Levothyroxine is a synthetic form of the thyroid hormone thyroxine (T4), widely used to treat hypothyroidism, a condition in which the thyroid gland produces insufficient hormones. Chemically identical to the naturally occurring hormone, levothyroxine helps restore normal metabolism, growth, and energy balance in patients with thyroid hormone deficiency. The therapeutic use of thyroid extracts dates back to the late 19th and early 20th centuries, but levothyroxine as a purified, standardized synthetic hormone was first introduced in the 1950s, providing a safer and more consistent alternative to animal-derived thyroid preparations. Over the decades, levothyroxine has become the gold standard for thyroid hormone replacement therapy worldwide, valued for its efficacy, predictable pharmacokinetics, and ability to normalize thyroid function with once-daily dosing. Its history reflects the evolution of endocrinology from crude extracts to precise, modern hormone replacement therapies.
