Lots of people on this site are told that subnormal TSH is bad for you on thyroid therapy. My wife has had a totally destroyed thyroid for 46 years. She's on T4 only (125,150 alternately) and has never had a detectable TSH in all that time. No osteoporosis, v occasional AF. Last blood test this month gave TSH 0.06, FT4 16.7. TSH subnormal, FT4 in the middle of the range. At 76 she is doing well for her age. Just a note to say that lifelong suppressed TSH needn't be a problem, short term or long.