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 are the signs and symptoms of hyperthyroidism and hypothyroidism?
Can you have both hyperthyroidism and hypothyroidism?
Can hypothyroidism be converted to hyperthyroidism?
Related content

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 symptoms of each condition, main causes, treatment options, and more.

Let’s start by taking a look at symptoms of hypothyroidism vs. hyperthyroidism.

What are the signs and symptoms of hyperthyroidism and hypothyroidism?

Before highlighting hypothyroidism and hyperthyroidism symptoms, let’s do a quick review of each of these conditions. If you have hypothyroidism, or an underactive thyroid, your thyroid gland fails to produce sufficient hormones to meet your body’s needs. On the other hand, hyperthyroidism is also called overactive thyroid because with this condition your thyroid produces too much of the thyroid hormone called thyroxine (T4).

While both these conditions are related to the way your thyroid functions, they each produce different symptoms in your body (although there are some overlapping symptoms between the two conditions). Here, we’ll dive deeper into each of these kinds of thyroid conditions.

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 aches or weakness
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)

So if you have unexplained weight gain, fatigue or other hypothyroidism symptoms, you may want to take the Everlywell at-home Thyroid Test to see if your thyroid hormone levels are balanced.

And fortunately, with a diagnosis from a healthcare provider, you can receive effective treatments for your hypothyroidism.

Cause 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 your thyroid gland.

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.

Treating hypothyroidism: 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.

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.

If you have 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
Weak muscles
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 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. 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 towards an overactive gland, discuss your next-step options with your healthcare provider. In many cases, thyroid hormone balance can be restored by simply adjusting medication levels.

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

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