This study focuses on individuals who have been diagnosed with systemic lupus erythematosus (SLE). The purpose of the study is to determine the medical effectiveness of the antioxidant N-acetylcysteine (NAC). Tiredness is one of the most common conditions in SLE. It is believed that NAC may improve tiredness by increasing the levels of glutathione, which has been found to be lacking in people with SLE. NAC also protects cells from poisonous body-damaging chemicals. Participants will receive either NAC or placebo (inactive substance). Blood donated during study visits will be used to determine whether levels of glutathione increase and immune cell function improves because of taking NAC. The impact of NAC on prednisone usage, liver function, bone marrow function, and overall tiredness will also be evaluated. NAC has been approved by the Food and Drug Administration (FDA) for various conditions, but its use in this study is investigational.