Both. They both work differently, but if I had to chose one it would be NAC, because it supports many healthy functions of the body. It not only protects renal and hepatic function, but it also chelates heavy metals. It aids in production of glutathione, which is a strong anti oxidant, which supports many of the body's vital functions. It supports the immune system, and transports nutrients to lymphocytes (immune cells), and helps rid the body of toxic material and free radicals. One thing about it is, you should stack some extra vitamin c when using this, because it can also deplete your body of this essential antioxidant.