I used to see girls at Gold's all the time back in the early '90s who fell in love with thyroid meds... and then they stayed on them to long. They looked like bloated cows when the finally went off.
my wife has done it over a half dozen times with no problems but the longest she stays on is 4 weeks at no more than 75mcg she cycles it up slow and down slow 5 days 25 5days 50 10 days 75 then back down 5 50 and 5 25.