The physicians I talk to argue that only these synthetic preparations of T4 provide steady hormone levels. Three decades of testing hypothyroid patients have taught me that most people can't convert T4 to the more active form, T3, which is done mainly in the liver. This is easy to confirm by measuring the active/free hormone levels, but this rarely happens.
The natural alternative is to use a preparation that contains the full range of thyroid hormones in the ratio of T3 to T4 that the normal-thyroid patient has. An herb called guggal supports the liver's conversion of T4 to T3, but this often isn't effective enough. Then I use the natural alternative if possible: names include Armour, Nature-Throid, Westthroid, et. al.
Another supplementation option is to give T3 (brand name Cytomel) along with one of the T4-only synthetic preparations. Careful monitoring must follow this because T3 is approximately 9 times more powerful than T4 and performs a lot more of the work of thyroid hormone in the body. Too much T3 (or even too much T4) can easily overstimulate people, causing the following symptoms of excess thyroid hormone:
1. heart palpitations
2. nervousness/difficulty relaxing
3. fine tremor
4. feeling hot and sweaty
5. clammy skin
6. possible weight loss
Excess thyroid can contribute to early bone density loss over a long period of time.
Most patients need to be evaluated every 4 to 6 weeks until they reach a plateau of normalcy. For most patients, the lab test results correlate fairly well with how they feel. Those patients whose test results do not represent how they feel seem to be on the increase, and they require more careful evaluation, "outside the box," so to speak.
Finally, how and when to dose these hormones is more than I want to explain here. However, there is one common mistake that I see in many patients' dosing schedule. Having calcium and iron supplements in the stomach when swallowing thyroid hormones of any type seems to significantly inhibit absorption of the hormone. These minerals should be taken preferably at least 2 to 3 hours after the hormone is swallowed.