The International Hormone Society’s Consensus Group of experts on Hormone Therapies Consensus nr 1 on “Thyroid Hormone Therapy of Hypothyroidism”of the 29-9-2005

After having reviewed the scientific literature and exchanged experiences between physicians from all over the world and who are competent in hormone therapies, we, members of the Consensus Group of Experts of the International Hormone Society, think the time is ripe to reconsider current concepts on thyroid treatment of hypothyroidism.

The view that hypothyroidism is best treated by thyroxin alone is not based on solid scientific evidence. The studies with comparison of the efficacy of thyroxine alone versus that of associations of thyroxine and triiodothyronine medications have in general not shown superiority of thyroxine alone above the associations of thyroxine with a smaller dose of triiodothyronine. On the contrary, a few studies have shown significantly greater efficacy of combined thyroxine-triiodothyronine medications compared to the use of thyroxine alone in humans on such divergent parameters as serum cholesterol, mental and physical symptoms, and in animals on goitre formation and intracellular triiodothyronine(T3)-euthyroidism, just to name some of the greater benefits. The fact that T3 is the major intracellular thyroid hormone, that it is the low serum level of T3 that forms, more often than serum T4 (thyroxin) or TSH, the critical parameter in mortality studies, especially cardiovascular, and that the absorption of T3 is much more efficient and stable than that of T4, give credit to the view that associations of thyroxin with triiodothyronine may better fit the hypothyroid patient.

The evidence is sufficient to guarantee the physician a freedom of choice in thyroid medication: either thyroxin alone, either thyroxin and triiodothyronine.

As hypothyroidism has serious adverse consequences on the quality of life and health of patients, we recommend physicians at the light of the solid evidence here collected, to first try with hypothyroid patients a combined thyroxin and triiodothyronine preparation.

As the association treatment contains the immediately active triiodothyronine, we recommend physicians to follow some safety guidelines, next to the classical ones such as avoiding overdoses, when they administer thyroxin and triiodothyronine medications. Following these measures increases the safety and tolerance of the treatment. The first guideline is to start the treatment at very low doses and then to slowly and gradually increase the dose until clinical euthyroidism is reached. The second guideline is to tell their patient to avoid all caffeinated and similar stimulating drinks that may increase the orthosympathic activity. The third guideline is to regularly follow-up the patients with a good clinical interview and examination and laboratory tests every two to twelve months depending on the patient’s needs. The forth guideline is to carefully screen for adrenal deficiency in hypothyroid patients as patients with low or borderline low cortisol levels may poorly tolerate any type of thyroid medication, and in particular thyroxin-triiodothyronine combinations. The intolerance may come from overactivity of the orthosympathic nervous system that often accompanies states of low cortisol, and an excessive and rapid conversion of thyroxin to triiodothyronine that puts these patients easily into a state of excess T3 and thus hyperthyroidism, and further increases the orthosympathic activity. In patients with cortisol deficiency, we recommend the physician to treat the low cortisol state prior or concomitantly to the thyroid treatment. If not, thyroxin alone may be the better treatment of hypothyroidism in the presence of an untreated cortisol deficiency. In most other states, thyroxin and triiodothyronine remains the first, but not exclusive, choice for treatment of hypothyroidism for the International Hormone Society’s consensus group.

Concerning the debate about which association treatment works best: synthetic T3-T4 or dessicated thyroid, the consensus group states the following. Reports of patients feeling better on dessicated thyroid may have scientific evidence as these preparations contain next to T3 and T4 also a number of other substances that may have some thyroid activity as diiodo-and monoiodo-thyronines. In addition, the binding of much of the thyroid homones to the bigger thyroglobulin molecule permits a slower intestinal absorption and, later, once arrived in the bloodstream, a slower release of thyroid hormones in the blood, thereby insuring a more persistent action and a better tolerance by spreading the action over a longer time. Thus, dessicated thyroid may work better. The view that the potency of thyroid preparations of animal origin may have more fluctuations has arguments. For this reason, preference is given to preparations that are officially registered and well-controlled. It must be said that the frequent FDA-recalls of poorly reliable, less potent than announced thyroxin preparations of various pharmaceutical firms in the USA, makes thyroxin not a better alternative. In the light of the Mad Cow’s disease, the International Hormone Society does not recommend the use of dessicated thyroid of beef origin. For these reasons, the position adopted by the consensus group members of The In,ternational hormone society is that both type of T3 -T4 preparations have their pros and cons, and the freedom of choice between these two should be left over to the physician.