The choice of this dosage is based on previous studies (Prado et al., submitted) , in which similar doses that are effective and well tolerated . To enable the process to be double-blind study medications (NAC or placebo ) will be dispensed monthly number and identical formulations and packages sealed by a pharmacist who will participate in the parallel test . Patients will do blood tests for assessment of oxidative stress at baseline will be randomized to use of NAC or placebo and at the final stage of the 12 weeks , when the new assessment and collection of blood for analysis of oxidative stress will be performed . Clinicians who conduct the study will be blinded to allocation of NAC or placebo for each patient .