One of the common symptoms of hyperthyroidism is weight loss. However, not all people with hyperthyroidism will lose weight.

The thyroid is a small gland in front of the windpipe in the neck. It produces hormones that help manage certain bodily functions, including:

  • heart rate
  • metabolism
  • body temperature regulation

If a person’s thyroid produces too many hormones, doctors refer to this as hyperthyroidism, or an overactive thyroid.

Some possible symptoms of hyperthyroidism include:

This article explores whether it is possible to have overactive thyroid without weight loss, how thyroid function affects weight, and what can cause weight gain in hyperthyroidism. It also discusses the causes of hyperthyroidism and when to contact a doctor.

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In the United States, approximately 1 in 100 people over 12 years have an overactive thyroid. A common symptom of hyperthyroidism is weight loss. People with an overactive thyroid may lose weight even though they experience an increased appetite.

Hyperthyroidism can cause weight loss as a result of a fast metabolism. A sped-up metabolism can also cause a rapid heartbeat, another symptom of an overactive thyroid.

However, symptoms can vary from person to person. Not everyone with hyperthyroidism will experience weight loss.

A 2019 review suggests that 10% of people with hyperthyroidism may gain weight. Weight gain may occur as a result of treatment or increased appetite.

The thyroid gland releases thyroid hormone, which is responsible for various functions, including regulating metabolism.

Metabolism is an essential process that breaks down food and drink in the body into energy.

When the thyroid gland does not work correctly, it may impair metabolic function. For people with overactive thyroid, metabolism may be high or fast, meaning a person will burn more calories than usual.

Therefore, a person may lose weight more quickly with a high metabolism.

In contrast, people with an underactive thyroid, or hypothyroidism, may have a slow metabolism. A person with a slow metabolism is more likely to experience weight gain as they cannot burn calories as quickly, causing the body to store excess fat.

Weight gain may occur in hyperthyroidism as a result of an increased appetite.

However, weight loss generally results from the treatment a person may receive for the condition.

Treatment involves bringing a person’s hormone levels back in the typical range. This may initially cause a person to put weight back on.

Some of the treatment options for overactive thyroid include:

Antithyroid drugs

Doctors may prescribe thionamides, or antithyroid drugs, to treat hyperthyroidism. Thionamides block the thyroid gland from making too much of the thyroid hormone.

Common examples include methimazole and propylthiouracil. A pregnant person is most likely to receive propylthiouracil, as methimazole may harm the fetus.

However, these antithyroid medications may block the thyroid hormone too much, which can result in weight gain.

Radioiodine therapy

This is a type of radiation therapy that destroys the cells that cause hyperthyroidism.

A person usually takes this as a drink or capsule. The formula contains iodine and a low dose of radiation.

Almost everyone who has radioiodine therapy will later develop hypothyroidism. Radioiodine therapy causes the thyroid to not produce enough thyroid hormone, potentially leading to weight gain.

However, hypothyroidism is easier to treat than hyperthyroidism.

According to a 2022 study involving people with Graves’ disease, a condition that causes overactive thyroid, those receiving radioiodine therapies were most likely to experience weight gain.

Learn more about radioiodine therapy.


Doctors rarely recommend surgery as a treatment option for hyperthyroidism.

Surgery often occurs as a last resort for people with swelling in their thyroid gland, those with eye issues due to hyperthyroidism, or for pregnant individuals who cannot take antithyroid medications.

The surgery involves the removal of part of the thyroid gland. However, in some cases, surgeons will take out the entire gland. This removal can stop hyperthyroidism from returning.

A 2020 systematic review and meta-analysis suggests that those who have had thyroid removal surgery may experience mild weight gain. The researchers say this is most common in younger people.

When a person has part of their thyroid removed, they can develop hypothyroidism and they may put on weight. A person who no longer has a thyroid gland will need to take medication for the rest of their life.

Some of the possible causes of hyperthyroidism include:

  • Graves’ disease
  • overactive thyroid nodules
  • thyroiditis, or inflammation of the thyroid gland
  • having too much iodine
  • having too much thyroid hormone medication
  • benign tumors in the pituitary gland

A person may also develop hyperthyroidism during pregnancy. This is because they may have high levels of human chorionic gonadotropin, a substance that can develop during early pregnancy.

A person should consult a doctor if they experience the symptoms of hyperthyroidism, such as:

A doctor may order a blood test to help identify whether an overactive thyroid is present.

Hyperthyroidism is a condition where the thyroid gland produces too much thyroid hormone. This can affect metabolism and often results in unexplained weight loss.

However, not everyone will experience weight loss as a result of hyperthyroidism. Some may experience the opposite due to an increase in appetite or as a result of hyperthyroidism treatment.

A person should consult a doctor if they have symptoms of hyperthyroidism.