Causes of Overactive Thyroid

Silent Thyroiditis
This type of thyroiditis is called "silent" because it is painless, as is postpartum thyroiditis, even though the thyroid may be enlarged. Like postpartum thyroiditis, silent thyroiditis is believed to be an autoimmune condition and sometimes develops into permanent hypothyroidism.

Causes Outside the Thyroid Gland

The following sections discuss overactive thyroid causes that can start outside of the thyroid gland.
Iodine-Induced Overactive thyroid
The thyroid gland uses iodine to make thyroid hormone, so the amount of iodine a person consumes influences the amount of hormone their thyroid makes. In some people, consuming large amounts of iodine may cause the thyroid to make excess thyroid hormone.
Sometimes, significant amounts of iodine are contained in medications (such as amiodarone, which is used to treat heart problems) or in supplements containing seaweed. Some cough syrups also contain large amounts of iodine. Large amounts of iodine may also be used for certain procedures, such as coronary angioplasty or computed tomography (CT) scans.
Too Much Thyroid Hormone
Some people who take synthetic thyroid hormone replacement therapy (levothyroxine, Levoxyl®, Synthroid®, Levothroid®, Tirosint®, or Unithroid®) for hypothyroidism may take too much. In other cases, people with thyroid cancer may be given synthetic thyroid hormones to minimize the effects of TSH on tumor growth. Whatever the reason, it is possible for a person to take too much synthetic hormone replacement therapy.
People taking synthetic thyroid hormone should see their healthcare provider at least once a year to have their thyroid hormone levels checked and should carefully follow their healthcare provider's instructions about the dose they take.
Some medications can interact with synthetic thyroid hormone to raise levels in the blood. Ask your healthcare professional about drug interactions when starting or stopping new medications.
Last reviewed by: Arthur Schoenstadt, MD
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