I had Graves, then RAI in 1990, then hypo and on Levo, mostly 175mcg. Something changed in 2014, and I became very very ill. T4 at top of range, T3 at the bottom. I started T3 in 2016, and wow my life came back. Does anyone know how much RAI affects T4 to T3 conversion? The Endo told me at the time of my RAI that it would only destroy some of my thyroid, but they'd err on the side of making me hypo instead, as that's easy to treat...Yes, right!! So I don't know how much was destroyed. I was relatively ok on 175 Levo for 24 years; them wham, immense weakness etc etc - all the hypo symptoms. So what would provoke the change after 24 years? Does RAI ultimately affect conversion?