This study is investigating how N-Acetylcysteine (NAC), an over-the-counter medication, will reduce marijuana use when combined with Contingency Management, a behavioral treatment. It is hypothesized that marijuana dependent adolescents who are treated with NAC will use less marijuana during treatment when compared to adolescents who receive a placebo.

This protocol involves investigation of N-Acetylcysteine (NAC) as a pharmacological treatment for cannabis dependence in adolescents. While recent advances have been made in psychosocial treatments for cannabis dependent adolescents, minimal work has been done to investigate the potential adjunctive role for pharmacotherapy in treatment. NAC is an inexpensive, over-the-counter agent with a favorable tolerability profile in adults and children, in common use since FDA approval in 1963. Preclinical and preliminary clinical research in adults suggests a role for NAC in addiction treatment via glutamate modulation.

Inclusion Criteria:

• Age 13-21 years
• Regular Marijuana smoker meeting DSM-IV criteria for cannabis dependence and seeking marijuana cessation treatment

Exclusion Criteria:

• Allergy or intolerance to NAC
• Pregnancy or lactation
• Use of carbamazepine or nitroglycerine (or any other drug deemed to be hazardous if taken with NAC) within 14 days of study participation
• Current enrollment in treatment for cannabis dependence
• Current substance dependence, other than cannabis or nicotine
• Significant medical or psychiatric illness that may place the participant at increased risk in the judgement of the study physician