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Structural formula
Structural formula of L-thyroxine
Non-proprietary name Levothyroxine
other names
  • L - (-) - thyroxine
  • ( S ) -thyroxine
  • Tetraiodothyronine
  • 3,3 ', 5,5'-tetraiod- L- thyronine
  • 2-Amino-3- [4- (4-hydroxy-3,5-diiodophenoxy) -3,5-diiodophenyl] propanoic acid
Molecular formula
  • C 15 H 11 I 4 NO 4 (levothyroxine)
  • C 15 H 10 I 4 NNaO 4 (levothyroxine sodium salt )
External identifiers / databases
CAS number
  • 7488-70-2 ( DL -hyroxine)
  • 51-48-9 (levothyroxine)
  • 55-03-8 (levothyroxine sodium salt )
PubChem 853
ChemSpider 8402
Wikidata Q216852
Drug information
ATC code

H03 AA01

Molar mass 776.87 g · mol -1 (levothyroxine)
Physical state


Melting point

231–233 ° C (levothyroxine)


slightly soluble in water (0.105 µg l −1 at 25 ° C)

safety instructions
Please note the exemption from the labeling requirement for drugs, medical devices, cosmetics, food and animal feed
GHS labeling of hazardous substances
no GHS pictograms
H and P phrases H: no H-phrases
P: no P-phrases
Toxicological data
  • 20 mg kg −1 ( LD 50ratip , levothyroxine sodium salt)
  • 50 mg kg −1 ( LD 50ratsc , levothyroxine sodium salt)
As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions .

Thyroxine ( T 4 , 3,3 ', 5,5'-Tetraiod- L -thyronine , like Latin Glandula thyr [e] oidea and Thyreoidea , " thyroid ", from ancient Greek θυρεοειδής , thyreoeides ' shield-like') is a hormone that is formed in the thyroid gland in mammals.

Thyroxine is a non-proteinogenic α- amino acid with the empirical formula C 15 H 11 I 4 NO 4 . Thyroxine is the prohormone to triiodothyronine , T 3 for short (three iodine atoms in the molecule). These thyroid hormones are essential for energy metabolism and important partners for many other hormones such as B. Insulin , Glucagon , Somatotropic Hormone and Adrenaline . The superordinate regulating hormone is the thyroid stimulating hormone (TSH).

Thyroxine is chiral . The natural substance is L- thyroxine [synonym: ( S ) -hyroxine]. If “Thyroxine” is mentioned in the following text and in the scientific literature without any additional name ( prefix ), L- thyroxine is always meant.

History, isolation and synthesis

Edward Calvin Kendall isolated thyroxine for the first time from dried thyroid preparations in 1914/1915. Charles Robert Harington characterized and synthesized it for the first time in 1926. In the same year, Thyroxin was marketed by Georg Friedrich Henning for the treatment of thyroid disorders under the name "Thyroxin Henning".

Chemical properties

The thyroxine molecule contains four iodine atoms (tetraiodothyronine), hence the name T 4 . In the body, thyroxine - bound to thyroxine-binding globulin - has a half-life of around eight days.


For the detection of thyroxine in the serum and for therapy control are enzyme immunological and radio immunological methods. The coupling of HPLC with mass spectrometry is also used for special analytical questions.

Therapeutic use

Thyroxine is used to treat an underactive thyroid ( hypothyroidism ). Patients with this disease usually need hormone replacement for life. Thyroxine is taken as a tablet on an empty stomach at least 30 minutes before breakfast in order to optimize the absorption of the hormone in the intestine, which tends to be difficult to absorb. The dose in humans is usually between 12.5 µg and 200 µg per day. An intravenous form of thyroxine is also available for treating severe hypothyroid coma .

In addition to its use in hypothyroidism, thyroxine can be used to supplement an adequate iodine supply for the treatment of goiter ( goiter ). In addition, the thyroxine administration serves to suppress the thyrotropic control circuit - either diagnostically with the suppression scintigraphy or therapeutically in the case of resected malignant thyroid tumors to prevent recurrences . In hyperthyroidism , the administration of thyroxine is contraindicated, except for special, rarely used treatment strategies ( block and replace ).

Thyroxine is also misused as a slimming pill . There is no approval or proof of effectiveness for this indication. The administration of thyroid hormone can increase the energy expenditure, but this can be compensated for by increased food intake. In addition, thyroid hormones promote insulin resistance in the event of an overdose , the cardiovascular system is more stressed, and the risk of osteoporosis increases, especially in postmenopausal women . Overdose deaths are known.

Thyroxine and triiodothyronine also play a role in enhancing the effect and phase prophylaxis for the treatment of depression.

With an intake of thyroxine or thyronine should thyrotropin value ( TSH ) are monitored regularly. This is especially true in the setting phase and when changing the dose.

Thyroxine preparations from different manufacturers can differ considerably in terms of their bioavailability , which is why changing the commercial preparation is not recommended if the previous preparation is tolerated.

Comprehensive studies on the pharmacoepidemiology of thyroxine preparations were presented by the Robert Koch Institute . Thyroxine is one of the five most commonly prescribed drugs in the world.

Trade names

in alphabetic order


As tablets:

Berlthyrox (D), Eferox (D), Eltroxin (CH), Euthyrox (A, CH, D), Eutirox (D), L-Thyrox (D), L-Thyroxine (D), Levothyroxine (A, D), Prothyreo (D), Tirosint (CH), Thyrex (A)

As a drop:

Eferox (D), L-Thyroxine (D), Levothyroxine (D)

Combination preparations

With triiodothyronine :

Novothyral (A, CH, D), Prothyrid (D), Thyreocomb (D)

With potassium iodide :

Eferox Jod (D), Jodthyrox (D, A), L-Thyrox Jod (D), L-Thyroxin Jod (D), Thyronajod (D)


Web links

Individual evidence

  1. ^ A b Charles Robert Harington: Chemistry of Thyroxine. I. Isolation of Thyroxine from the Thyroid Gland. In: Biochem. J. 20 (2), 1926, pp. 293-299. PMID 16743658 ; PMC 1251713 (free full text).
  2. Entry on thyroxine in the ChemIDplus database of the United States National Library of Medicine (NLM) .
  3. a b Data sheet L-Thyroxine, ≥98% (HPLC) from Sigma-Aldrich , accessed on November 18, 2019 ( PDF ).
  4. ^ A b Axel Kleemann , Jürgen Engel, Bernd Kutscher, Dieter Reichert: Pharmaceutical Substances. 5th edition. Thieme-Verlag, Stuttgart 2009, ISBN 978-3-13-558405-8 , pp. 802-804; also online with biannual additions and updates.
  5. S. Silbernagl, A. Despopoulos: Pocket Atlas of Physiology. 4th edition. Thieme-Verlag, 1991.
  6. ^ EC Kendall: Isolation of the iodine compound which occurs in the thyroid . In: The Journal of Biological Chemistry . tape 39 , 1919, pp. 125-147 ( [PDF]).
  7. ^ Charles Robert Harington: Chemistry of Thyroxine. II. Constitution and Synthesis of Desiodo-Thyroxine. In: Biochem. J. 20 (2), 1926, pp. 300-313. PMID 16743659 ; PMC 1251714 (free full text).
  8. ^ Charles Robert Harington, George Barger: Chemistry of Thyroxine. III. Constitution and Synthesis of Thyroxine. In: Biochem. J. 21 (1), 1927, pp. 169-183. PMID 16743801 ; PMC 1251886 (free full text).
  9. TL Williams, J. Archer: Validation of an automated enzyme immunoassay for the measurement of serum total thyroxine in cats. In: Vet Clin Pathol. 45 (1), Mar 2016, pp. 148–153. PMID 26840919
  10. LA Kaplan, IW Chen, N. Gau, J. Fearn, H. Maxon, C. Volle, EA Stein: Evaluation and comparison of radio-, fluorescence, and enzyme-linked immunoassays for serum thyroxine. In: Clin Biochem. 14 (4), Aug 1981, pp. 182-186. PMID 7028316
  11. S. Yong, Y. Chen, TK Lee, HK Lee: Determination of total thyroxine in human serum by hollow fiber liquid-phase microextraction and liquid chromatography-tandem mass spectrometry. In: Talanta. 126, Aug 2014, pp. 163-169. PMID 24881548
  12. SL La'ulu, KJ Rasmussen, YES Straseski: Pediatric Reference Intervals for Free Thyroxine and Free Triiodothyronine by Equilibrium Dialysis Liquid Chromatography Tandem Mass Spectrometry. In: J Clin Res Pediatr Endocrinol. 8 (1), Mar 5, 2016, pp. 26–31. PMID 26758817
  13. YJ Ko, JY Kim, J. Lee, HJ Song, JY Kim, NK Choi, BJ Park: Levothyroxine dose and fracture risk according to the osteoporosis status in elderly women. In: J Prev Med Public Health. 47 (1), Jan 2014, pp. 36-46. PMID 24570805
  14. S. Bhasin, W. Wallace, JB Lawrence, M. Lesch: Sudden death associated with thyroid hormone abuse . In: Am. J. Med. Volume 71 , no. 5 November 1981, pp. 887-890 , PMID 7304660 .
  15. B. Hartung, M. Schott, T. Daldrup, S. Ritz-Timme : Lethal thyroid storm after uncontrolled intake of liothyronine in order to lose weight . In: Int. J. Legal Med. Volume 124 , no. 6 , November 2010, p. 637-640 , doi : 10.1007 / s00414-010-0423-y , PMID 20145940 .
  16. US Food and Drug Administration's Decision Regarding Bioequivalence of Levothyroxine Sodium. In: Thyroid. 14 (7), 2004, pp. 486-486; doi: 10.1089 / 1050725041517138 .
  17. Arne Krehan, Manuela Dittmar, Andre Hoppen, Klaus Lichtwald, George J. Kahaly: Randomized, double-blind crossover study on the bioavailability of levothyroxine. In: Medical Clinic. 97 (9), 2002, pp. 522-527. doi: 10.1007 / s00063-002-1190-4 .
  18. Hans-Ulrich Melchert, Bernd Görsch, Wulf Thierfelder: Thyroid hormones and thyroid medication in test subjects in the national health surveys . Robert Koch Institute, Berlin 2002, ISBN 3-89606-138-0 .
  19. G. Löffler, PE Petridas: Biochemistry and Pathobiochemistry . 9th edition. Springer-Verlag, Berlin 2014, ISBN 978-3-642-17972-3 , pp. 514 .