While an underactive thyroid can cause a slew of problems, so can the opposite issue. Your thyroid can be too active, a condition known as hyperthyroidism. When your thyroid is overactive, everything speeds up: Your heart beats faster, you sweat more, and you may lose weight for no apparent reason. You might also feel nervous or irritable.
About 1.2 percent of the U.S. population has hyperthyroidism, most often due to Graves' disease. Another autoimmune disorder, Graves' causes your immune system to mistakenly attack the thyroid and prompt it to make too much thyroid hormone. Other causes include an inflammation of the thyroid or the presence of a thyroid nodule (a small and usually benign bump).
It's also possible for someone who started out with an underactive thyroid to end up with an overactive one if they take too much synthetic thyroid hormone. That kind of flip can be corrected by adjusting your dose, assuming you're not deliberately overdoing it in an effort to lose weight (not a smart idea).
If you or your doctor think you might have hyperthyroidism, you'll need blood tests. You'll be diagnosed with this issue if your TSH is low yet your free T4 is high.
Most people with hyperthyroidism are initially treated with a medication like methimazole or PTU. These drugs interfere with the production of thyroid hormone so you start making less, but you can only take them for a maximum of 18 months, says Dr. Jaggi."They can cause liver injury and make you more prone to infection," she explains.
Some people go into remission within that time period, but if you still need treatment then the next step is to swallow a radioactive iodine pill. "The thyroid is the only place in the body with receptors for iodine, so it ablates any thyroid cells," says Dr. Jaggi. Most patients then become hypothyroid within the next six months, and when that happens you'll need to start on synthetic thyroid hormone.
In rare cases—like when someone is having very severe symptoms and can't wait half a year for the radioactive iodine to kick in—doctors will perform surgery to remove the entire thyroid.
Whatever treatment you end up requiring, a knowledgeable endocrinologist should be able to help you get your hormone levels balanced so that you can feel your best.