Methods and compositions comprising N-acetylcysteine amide (NAC amide) and derivatives thereof are used in treatments and therapies for human and non-human mammalian diseases, disorders, conditions and pathologies. Pharmaceutically or physiologically acceptable compositions of NAC amide or derivatives thereof are administered alone, or in combination with other suitable agents, to reduce, prevent, or counteract oxidative stress and free radical oxidant formation and overproduction in cells and tissues, as well as to provide a new source of glutathione.