce more hormones.

What are the signs and symptoms of hypothyroidism?

With an underactive thyroid, you might not notice any symptoms in its early stages. Over time, however, symptoms of hypothyroidism will appear – and can include:

• Weight gain, even without changes in your diet or activity level
• Fatigue
• Chronic hoarse voice
• Dry skin
• Constipation
• Puffy face
• Joint pain
• Muscle weakness or aches
• Thinning hair or hair loss
• Heavy or irregular periods
• Infertility
• Goiter (enlarged thyroid gland, which usually appears as a lump at the base of your throat)

If you're experiencing symptoms like unexplained weight gain or fatigue, consider scheduling an Everlywell Thyroid Virtual Care Appointment to discuss your concerns and work towards appropriate treatment.

Causes of hypothyroidism

While some babies are born with an underactive or missing thyroid gland (congenital hypothyroidism), you usually develop hypothyroidism later on in life. For adults, the most common cause of hypothyroidism is an autoimmune disease known as Hashimoto's thyroiditis. This condition causes your body's immune system to produce antibodies that attack the thyroid tissue, leading to a gradual decline in thyroid hormone production.

Additionally, some pregnant women develop hypothyroidism after giving birth (known as postpartum thyroiditis), because pregnancy triggers the body to start producing thyroid gland antibodies. Certain medications may also trigger hypothyroidism, and a diet too low in iodine could also trigger an underactive thyroid – so check out what foods can help your thyroid. Understanding the risk factors for hypothyroidism in women is crucial for effective management and prevention.

Treating hypothyroidism

Treating hypothyroidism involves a thorough understanding of the condition, including recognizing the signs of an underactive thyroid. If your thyroid test and a healthcare's evaluation reveals an underactive thyroid, your healthcare provider will likely prescribe a daily dose of synthetic thyroid hormone.

What is hyperthyroidism?

Hyperthyroidism is also referred to as an overactive thyroid gland. With this condition, your thyroid produces too much of the thyroid hormone called thyroxine (T4). The pituitary gland – which is responsible for thyroid stimulating hormone production – responds to excess T4 by producing less of those hormones. This mechanism leads to a reduction of the body’s TSH level, as opposed to the elevated TSH level seen in hypothyroidism.

What are the signs and symptoms of hyperthyroidism?

If your thyroid is overactive, you may experience a wide range of symptoms. Keep in mind, however, that these symptoms of hyperthyroidism can mimic many other conditions, so thyroid testing and talking with your healthcare provider can help you get to the bottom of symptoms you're experiencing. With hyperthyroidism, you may experience:

• Unintentional weight loss, even without dietary changes
• Rapid heartbeat (known as tachycardia)
• Irregular heartbeat (arrhythmia) and a pounding heart (called palpitations
• Increased appetite
• Mood changes, including nervousness, anxiety and irritability
• Hand and finger tremors
• Sweating
• Changes in your menstrual cycle
• New or worsened heat sensitivity
• More frequent bowel movements
• An enlarged thyroid gland (goiter)
• Fatigue
• Muscle weakness
• Problems with your sleep
• Thinner skin, which is more susceptible to cuts and bruises
• Fine hair which easily breaks

Causes of hyperthyroidism

The most common cause of hyperthyroidism is Graves' disease, an autoimmune disorder. When you have Graves' disease, your body releases antibodies which make your thyroid gland produce too much of the thyroid hormone known as T4. Additionally, if you develop thyroiditis – or inflammation of the thyroid gland – your thyroid could become overactive, triggering hyperthyroidism. Hyperthyroidism can also be triggered by thyroid nodules, or lumps in your thyroid gland (known as toxic multinodular goiter).

Treating hyperthyroidism

How you treat an overactive thyroid will likely depend on the severity of your signs and symptoms. Your healthcare provider may prescribe antithyroid medications to block your production of thyroid hormones. If your symptoms are more severe, you may need radioactive iodine therapy, which is designed to damage your thyroid cells in an effort to block hormone production. (This is the most common form of treatment for cases of hyperthyroidism.) Finally, in very rare cases, you may require surgery to remove your thyroid gland, if other treatments prove ineffective.

Can you have both hyperthyroidism and hypothyroidism?

After discovering more about the symptoms of hypothyroidism vs. hyperthyroidism, you may be wondering: can you have both hypothyroidism and hyperthyroidism at the same time?

Thankfully, the short answer to this question is "no." Your body can't simultaneously experience hypothyroidism and hyperthyroidism. Some people, however, do transition between the two conditions, so it's possible to experience both kinds of thyroid problems in your lifetime. In fact, you can experience both conditions in the span of a few years or months.

Sometimes, the shift between hypothyroidism and hyperthyroidism is a direct result of thyroid condition treatment, such as thyroid surgery. Other times, however, this shift occurs spontaneously in your body. However, this type of spontaneous transition from hypothyroidism to hyperthyroidism (or vice versa) is rare.

When switches between under- and over-production of thyroid hormones are related to your thyroid condition treatment, it's important to check with your healthcare provider regarding your medications or other therapies. Simple tweaks to your treatment protocol may be able to restore your hormonal balance.

Can hypothyroidism be converted to hyperthyroidism?

When hypothyroidism is treated with synthetic thyroid hormones, your healthcare provider will carefully monitor your TSH levels for weeks or months following the start of your treatment. This monitoring is necessary because if you take too much thyroid hormone, your body could convert hypothyroidism to hyperthyroidism. If your body has shifted from an underactive thyroid gland towards an overactive thyroid gland, discuss your next-step options with your healthcare provider or our Everlywell Virtual Care Team. In many cases, hormone balance can be restored by simply adjusting thyroid medication levels.

Related content:

What are free T3 and T4 and how can you test for them?

23 possible symptoms of an overactive thyroid

What are the potential early signs of thyroid problems?

Can hypothyroidism cause high blood pressure?

References

1. Hypothyroidism (underactive thyroid). Mayo Clinic. URL. Accessed April 13, 2020.

2. Hyperthyroidism (overactive thyroid). Mayo Clinic. URL. Accessed April 13, 2020.

3. Wong M, Inder WJ. Alternating hyperthyroidism and hypothyroidism in Graves' disease. Clin Case Rep. 2018;6(9):1684–1688. doi:10.1002/ccr3.1700