While it is unlikely, a person may alternate between hyperthyroidism and hypothyroidism. This depends on the balance of thyroid antibodies present in autoimmune thyroid disorders.

The thyroid is a butterfly-shaped gland at the base of the front of a person’s neck. It secretes hormones that help to control vital body functions.

Hypothyroidism happens when the thyroid does not produce enough hormones, while hyperthyroidism occurs when the thyroid produces too much hormone.

The most common cause of these thyroid disorders is autoimmune diseases. In these diseases, a person’s own immune system attacks the thyroid gland, causing it to produce too many or too few hormones.

A person may experience fluctuating hyperthyroidism and hypothyroidism due to an imbalance between thyroid antibodies in thyroid immune disorders.

This article explores whether hypothyroidism and hyperthyroidism can occur together. It also discusses the main differences between the two conditions.

A note about sex and gender

Sex and gender exist on spectrums. This article will use the terms “male,” “female,” or both to refer to sex assigned at birth. Click here to learn more.

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The most important distinction between hypothyroidism and hyperthyroidism is the thyroid gland’s hormone output.

Hypothyroidism is when the thyroid gland is underactive and does not make enough thyroid hormones for the body. Meanwhile, hyperthyroidism occurs in hyperactive thyroid glands that produce too many hormones.

Learn more about common thyroid disorders.

A lack of thyroid hormones causes certain bodily processes to slow down, while too many hormones speed them up. Below are some of the symptoms associated with each condition:

Learn more about the symptoms of hypothyroidism.

A person’s body cannot have hypothyroidism and hyperthyroidism at the same time.

Each condition depends on the level of thyroid hormones in the body, and the thyroid gland cannot underproduce and overproduce thyroid hormones simultaneously.

However, it is possible for a person to transition or switch between the two conditions, as explained below.

While it is extremely rare, some people may experience oscillating hypothyroidism and hyperthyroidism. This is due to the production of two thyroid hormone receptor (TSHR) antibodies:

  • Thyroid-stimulating antibody (TSAb): This antibody can be responsible for an overactive thyroid gland when it activates TSHRs.
  • Thyroid-stimulating hormone blocking antibody (TBAb): This antibody can be responsible for hypothyroidism when it blocks thyroid-stimulating hormones (TSH) from binding to TSHRs.

Both TSHR antibodies may coexist in the body, and a person’s thyroid function depends on the balance between these two antibodies.

While rare, a shift from one to the other condition may occur spontaneously. Other times, specific treatments for one condition may lead to the development of the other.

Some treatments can alter the level of thyroid antibodies and the balance between the two, causing a person to swing from hyper- to hypothyroidism and vice versa. These include antithyroid treatment and thyroid hormone replacement therapy.

In 2018, researchers presented a case study of a person who had spontaneously oscillating thyroid function for 15 years. Several years after the initial diagnosis of hyperthyroidism, the person spontaneously switched to hypothyroidism, to which the doctor gave thyroid hormone replacement as treatment. After 8 years, the person’s hyperthyroidism returned.

Similarly, a 2019 case report presented a rare case of an individual spontaneously converting from Hashimoto’s thyroiditis to Graves’ disease. The individual opted for treatment with antithyroid medication.

An 18-year-old male who had five cycles of alternating hypothyroidism and hyperthyroidism over 17 months had a total thyroidectomy due to difficulty managing the condition with antithyroid medications.

Another report from 2021 presented an adolescent who switched from hyperthyroidism and hypothyroidism due to a combination of Graves’ disease and Hashimoto’s thyroiditis.

Treatments for this combination of conditions may include surgery and radioactive iodine. These could help a person avoid switches in thyroid function and the frequent need to change medications. However, doctors can only perform these treatments while a person is in the hyperthyroid phase.

Most cases of switching from hyperthyroidism to hypothyroidism occur several years after a person stops using antithyroid medications.

A 2022 study reports a rare case of a person initially diagnosed with hypothyroidism switching to Graves’ disease.

A similar case study reported a 61-year-old person transitioning to Graves’ disease after a doctor diagnosed hypothyroidism approximately 3 decades previously and prescribed levothyroxine replacement therapy.

The authors of the study suspected that an upper respiratory tract infection was the environmental trigger for the switch.

Some research indicates that it is common for people with Graves’ disease to convert to a hypothyroid state after radioactive iodine treatment or in end-stage Graves’ disease. These individuals may require lifelong thyroid hormone replacement therapy.

People with alternating hypothyroidism and hyperthyroidism may manage the conditions with their doctor’s guidance.

However, multiple case studies indicate that switching tends to recur, and surgery or radioactive iodine may be necessary for a person to manage this complex combination of conditions.

A person should speak with a doctor for further advice about managing hypothyroidism and hyperthyroidism.

It is not possible for a person to have both hypothyroidism and hyperthyroidism simultaneously.

However, a person with an autoimmune thyroid disorder may have an oscillating thyroid function. This is when a person experiences alternating periods of hyper- and hypothyroidism.

This may occur spontaneously or as a result of specific treatments, such as antithyroid medication or thyroid hormone replacement therapy.

People with alternating hypothyroidism and hyperthyroidism should speak with a healthcare professional for further guidance.