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Structural formula
Structural formula of L-triiodothyronine
Non-proprietary name Liothyronine
other names
  • 3,3 ', 5-triiodo- L- thyronine
  • O - (4-Hydroxy-3-iodophenyl) -3,5-diiodo- L -tyrosine
  • ( S ) -2-Amino-3- [4- (4-hydroxy-3-iodophenoxy) -3,5-diiodophenyl] propanoic acid
Molecular formula C 15 H 12 I 3 NO 4
External identifiers / databases
CAS number 6893-02-3
EC number 229-999-3
ECHA InfoCard 100.027.272
PubChem 5920
ChemSpider 5707
DrugBank DB00279
Wikidata Q327362
Drug information
ATC code

H03 AA02

Molar mass 650.97 g · mol -1
Physical state


Melting point

234-238 ° C


practically insoluble in water (3.96 mg / l at 37 ° 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
07 - Warning


H and P phrases H: 315-319-335
P: 261-305 + 351 + 338
As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions .

Triiodothyronine or triiodothyronine ( T 3 , also fT 3 for free triiodothyronine and rT 3 for reverse triiodothyronine ), also liothyronine ( INN ), is one of two important thyroid hormones . It is the most effective hormone of the thyroid gland and its biological activity exceeds the second iodine- containing thyroid hormone tetraiodothyronine (T 4 ), also called thyroxine or levothyroxine, three to five times, according to other data by a hundred times.

The two iodine-containing thyroid hormones only differ in the number of bound iodine atoms, namely three for triiodothyronine and four for thyroxine - hence the abbreviations T 3 and T 4 . If triiodothyronine is not bound to proteins in the blood , it is referred to as free triiodothyronine (fT 3 ) . The isomer , in which there is only one iodine atom on the inner benzene ring and two iodine atoms on the outer ring, is known as reverse triiodothyronine (rT 3 ) - it is a breakdown product of thyroxine and a biologically inactive form of triiodothyronine.

Triiodothyronine is chiral . The natural product is L- triiodothyronine [synonym: ( S ) -triiodothyronine]. If “triiodothyronine” is listed in the following text and in the scientific literature without any additional name ( prefix ), L- triiodothyronine is always meant.

The identification of triiodothyronine by chemical isolation and synthesis was first carried out in 1951 by Jack Gross (1921–1994) and Rosalind V. Pitt-Rivers (1907–1990).


The T 3 molecule contains 58.5% by mass of iodine .

T 3 only makes up 5 to 10% of the two thyroid hormones and has a half-life ( half-life ) of around 10–19 hours in the human body, so it is quickly broken down again. This is only possible because of T 4 with the help of deiodinases ( Engl. Deiodinase) is formed if necessary. Deiodases 1 and 2 (DIO1 and DIO2) remove an iodine atom from the 5 'carbon and convert the less active T 4 into active T 3 .

T 3 and T 4 are about 99.95% in bound form, and only about 0.05% are also in free form. The free form of the T 3 hormone is metabolically active.

Ratio T 3 to rT 3

The ratio of T 3 to rT 3 changes in states of exhaustion and very serious illnesses. In these cases the ratio of rT 3 to T 3 increases . It is assumed that the purpose is to free energy resources for the vital processes. Other thyroid hormones also show reactive changes. The ratio of thyroid hormones can thus be used to assess the prognosis of patients in the clinic.

Therapeutic use

Triiodothyronine is occasionally given to treat an underactive thyroid ( hypothyroidism ). Usually a combination with thyroxine is then used. The physiological effects are largely identical, but a study found a stronger positive effect on mood.

Side effects

As unwanted side effects may occur: heart failure , atrial fibrillation , muscle weakness , bone loss , hair loss , mental changes, nervousness as well as fatigue , loss of libido and impaired sexual function in women oligo- or amenorrhea , in men (rare) gynecomastia , etc. T 3 is for losing weight not permitted, especially since other methods are available.

Triiodothyronine abuse

In the bodybuilder scene , T 3 is to be touted for "rapid fat loss ". It causes symptoms in healthy people that correspond to hyperthyroidism (and are known as thyrotoxicosis factitia ) and also lead to weight loss by accelerating fat breakdown and metabolism . As a result, the user not only loses fat, but also a considerable amount of muscle mass . Some also claim that appetite is reduced, but the opposite is the case.

Trade names

Thybon (D)

Combination preparations
with thyroxine : Novothyral (A, CH, D), Prothyrid (D)

In Austria, the production and sale of triiodothyronine and Combithyrex was discontinued in mid-2016, which means that there is no single preparation and only a single combination preparation available in Austria.

Related links

Individual evidence

  1. a b c data sheet 3,3 ′, 5-Triiodo-L-thyronine from Sigma-Aldrich , accessed on April 24, 2011 ( PDF ).
  2. Entry on triiodothyronine in the ChemIDplus database of the United States National Library of Medicine (NLM) .
  3. ^ Frank Grünwald and Karl-Michael Derwahl: Diagnosis and Therapy of Thyroid Diseases, Frankfurt, Berlin, 2014, ISBN 978-3-86541-538-7 , p. 15.
  4. ^ Hans-Christian Pape, Armin Kurtz, Stefan Silbernagl: Physiology . 7th edition. Georg Thieme Verlag, Stuttgart 2014, ISBN 978-3-13-796007-2 , p. 620 .
  5. ^ A b Hans-Christian Pape, Armin Kurtz, Stefan Silbernagl: Physiology . 7th edition. Georg Thieme Verlag, Stuttgart 2014, ISBN 978-3-13-796007-2 , p. 622 .
  6. J. Gross, R. Pitt-Rivers: II. Thyroid hormone physiology and biochemistry. Triiodothyronine in relation to thyroid physiology. In: Recent Progress in Hormone Research. Volume 10, 1954, p. 109.
  7. Alischa Quindeau: Cooperation and competition in endocrinological research using the example of the identification of thyroid hormones. Medical dissertation, Heinrich Heine University Düsseldorf 2019, p. 2 f.
  8. Milestones in European Thyroidology (MET): Rosalind Venetia Pitt-Rivers (1907-1990).
  9. G. Löffler, PE Petrides: Biochemistry and Pathobiochemistry. Springer, Berlin 2006.
  10. Deutsches Ärzteblatt: Hypothyroidism: Substitution with T4 and T3?
  11. Janet S. Kinney et al. a .: Community outbreak of thyrotoxicosis: Epidemiology, immunogenetic characteristics, and long-term outcome. In: The American Journal of Medicine. Volume 84, No. 1, January 1988, pp. 10-18, PMID 3257352 .
  12. Mailing of the pharmaceutical company substitute for triiodothyronine and Combithyrex (PDF)