T3 Liothyronine

What is T3?

T3 is a thyroid hormone, which in its natural form is called triiodothyronine, and the synthetic L-isomer (a slightly modified chemical structure) is called liothyronine.

What is the thyroid gland?

The thyroid is an endocrine gland, located in the neck, surrounding the trachea [Image 1 and Image 2], that produces two hormones, T4 and T3 (being T3 the active form, sooner or later T4 becomes T3), these hormones are necessary to control the body metabolism, there are several diseases that will generate an excessive production (like Graves’ disease) that will lead to weight loss, palpitations, sweating, etc. [1]

Other diseases (like Hashimoto disease) will lead to an under production of hormones which will cause exactly the opposite. [2]

Image 1. Thyroid Gland. Source: Wikipedia (http://en.wikipedia.org/wiki/Thyroid#mediaviewer/File:Thyroid_vector.svg)

Image 2. Thyroid Gland Anatomy. Source: National Cancer Institute. (http://www.cancer.gov/images/cdr/live/CDR719086-750.jpg )

Just like testosterone, T3 and T4 are regulated by a negative feedback, a low T3 or T4 level will stimulate hypothalamus to produce TRH (thyrotropin releasing hormone) which subsequently will go to the pituitary gland and produce TSH (thyroid stimulating hormone) which will then go to the thyroid gland and produce T4 and T3 [Image 3].

Image 3. Thyroid gland negative feedback. Source: BMJ Best Practice. (http://bestpractice.bmj.com/best-practice/monograph/1121.html)

Finally, T4 and T3 are released from the gland, T3 will be instantly active, while T4 will transform in T3 when needed. Therefore is no surprise that synthetic thyroid hormones have been used for decades to lose weight.

When to use it? 

Bodybuilders find it useful in the “cutting” phase, to lose fat and increase muscle definition; increasing metabolism will therefore increase energy demands which will consume glycogen and ultimately, fat.

When using T3 for this purpose the user must be careful not to use doses higher than those recommended (about 25-75mcg per day for no longer than 6 weeks) and must get a thyroid panel (T3, T4 and TSH blood levels), before, during and after using it. [3]

How to use it?

Our way of using it is to start with 25 mcg daily, then increase by 25mcg every 1 week until reaching 75mcg daily, then continue for 2 weeks, and start decreasing it by 25mcg every week, to complete a 6 week cycle.

How is it supplied?

There are 5mcg, 25mcg and 75mcg tablets available in the market, being Cytomel the trademark name in many countries, yet there are many other names like: Dispon (IT); Halotri (ES); Iobolin (BR); Liothyronin (NO, PL, SE); Neo-Tiroimade (PT); T3 (GR, PY); Tertroxin (AU, CZ, GB); Tetronine (KR); Thybon Henning (DE); Thyronine (JP); Thyrotardin inject. (DE); Ti-Tre (IT); Tri-Iodo-Tironina (AR); Trijodthyronin (AT, PL); Trijodthyronin BC (DE); Triyodotironina (ES); Triyotex (CR, DO, GT, HN, MX, PA, SV)

Pharmacodynamics and Pharmacokinetics
Onset of action: ~3 hours
Peak response: 2 to 3 days
Absorption: Oral: Well absorbed (95% in 4 hours)
Half-life elimination: 0.75 days
Excretion: Urine [4]

Bibliography

1-. Medline Plus. Hyperthyroidism.
(http://www.nlm.nih.gov/medlineplus/ency/article/000356.htm )
2-. Medline Plus. Hypothyroidism.
(http://www.nlm.nih.gov/medlineplus/hypothyroidism.html )
3-. William Llewellyn. Anabolics, 10th ed. Molecular Nutrition, 2010.

4-. Lexi-Comp. Liothyronine: Drug information

(http://online.lexi.com/lco/action/home )