The main objective of this study is performance measurement of N - acetylcysteine in prevention of liver toxicity due to anti-TB drugs. The population of study are 60 patients receiving anti-tuberculosis drugs that randomly divided into two groups of 30. During the duration of treatment with anti-tuberculosis drugs, the intervention group, are receiving of acetylcysteine 600 mg orally twice daily for a month and control groups, placebo, 600 mg orally twice per day. Demographic data, primary diagnosis, associated diseases and other medications patients are registered. Blood samples at baseline (before starting anti-TB drugs) and then weekly during the first month of the treatment with anti-TB drugs. Test for liver function (liver enzymes and, if necessary, bilirubin), ESR, CRP is measured. Also using the General Health Assessment Questionnaire (28GHQ) the status of general health in the two groups before and at the end of the first month will be compared. Inclusion criteria: age over 50 years; hemodynamic stability (mean arterial blood pressure >70 mmHg or systolic blood pressure >90mmHg ) Exclusion criteria: history of acute or chronic renal and liver failure accordance with the definitions of relevant, Unavailability of information related to liver function in basic mode, use of N- acetylcysteine orally, injected or inhaled during 1 month before the beginning of the study; Experience has confirmed that the incidence of hypersensitivity reactions following oral, intravenous or inhaled N- acetylcysteine; receiving concomitant drugs or compounds with antioxidant effects such as vitamin C, vitamin E; HIV + patients; use of alcohol