by Isabella Backman, Yale University Credit: Pixabay/CC0 Public Domain As many as 90% of those who take levothyroxine [Synthroid] may have been unnecessarily prescribed the hypothyroidism medication. Approximately 23 million Americans take levothyroxine, making it one of the most prescribed drugs in the country. To test for hypothyroidism (underactive thyroid), clinicians measure the levels of...