I've read that it can take 6-12 months to find the optimal dose.
I just started taking levothyroxine (generic synthroid) in March '10....at my request, my doctor has checked my blood levels every 4-6 wks.
I'm not too crazy about how long it takes for symptoms to dissipate so, my goal is to keep my levels at my setpoints rather than wait for symptoms to tell me I need a dose adjustment.
It took awhile to find my setpoints (MY normal FT4/FT3 levels within the ranges of normal) and now I'm finally able to adjust my dose to keep them there.
Of course, my body could decide it still wants to mess me up but this is my plan for now