Hello, I'm on t3 only since Xmas 2015. 40 mcg daily feeling well. However my question is can high dose and prolonged use of T3 cause organ damage. I'm worried as I've just been told this by a thyroid pharmacist. I'm not on a high dose and only been on it few months, but I'd never heard of this and I feel so well on t3 alone in comparison to ndt. But wonder is something nasty in store for me using it alone. As she said t4 is important for the body. For whatever reason I don't get on too great with t4. Well thought I'd ask you guys. Thanks a lot now.