One of the most common prescription drugs in America – levothyroxine – is used by people with underactive thyroid glands, also known as hypothyroidism. However, a new study by Mayo Clinic researchers says the majority of people were initiated on levothyroxine for mild subclinical hypothyroidism or for no apparent thyroid dysfunction. These results, published in JAMA Internal Medicine, suggest significant overuse of levothyroxine.

Mayo researchers and colleagues examined retrospective, deidentified case data using the OptumLabs Data Warehouse, which includes insured and Medicare Advantage patients. For the ten years between 2008 and 2018, 58,706 patients began using levothyroxine and have full thyroid tests available before initiation. Among these patients, about half started levothyroxine for mild subclinical hypothyroidism and about a third started without the evidence of thyroid dysfunction.

The researchers stated that “Frequent initiation of levothyroxine in patients with mild subclinical hypothyroidism is at odds with evidence demonstrating no significant impact of levothyroxine replacement on measures of health-related quality of life, thyroid-related symptoms, depressive symptoms, fatigue or cognitive function.”

Juan P. Brito, M.D.

“Our data also suggest that a significant proportion of adults initiating levothyroxine do so when thyroid hormone levels are within the normal range,” says Juan P. Brito, M.D., Mayo Clinic endocrinologist and first author of the study. “Since this is the first study to describe this potentially inappropriate levothyroxine use, our findings need to be corroborated by subsequent studies.”

Dr. Brito also says that patients taking levothyroxine need to accommodate into their routine taking the pill 30–60 min before a meal, monitoring the effects, and complying with clinic and laboratory visits to titrate the dose. He mentioned that some studies have estimated that the treatment and monitoring amount to about $1600 to $1800 a year for a typical patient on levothyroxine.

The researchers say their results suggest substantial overuse of levothyroxine during the entire duration of the study, meaning there are significant opportunities to improve care. For instance, Dr. Brito suggests revising the current guideline recommendations for the use of levothyroxine for patients with mild subclinical hypothyroidism and to educate clinicians about the lack of effect of levothyroxine in patients without any evidence of thyroid dysfunction.

The study was supported by Mayo Clinic's Robert D. and Patricia E. Kern Center for the Science of Health Care Delivery.