This study compares two different brands of thyroxine (thyroid hormone). Currently, pharmacists may be substituting generic formulations of thyroid hormone without your doctor knowing about this. Although a small difference in thyroid function is not significant in most healthy children, adolescents and adults, in infants and toddlers even a small difference in thyroid function can have important harmful consequences on brain development. The purpose of the present study is to learn whether the difference between brands of thyroid hormone that are currently being substituted is sufficient to cause a difference in thyroid function.

This study is an unblinded, randomized controlled cross-over study, which involves taking 2 different forms of levothyroxine sequentially over a 16 week period. Subjects will have a total of 3 visits over this time period. At the first visit, subjects are randomized to receive either generic (Sandoz) levothyroxine or Synthroid (Abbott) brand of levothyroxine. Blood is drawn for baseline thyroid function studies and other markers which are influenced by thyroid hormone at each visit. The second visit is the cross-over visit, and the final visit is a close-out visit, after which each subject will resume taking their previous formulation of levothyroxine.

• Congenital Hypothyroidism
• Hypothyroidism

Inclusion Criteria:

• Age between 3 and 18 years
• Diagnosis of Congenital Hypothyroidism with initial TSH > 100
• Ability to understand directions and follow all instructions

Exclusion Criteria:

• Not on any drug interfering with absorption of levothyroxine