After completing all screening evaluations, subjects will receive unblinded N-Acetyl Cysteine 600 mg/day for 2 weeks. The dose will be raised to 1200 mg/day at visit 4 and to 1800 mg/day at visit 6 unless clinical improvement has been attained at a lower dose (clinical improvement will be assessed by the investigator with respect to gambling thoughts, urges and behavior). If it is clinically necessary to modify this schedule (e.g., because of side effects or an adequate response to a lower dose), the dose will be raised more slowly or the target dose will not be reached.