Starting estrogen for a patient on levothyroxine may necessitate what adjustment?

When a patient begins estrogen therapy while on levothyroxine, an adjustment in the dosage of levothyroxine may be necessary because estrogen can increase the levels of thyroxine-binding globulin (TBG) in the blood. This rise in TBG can lead to increased binding of thyroid hormones, potentially causing a decrease in the free fraction of thyroid hormone available in the body, which may result in a lower effective dose of circulating thyroid hormone.

As a response to this change, healthcare providers often consider increasing the dose of levothyroxine. The goal is to restore the balance of free thyroid hormones to ensure that the patient's thyroid function remains optimal. Careful monitoring of thyroid hormone levels is essential after initiating estrogen therapy to determine if additional adjustments to the levothyroxine dosage are warranted.