For example, NAC mainly increases glutathione, the primary antioxidant your body uses, so it may reduce the level of oxidative stress and lower your body's stress response. It also increases the level of SAM-e in your body (as you can transform sulfur containing amino acids methionine and cysteine into each other). SAM-e is a crucial cofactor for many processes including creation of neurotransmitters such as dopamine and serotonin. And an increase in sulfur amino acids (including NAC) also modulates your gut microbiome.