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Chemical Name: Liothyrine Sodium Drug Class: Thyroid Agent
Cytomel is the most common brand name for a synthetic thyroid hormone- more specifically, it’s a synthetic version of T3 (triiodothyronine ). T3 is not produced directly by your thyroid gland, is actually converted from the T4 thyroid hormone (thyroxine). (1)
T3 functions as the more metabolically active of two primary thyroid hormones, and is a regulator of oxidative metabolism of energy producing substrates by your cell’s mitochondria. The mitochondria produce ATP, which is used by the body as energy, and since T3 supplementation causes an increase in ATP, by using Cytomel, you will increase overall metabolic activity(1)(2). It does this in part by increasing your cardiac output (Which will puts demands on your ATP usage, and this increased heart rate and increased force of contraction of the cardiac muscle accounts for 30-40% of ATP usage in abnormally elevated thyroid levels (3).T3 also may cause the body to increase its production of uncoupling proteins. Uncoupling proteins are a transporter family present in the mitochondrial inner membrane. It serves to uncouple respiration from ATP synthesis by dissipating (uncoupling) the transmembrane proton gradient as heat. This makes the body highly inefficient at producing useful energy, because in lieu of ATP being produced from energy substrates, heat is generated instead, without providing the body with useful energy. As you may suspect, this means you are burning calories without actually producing useful energy- i.e. you burn calories just sitting around. Then when you actually need to produce energy from foodstuffs, you have already burned off a fair portion which was released as useless heat. This uncoupling likely occurs in skeletal muscle, and this is one mechanism by which T3 (Cytomel) can cause an increase in basal metabolic rate(4).
This increase in overall metabolic activity has many additional benefits. Cytomel will enhance your body’s ability to synthesize protein. This could actually result in an increase in muscle mass, although fat-burning is the primary effect athletes are seeking with Cytomel usage. Not too many people report this, however, although at low doses it does seem to provide at least a little benefit in this department. Overdosing can result in a decrease in muscle mass, however- but when used concurrently with steroids, this is unlikely. When you’re seriously dieting, additional Cytomel is a good idea if the scale isn’t moving for a week or so.
Additionally, in all of the studies I’ve seen, T3 also increased growth hormone (GH) production. (5)(6) and since GH is also a strongly lipolytic compound, this transcriptional increase may be yet another mechanism of action by which T3 exerts its effects. Unfortunately, it has been noted by me elsewhere that T3 when used concurrently with GH causes a decrease in the nitrogen retention normally found with GH(7). The solution, which has been covered extensively by me elsewhere
Another interesting benefit of having some extra T3 floating around your body is that T3 has been shown to possibly (probably) upregulate the beta 2 receptors in adipose tissue. This makes it a very potent and synergistic stack with both Clenbuterol as well as Albuterol or even ephedrine.
I’ve always been an advocate of stopping Cytomel use immediately and without tapering, when you are finished with using it. Numerous studies I’ve read at have shown people recovering their thyroid hormone relatively quickly (within months, at most) after going off of years of thyroid replacement therapy (9)(10)- recovering, in fact, as quickly as people who have only been on it for a few weeks. Supplementing your thyroid recovery after you go off Cytomel with Clomid & HCG, as well as some sort of a green tea product (forskolli), a guggulsterone product, and some Tyrosine is a good idea.
Cytomel remains easy to find on the black market and is relatively cheap.
1. Human Anatomy and Physiology, 6th Edition. John w. Hole jr.
2. Physicians Desk Reference
3. Annu Rev Nutr 1995;15:263-91 Thermogenesis and thyroid function. Freake HC, Oppenheimer JH.
4. J Clin Invest 2001 Sep;108(5):733-7 Effect of triiodothyronine on mitochondrial energy coupling in human skeletal muscle. Lebon V, Dufour S, Petersen KF, Ren J, Jucker BM, Slezak LA, Cline GW, Rothman DL, Shulman GI.
5. Role of thyroid hormone in the control of growth hormone gene expression Braz J Med Biol Res 1994 May;27(5):1269-72. Volpato CB, Nunes MT.
6. Low-dose T(3) improves the bed rest model of simulated weightlessness in men and women. Am J Physiol 1999 Aug;277(2 Pt 1):E370-9 Lovejoy JC, Smith SR, Zachwieja JJ, Bray GA, Windhauser MM, Wickersham PJ, Veldhuis JD, Tulley R, de la Bretonne JA.
7. Effects of long-term growth hormone (GH) and triiodothyronine (T3) administration on functional hepatic nitrogen clearance in normal man. Wolthers T, Grofte T, Moller N, Vilstrup H, Jorgensen. J Hepatol 1996 Mar;24(3):313-9
8. Alpha 2- and beta-adrenergic receptor binding and action in gluteal adipocytes from patients with hypothyroidism and hyperthyroidism Metabolism 1987 Nov;36(11):1031-9 Richelsen B, Sorensen NS
9. Recovery of pituitary thyrotropic function after withdrawal of prolonged thyroid-suppression therapy. N Engl J Med 1975 Oct 2;293(14):681-4 Vagenakis AG, Braverman LE, Azizi F, Portinay GI, Ingbar SH.
10. Patterns off recovery of the hypothalamic-pituitary-thyroid axis in patients taken of chronic thyroid therapy. J Clin Endocrinol Metab 1975 Jul;41(1):70-80 Krugman LG, Hershman JM, Chopra IJ, Levine GA, Pekary E, Geffner DL, Chua Teco GN