Liothyronine (T3)

Overview

Liothyronine (T3) is the biologically active form of thyroid hormone, produced from thyroxine (T4) via deiodination in peripheral tissues. It binds nuclear thyroid hormone receptors and regulates metabolism, thermogenesis, cardiac function, cognition, and body composition. T3 has a short half-life of 3–4 hours, requiring multiple daily dosing for stable levels. Clinical uses include hypothyroidism (particularly T4-to-T3 conversion disorders where T4 monotherapy is insufficient) and suppression therapy in thyroid cancer. A common conversion problem involves excessive production of reverse T3 (rT3), which blocks T3 receptor sites without activating them, causing hypothyroid symptoms despite normal lab values. Co-factors critical for optimal T4→T3 conversion include selenium (deiodinase enzymes), iodine, zinc, and iron. Stack interactions: T3 increases the clearance rate of many supplements and drugs; potentiates cardiac effects of stimulants; may alter insulin requirements.

Dosage

See product label · Morning · Can take on empty stomach

Scientific Sources

• Treatment Preferences in Patients With Hypothyroidism. (J Clin Endocrinol Metab, 2025 Feb 18)
• Comparative Effectiveness of Levothyroxine, Desiccated Thyroid Extract, and Levothyroxine+Liothyronine. (J Clin Endocrinol Metab, 2021 Oct 21)
• Treatment of hypothyroidism with levothyroxine plus slow-release liothyronine. (Trials, 2025 Jul 1)
• Phase NA | UNKNOWN | Effect of Dietary Supplements on Levothyroxine Absorption in Pregnancy
• Phase NA | NOT_YET_RECRUITING | Changes in Natural Immunity in Pregnant Women With Autoimmune Thyroid Disease
• FDA approved | Cytomel (Liothyronine) | NDA010379
• pubmed_ncbi_api
• pubmed_ncbi_api
• PubChem Compound 5920

Frequently Asked Questions