L-Thyroxine sodium salt pentahydrate, also known as Levothyroxine, is a synthetic hormone utilized in the study of hypothyroidism. It is biologically activated into Triiodothyronine (T3) from its original form, L-Thyroxine (T4), through conversion by DIO enzymes.

Liothyronine Sodium is the sodium salt form of liothyronine, a synthetic form of the levorotatory isomer of the naturally occurring thyroid hormone triiodothyronine (T3). Liothyronine sodium (3,3',5-Triiodo-L-thyronine sodium) binds to nuclear thyroid receptors which then bind to thyroid hormone response elements of target genes. As a result, liothyronine sodium induces gene expression that is required for normal growth and development. Liothyronine sodium is more potent and has a more rapid action than thyroxine (T4).