Why carry out this study?

Hypothyroidism is common in the USA and can be clinically overlooked but, nevertheless, is associated with a variety of adverse clinical outcomes.

Clinical guidelines recommend levothyroxine (LT4) as the standard of care for hypothyroidism and that patients should be treated with a consistent preparation of synthetic levothyroxine without switching among formulations.

This study examined clinical outcomes (TSH laboratory values out of recommended ranges and diagnoses of comorbidities) between two cohorts of patients with hypothyroidism, one treated continuously with Synthroid® and the other that switched to an alternative LT4 formulation.

What was learned from the study?

Among insured adults in the USA with hypothyroidism who had initial stable treatment with Synthroid®, people who were switched to an alternative LT4 formulation tended to be older, more likely to be male, and less likely to have had a visit to an endocrinologist’s office than those who were treated continuously with Synthroid®.

Switching to an alternative LT4 formulation was associated with a higher likelihood of a TSH laboratory value outside of the target range in the post-period as compared to continuous use of Synthroid®.

Compared to continuous treatment, switching was associated with higher likelihoods of being diagnosed with a number of negative clinical outcomes: chronic kidney disease, depression, fatigue, hypertension, or obesity as well as a composite clinical endpoint.