我百毒不侵但曾无可救药
[wŏ băi dú bù qīn dàn céng wú kĕ jiù yào]
Conveys that while now resilient against many things ('immune to all toxins'), there was a time when one felt irrevocably troubled or affected ('once beyond cure'). It speaks to having found inner strength after overcoming personal turmoil.