Description

Drug Class: Synthetic thyroid hormone. (ORAL)

Average Reported Dosage: 25-150 MCG daily.

Noted Comments: Significant suppression of Thyroid function during use

Cytomel is the synthetic form of T-3/L-triiodothyronine and was a commonly known trade or brand name among athletes. T-3/L-triiodothyronine is used as a form of thyroid hormone therapy mostly in Europe. Most bodybuilders favored this drug over synthetic forms of T-4/L-thyroxine due to its vastly superior activity level.

An advantage of T-3/L-triiodothyronine administration over T-4/L-thyroxine was the lack of dependence upon the liver enzyme responsible for T-4/T-3 conversion. During diet restricted periods the liver naturally decreases the liver enzyme levels as a control measure to prevent metabolic rate induced starvation. Just as the liver increases production of this enzyme in response to elevated calorie intake it also reduces levels in response to decreased calorie intake. Remember that T-4 /L-thyroxine is only 20% as active as T-3/L-triiodothyronine.

The abuse of synthetic T-3/L-triiodothyronine will result in severe suppression of natural (endogenous) thyroid function. This is especially true of this drug because it actually circumvents the normal thyroid hormone manufacturing process the body utilizes to produce endogenous forms as required. Simplified this is because T-3/L-triiodothyronine is the most potent thyroid hormone so the body shuts down each level required for production to try to reduce circulatory T-3/L-triiodothyronine levels. Of course this does not reduce the level if the hormone is being administered exogenously (from outside the body).

Since long term use of T-3 /L-triiodothyronine will lead to thyroid function suppression the issue of rebound should be briefly discussed. It is commonly stated that synthetic thyroid hormone abuse will lead to permanent thyroid gland dysfunction. Though it is definitely a physiological possibility, I have not yet found a case study to support this statement. However, there is a common occurrence of thyroid gland/function rebound in natural endogenous thyroid hormone production. It seems that it was common for individuals to realize an “increase” in endogenous thyroid hormone production of 120-130 % within 3-15 days after drug discontinuance. This means an individual would commonly see an increase in their thyroid hormone production of 20­30% above their normal pre-drug administration levels, in many cases.

The noted positive physiological effects of reasonable dosages of thyroid hormones included:

*Increased protein synthesis rate. *Increased rate of fat oxidation.

*Increased sensitivity of receptors for androgens, Insulin, GH, IGF-1, PGE-1, PGF-2, Clenbuterol, Ephedrine, Creatine, and others.

*Increased metabolization of proteins, carbohydrates, fats and micronutrients. *Increased metabolic rate and calories expenditure. *Enhanced oxygen consumption by most body tissues *Improved recovery time.

The noted negative physiological effects of excessive dosages of thyroid hormones included:

*Loss of lean mass tissue.

*Increased heart rate and palpitations.

*Insomnia.

*Diarrhea.

*Vomiting.

Thyroid hormone drugs are natural or synthetic preparations containing tetraiodothyronine (T4, levothyroxine) sodium or triiodothyronine (T3, liothyronine) sodium or both. T4 and T3 are produced in the human thyroid gland by the iodination and coupling of the amino acid tyrosine T4 contains four iodine atoms and is formed by the coupling of two molecules of diiodotyrosine (DIT). T3 contains three atoms of iodine and is formed by the coupling of one molecule of DIT with one molecule of monoiodotyrosine (MIT). Both hormones are stored in the thyroid colloid as thyroglobulin.

Thyroid hormone preparations belong to two categories (1) natural hormonal preparations derived from animal thyroid, and (2) synthetic preparations. Natural preparations include desiccated thyroid and thyroglobulin. Desiccated thyroid is derived from domesticated animals that are used for food by man (either beef or hog thyroid) and thyroglobulin is derived from thyroid glands of the hog. The United States Pharmacopeia (USP) has standardized the total iodine content of natural preparations. Thyroid USP contains not less than (NLT) 0.17 percent and not more than (NMT) 0.23 percent iodine, and thyroglobulin contains not less than (NLT) 0.7 percent of organically bound iodine. Iodine content is only an indirect indicator of true hormonal biologic activity.