ABSTRACT: Pulmonary tuberculosis is associated with increased oxidative stress, enhanced lipid peroxidation, and decreased glutathione (GSH) levels. N-acetylcysteine (NAC) effectively increases GSH levels, improves lipid peroxidation, and decreases reactive oxygen species levels as reported by earlier studies. Hence, we planned to clinically evaluate the effect of NAC as add-on to Directly Observed Therapy Short-I (DOTS-I) regimen on treatment outcome in PTB with the objectives to study the effect of NAC as an add-on to intensive phase of DOTS-I (2 months) on sputum conversion, radiological improvement, GSH peroxidase (GPx) level, and weight and immunological response compared to placebo add-on at the end of 2 and 6 months.This was a design-prospective, randomized, parallel group, add-on design, placebo-controlled, double-blinded, 24-week study. Parameters studied were sputum acid-fast bacillus examination, radiological improvements, GPx level, weight, and Mantoux response. NAC/placebo was added to DOTS Category I in intensive phase.Totally 48 patients completed the study. In NAC group, 23 patients achieved sputum negativity in 3 weeks while 14 patients in PLACEBO group. There was a significant clearing of infiltration and reduction in cavity size in NAC group compared to placebo at 2 months. At 2 and 6 months, NAC significantly raised GPx level and body weight. In 2 months, the patients with Mix ≤5 became Mx positive (100%) in NAC group while none in placebo group.NAC addition to DOTS-I significantly brings about faster sputum negativity, improves radiological response, weight, raises serum GPx level, and rectifies the deregulated immune response. Thus, NAC may be a useful adjuvant to DOTS in PTB.