Liothyronine is the most potent form of thyroid hormone. Its medical use is as the sodium salt of triiodothyronine (T3), which is chemically similar and pharmacologically equivalent to T3. As such, it acts on the body to increase basal metabolic rate, affect protein synthesis, and increase the body's sensitivity to catecholamines (such as epinephrine) by binding to thyroid receptors within cells. As monotherapy or in combination therapy with SSRIs, liothyronine may also promote new neuron formation in the central nervous system. Thyroid hormones are essential for the proper development and differentiation of all cells in the human body. These hormones also regulate protein, fat, and carbohydrate metabolism and affect how human cells use their energy reserves.
Thyroid hormones are well absorbed orally. Liothyronine is almost completely absorbed and absorption is not affected by food intake. Liothyronine exhibits very high binding to plasma proteins. This is approximately 99.7% of the administered dose. Liothyronine is metabolized mainly in the liver, where it is deiodinated to diiodothyronine and monoiodothyronine, followed by conjugation with glucuronides and sulfates. The main excretion of thyroid hormones is through the kidneys. The half-life of liothyronine is about 1 to 2 days.