What it is
A synthetic form of the thyroid hormone thyroxine (T4) available as oral tablets, capsules, and an oral solution.
How it works
Synthetic T4 is converted peripherally to the more active triiodothyronine (T3); both bind nuclear thyroid hormone receptors to regulate gene transcription affecting metabolism, growth, and development.
Where it's used
Used as replacement therapy in primary, secondary, and tertiary hypothyroidism and in the suppressive management of thyroid cancer.
FDA-approved use
Hypothyroidism (all forms) and as an adjunct to surgery and radioiodine therapy in the management of thyrotropin-dependent well-differentiated thyroid cancer.
Tracking it
Levothyroxine is oral, which makes consistency the whole game — a simple daily check-off with a reminder beats memory every time. with a half-life of about 7 days (168 h), a dose log also lets a tracker model the relative amount still in your system between doses.
Source
OpenFDA
Last reviewed 2026-06-11