Factitious hyperthyroidism is the presence of excessive thyroid hormone levels, caused by taking too much thyroid hormone medication.

The thyroid gland produces the hormones thyroxine (T4) and triiodothyronine (T3). In most cases of hyperthyroidism, the thyroid gland itself produces too much of these hormones.

However, hyperthyroidism can also be caused by taking too much thyroid hormone medication for hypothyroidism. This is called factitious hyperthyroidism. When this occurs because the prescribed dose of hormone medication is too high, it is called iatrogenic, or "doctor-induced," hyperthyroidism.

Factitious hyperthyroidism can also occur when a patient intentionally takes too much thyroid hormone. People with psychiatric disorders such as Munchausen syndrome, people attempting to lose weight and those seeking fraudulent insurance compensation sometimes misuse thyroid hormone. Children occasionally ingest thyroid hormone pills accidentally.

In rare cases, factitious hyperthyroidism has been found to be caused by eating meat contaminated with thyroid gland tissue.

The symptoms of factitious hyperthyroidism are identical to the symptoms of hyperthyroidism caused by the thyroid gland, with the following exceptions:

• There is no goiter. The thyroid gland is usually small.
• The eyes do not protrude, as they do in Graves' disease (the most common type of hyperthyroidism).
• The skin over the shins does not thicken, as it occasionally does with people with Graves' disease.

The following test results may indicate factitious hyperthyroidism:

• Low levels of TSH
• High levels of total T4
• High levels of free T4
• High levels of total T3
• Low levels of thyroglobulin
• Low radioactive iodine uptake