Levothyroxine (INN, USAN) or L-thyroxine is a synthetic thyroid hormone that is chemically identical to thyroxine (T4), which is naturally secreted by the follicular cells of the thyroid gland. It is used to treat thyroid hormone deficiency, and occasionally to prevent the recurrence of thyroid cancer.
Like its naturally secreted counterpart, levothyroxine is a chiral compound in the L-form. The related drug dextrothyroxine (D-thyroxine) was used in the past as a treatment for hypercholesterolemia (elevated cholesterol levels) but
was withdrawn due to cardiac side effects. It is on the World Health Organization’s List of Essential Medicines, a list of the most important medication needed in a basic health system.
T4/L-Thyroxine is pro-hormone, which your body converts into T3 at necessary rate only and thus it could be considered as much milder and safer drug than T3.
L-Thyroxine is an excellent fat burner since your metabolism is greatly increased while being on it. You can afford to be a little sloppier on pre-contest dieting since it will still burn fat when you are taking in a lot of calories since your metabolism is going haywire.
L-Thyroxine is widely used by bodybuilders and fitness addicts on pre-competition cycle in order to get relief, also used by overweighed people to reduce weight. It increases metabolism and produces general stimulating effects. However, this substance should be used wisely.
COA
| Product name |
L-Thyroxine |
| Appearance |
White crystalline powder |
| Assay(*) |
98~101.0% |
99.3% |
| Identification |
By UV, To match with working standard |
Complies |
| Related Substances |
Not more than the reference solution (0.05%) |
Complies |
| Heavy metals |
≤10ppm |
10ppm |
| Loss on drying |
<0.5% |
0.15% |
| Resiue on ignition |
≤0.1% |
0.05% |
| Melting |
235°C |
Complies |
Precautions of T4
Thyroid medication is frequently used by bodybuilders who are getting ready for a contest, and really, I can’t remember seeing a bodybuilder dieting for any major show in the last decade who hasn’t told me that they use Thyroid medication. Most of the time, T4 is only used when T3 can not be found.
Recently though, due mostly to an article written by myself and Dr.James Daemon, T4 has been experiencing a bit of a renaissance. This is due to it being a bit more muscle sparing, and synergy with growth hormone. Most bodybuilders use use GH for precontest dieting, and T4 has found a bit of a niche for those using GH and dieting. At this point, whether on a diet or not, T4 has become a much sought after drug for use with cutting cycles which include Growth hormone. I have even received a phone call from doctors and Hormone Replacement Clinics, who wanted more practical information on the use of GH + T4.
So, at this point, I think that most of the people in the bodybuilding world who are using T4 are using it along with their Growth Hormone for the most part.
Anecdotally, many bodybuilders feel that T4 is less harsh on muscle tissue and they’re able to maintain more muscle when dieting down by using T4, than compared with when they’ve used T3.
Usage and Dosage
Users discovered T3 to be a better choice over T4 when using Thyroid drugs during Cyclic Ketogenic Diets.
One of the thyroid hormones involved in the maintenance of metabolic homeostasis. Synthesized and stored as amino acid residues of thyroglobulin, the major protein component of the thyroid follicular colloid. Synthesis and secretion are regulated by the pituitary hormone (TSH).
Levothyroxine is a synthetic (man-made) version of the principle thyroid hormone, thyroxine (T4) that is made and released by the thyroid gland. Thyroid hormone increases the metabolic rate of cells of all tissues in the body. In the fetus and newborn, thyroid hormone is important for the growth and development of all tissues including bones and the brain. In adults, thyroid hormone helps to maintain brain function, food metabolism, and body temperature, among other effects
Liothyronine Sodium is a synthetic variant of the human body’s own thyroid hormone. Indicated as a sympathicolytic and mydriatic. It may have activity as an aphrodisiac. It is suitable for various causes of hypothyroidism.
T4 must be used in much higher doses to be as effective as T3. Subjects found they needed to use a dosage of 300 mcg/day to achieve the same results as 25-100 mcg/day of T3 (Cytomel).
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