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Biological: Behavioural genetics · Evolutionary psychology · Neuroanatomy · Neurochemistry · Neuroendocrinology · Psychoneuroimmunology · Physiological Psychology · Psychopharmacology

Identifiers
style="background: #F8EABA; text-align: center;" colspan="2"	Thyroxine
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CAS number	7488-70-2
PubChem	853
MeSH	Thyroxine
SMILES	NC(Cc1cc(I)c(Oc2cc(I)c(O) c(I)c2)c(I)c1)C(O)=O
Properties
Molecular formula	C₁₅H₁₁I₄NO₄
Molar mass	776.87
Hazards
style="background: #F8EABA; text-align: center;" colspan="2"	Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) Infobox disclaimer and references

Thyroxine, or 3,5,3',5'-tetraiodothyronine (often abbreviated as T₄), a form of thyroid hormones is the major hormone secreted by the follicular cells of the thyroid gland.

T₄ is transported in blood, with 99.95% of the secreted T₄ being protein bound, principally to thyroxine-binding globulin (TBG), and, to a lesser extent, to transthyretin and serum albumin. T₄ is involved in controlling the rate of metabolic processes in the body and influencing physical development.

Note: Thyroxine is a prohormone and a reservoir for the active thyroid hormone triiodothyronine (T₃). T₄ is converted in the tissues by deiodinases to T₃. The "D" isomer is called "Dextrothyroxine"^[1] and is used as a lipid modifying agent.^[2] The half-life of thyroxine once released into the blood circulatory system is about 1 week.

The hormone was synthesised in 1927 by British chemists Charles Robert Harington and George Barger.