The thyroid gland produces two hormones called triiodothyronine (T3) and thyroxine (T4). They are responsible for metabolic processes such as regulating weight, temperature, heart rate, growth, development, etc. Both of these hormones are produced from a combination of iodine and the amino acid tyrosine.

Levothyroxine and liothyronine are synthetic versions of T4 and T3, respectively. In this article, we will summarise both of them, how they function, their effects, and where you can purchase them.


Levothyroxine is a synthetic version of thyroxine (T4), one of the body’s natural thyroid hormones. It is administered when the body is deficient in thyroxine.

It was useful in treating severe hypothyroidism or myxedema coma in animal test subjects. It demonstrated beneficial effects in euthyroid goiters and thyroid cancer in animals that had undergone thyroidectomy. It also served as an adjunct to surgery and radioiodine therapy.


T4 binds to the thyroid receptor protein in the nucleus. It is converted to its active metabolite, L-triiodothyronine (T3), and controls DNA transcription and protein synthesis. Levothyroxine is a chiral compound in the L-form.

According to research in animal test subjects, T4 is absorbed from the gastrointestinal tract. Its absorption is increased by fasting and decreased in certain malabsorption syndromes, by certain foods, and age.


Liothyronine is a synthetic form of the naturally occurring thyroid hormone, triiodothyronine (T3). It binds to nuclear thyroid receptors and induces gene expression that is necessary for growth and development. Liothyronine is more potent than levothyroxine.


Liothyronine replaces endogenous thyroid hormone and exerts its physiologic effects by controlling DNA transcription and protein synthesis. This effect occurs when it binds to the thyroid receptors attached to the DNA. Therefore, it increases energy expenditure, stimulates growth, maturation, and metabolism of the body tissues. It also aids in myelination of nerves and the development of synaptic processes in the nervous system and enhances carbohydrate and protein metabolism.


Levothyroxine is a synthetic version of T4, and liothyronine is a synthetic version of T3. Both are used for the treatment of hypothyroidism. However, animal test studies show that levothyroxine is preferred because liothyronine is absorbed from the intestine very rapidly, and this may cause mild thyroid hormone toxicity (hyperthyroidism).

T4 is slowly eliminated through its major metabolic pathway to T3 through sequential deiodination, where approximately 80% of circulating T3 is derived from peripheral T4. The liver breaks down both T4 and T3. And they are excreted by the kidneys. A portion of the conjugated hormone reaches the colon unchanged and is eliminated in the feces.

Levothyroxine has a half-life of 6-7 days, while that of liothyronine is between 1-2 days.


You can purchase either levothyroxine and liothyronine from Loti Labs. Buy research liquids that are USA-made for the integrity of your research.


  1. Elio Roti, Roberta Minelli, Eliana Gardini, Lewis E. Braverman, The Use and Misuse of Thyroid Hormone, Endocrine Reviews, Volume 14, Issue 4, 1 August 1993, Pages 401–423, https://doi.org/10.1210/edrv-14-4-401
  1. Eghtedari B, Correa R. Levothyroxine. [Updated 2020 Feb 11]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2020 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK539808/
  2. Colucci P, Yue CS, Ducharme M, Benvenga S. A Review of the Pharmacokinetics of Levothyroxine for the Treatment of Hypothyroidism. Eur Endocrinol. 2013;9(1):40–47. doi:10.17925/EE.2013.09.01.40
  1. Leese GP, Soto-Pedre E, Donnelly LA. Liothyronine use in a 17 year observational population-based study – the tears study. Clin Endocrinol (Oxf). 2016;85(6):918–925. doi:10.1111/cen.13052
  1. CLARK T. SAWIN, JEROME M. HERSHMAN, INDER J. CHOPRA, The Comparative Effect of T4 and T3 on the TSH Response to TRH in Young Adult Men, The Journal of Clinical Endocrinology & Metabolism, Volume 44, Issue 2, 1 February 1977, Pages 273–278, https://doi.org/10.1210/jcem-44-2-273

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