I personally wouldn't use it for an extended period.
Last thing you need is TSH shut down.
Some sources around here carry the 50mcg tabs, nice small ones (for reference, I run 150 mcg of Synthroid per day..t4).. FYI, I have Hypothyroidism.. so dont run that high... just a benchmark of what someone with a totally FUCKED Thyroid has to run.
That protocols gets me to the same level as a healthy person.
When it's time to cut, ill toss in another 25mcg of T3 AND T4 with my HgH regiment (some excellent studies showing GH impact on Thyroxin production being suppressed during GH injections)
I will sometimes run 50mcg each extra, for extended periods of time... because honestly, I dont give a shit if my production gets shut down lol.