What Is N-Acetyl L-Cysteine N-Acetyl L-Cysteine, also called acetylcysteine, is derived from the amino acid, L-Cysteine, and is a source of Cysteine for the body. N-Acetyl L-Cysteine Benefits N-Acetyl L-Cysteine has a wide range of health benefits and may assist in the production of antioxidants.* NAC may support the kidneys, liver, and lungs and promote healthy immune function.* It may also contribute to healthy skin and support sexual health and brain function, as well as promote a healthy mood.*