thy·​rox·​ine | \ thī-ˈräk-ˌsēn How to pronounce thyroxine (audio) , -sən \
variants: or thyroxin

Definition of thyroxine

: an iodine-containing hormone C15H11I4NO4 that is an amino acid produced by the thyroid gland as a product of the cleavage of thyroglobulin, increases metabolic rate, and is used to treat thyroid disorders

called also T4

Examples of thyroxine in a Sentence

Recent Examples on the Web Treatment for hypothyroidism involves taking a daily dose of a synthetic replacement for thyroid hormone (thyroxine or T4) called levothyroxine. Mathew Devine, SELF, 23 May 2022 Hyperthyroidism, for example, occurs when the thyroid gland produces too much of the hormone thyroxine, according to the Mayo Clinic. Valerie Pavilonis, USA TODAY, 31 Mar. 2022 Thyroid replacement, usually with thyroxine, the identical hormone made by the thyroid, is effective at returning blood hormone levels to normal and reversing any symptoms. Dr. Keith Roach, oregonlive, 30 Nov. 2021 It’s when thyroxine is high that the heart can be damaged, particularly by the development of atrial fibrillation. Dr. Keith Roach, oregonlive, 12 Aug. 2021 The hormones that the thyroid gland makes — triiodothyronine, or T3, and thyroxine, or T4 — affect all aspects of your metabolism. Mayo Clinic News Network,, 4 Oct. 2019 Your thyroid produces hormones like thyroxine and triiodothyronine, which influence many of your body’s systems, according to the Mayo Clinic. Zahra Barnes, SELF, 16 Jan. 2018 About 3 million French people, 80% of them women, take Levothyrox, which replaces the hormone thyroxine in patients with hypothyroidism. Yves Sciama, Science | AAAS, 27 Sep. 2017 Taken by about 3 million people in France alone, the drug replaces the hormone thyroxine in patients with the metabolic condition, hypothyroidism. Beth Mole, Ars Technica, 4 Oct. 2017 See More

These example sentences are selected automatically from various online news sources to reflect current usage of the word 'thyroxine.' Views expressed in the examples do not represent the opinion of Merriam-Webster or its editors. Send us feedback.

First Known Use of thyroxine

1918, in the meaning defined above

History and Etymology for thyroxine

alteration (by substitution of the suffix -ine entry 2 for -in entry 1) of earlier thyroxin, shortened from thyro-oxy-indol, from thyro- + oxy + indole

Note: The name was introduced by the American biochemist Edward Calvin Kendall (1886-1972) in "The thyroid hormone and its relation to the other ductless glands," Endocrinology, vol. 2 (1918), p. 90. The change of suffix was made when it was realized that the compound had an amino acid as a nucleus rather than indole, as Kendall had believed. (See A.T. Cameron, "Designation of thyroxine," Nature, vol. 119, June 25, 1927, p. 925.)

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The first known use of thyroxine was in 1918

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Dictionary Entries Near thyroxine

thyrotropin-releasing hormone



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Cite this Entry

“Thyroxine.” Dictionary, Merriam-Webster, Accessed 17 Aug. 2022.

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More Definitions for thyroxine


variants: or thyroxin \ thī-​ˈräk-​ˌsēn, -​sən How to pronounce thyroxine (audio) \

Medical Definition of thyroxine

: an iodine-containing hormone C15H11I4NO4 that is an amino acid produced by the thyroid gland as a product of the cleavage of thyroglobulin, that increases the metabolic rate, and that is used to treat thyroid disorders

called also T4

More from Merriam-Webster on thyroxine Encyclopedia article about thyroxine


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