The replacement hormone starts to work immediately. The medication you are on is T4 which has a half-life in the body of just a tad under seven days. So any that is not used one day, is still around available for use for another day (or more). The dose you are on will accumulate, in other words. T4 is converted in many parts of the body into T3 as we need it (T3 is the form the cells need for metabolic purposes). You will need additional blood tests to determine whether or not the dose the doctor has you on is the correct dose for you. (For this test, you need to wait — we wait for the dose to accumulate properly, and then we wait a bit longer for the pituitary’s TSH levels to adjust to the dose). Even if the dose you are on turns out the be the correct dose for you, it takes time for the swelling to be reabsorbed, and any inflammation in joints or muscle tissue to subside. It would be nice if it all happened quickly, but it doesn’t, so you need to be tuned into “progress” rather than “normal” right now.
As for your RAI working “too well,” I think that perhaps you should think in terms of “hurrah, it’s gone!” I realize it’s a pain to have to deal with severe hypo right now, but the better the RAI works, the less likely it is that you will have to deal with major fluctuations of thyroid activity in the future. The antibodies are still there: if there is sufficient thyroid tissue left after RAI or surgery, those antibodies CAN make you ill again. I have several friends who have had thyroid cancer, and they have had surgery AND huge doses of RAI to eliminate every last vestige of thyroid tissue in their bodies. They are active, healthy people on replacement hormone. The replacement hormone does work to keep us healthy. So, even if your RAI took out all of your thyroid tissue, you can expect to live a healthy, full and active life — all other things being normal.
I hope you are seeing progress, and feeling much better soon.
Bobbi — NGDF Online Facilitator