I wonder how those who make the Guidelines and who withdrew T3 in the UK to those who desperatey needed it to be well, will promote this day?
Three excerpts for ATA and I believe the BTA follow these guidelines too.
Desiccated (dried and powdered) animal thyroid (Armour®), now mainly obtained from pigs, was the most common form of thyroid therapy before the individual active thyroid hormones were discovered. People can still buy it over the Internet—legally if it’s sold as a food supplement, but illegally if it’s sold as a medicine. It is also available still as a prescription. Since pills made from animal thyroid are not purified, they contain hormones and proteins that never exist in the body outside of the thyroid gland. While desiccated thyroid contains both T4 and T3, the balance of T4 and T3 in animals is not the same as in humans, so the hormones in animal thyroid pills aren’t necessarily “natural” for the human body. Further, the amounts of both T4 and T3 can vary in every batch of desiccated thyroid, making it harder to keep blood levels right. Finally, even desiccated thyroid pills have chemicals (binders) in them to hold the pill together, so they are not completely “natural”. Desiccated animal thyroid is rarely prescribed today, and there is no evidence that desiccated thyroid has any advantage over synthetic T4.
While most actions of thyroid hormone are most likely due to T3, most T3 in the body comes from the conversion of T4. The conversion of T4 to T3 is normal in hypothyroid patients. T3 has a very short life span in the body, while the life span of T4 is much longer, ensuring a steady supply of T3. A preparation of synthetic T3 (Cytomel®) is available. After taking a tablet of Cytomel® there are very high levels of T3 for a short time, and then the levels fall off very rapidly. This means that T3 has to be taken several times each day, and even doing this does not smooth out the T3 levels properly. In addition, it is impossible to avoid having too much thyroid hormone in the system soon after each dose of T3 is taken. High T3 levels can lead to unpleasant symptoms such as rapid heart beat, insomnia and anxiety. High T3 levels also can harm the heart and the bones. Another concern with using T3 treatment is that the body is deprived of the ability to adjust the conversion of T4 to T3 to regulate the supply of T3 according to the body’s own needs. Thus, there is no indication for the use of T3 alone for the treatment of hypothyroidism.
(this isn't strictly true as I had worse palps on levo alone and take T3 once daily)
Some hormone preparations containing both T4 and T3 are available in the United States (Thyrolar®). Combination T4/T3 preparations contain much more T3 than is usually produced naturally within the body. Because of this, they can have the same side effects as T3 given by itself. It is also given once a day, ignoring the short life span of T3 in the body. There has been interest in whether a combination of T4 and T3, with a lower amount of T3 given more than once a day, might result in better treatment of hypothyroidism, especially in those patients that do not feel completely normal on T4 alone. In these cases, Cytomel® (T3) is taken in addition to T4. A trial period of 3 – 6 months is reasonable to determine if combination T4 and T3 therapy will help.