This double-blind study will last a total of 16 weeks. Participants will be randomly assigned to receive either buspirone or placebo for a period of 12 weeks. There will be one follow-up appointment 4 weeks post-intervention. Baseline assessments will include a physical exam and urine and blood tests. Study visits will occur weekly throughout treatment in order to monitor compliance, assess adverse affects, and obtain substance use data. Mood assessment scales, marijuana craving questionnaires, and a withdrawal symptom checklist will be used to gather the data. Urine drug screens will be collected weekly to test for marijuana use. In addition to this, the presence of opioids, cocaine, amphetamines, and benzodiazepines will be tested at baseline, Weeks 6 and 12, and at follow-up. A 10-day supply of medication will be dispensed to participants each week. Meetings for motivational enhancement therapy will last 30 to 90 minutes each and will occur at baseline, Week 2, and Week 4. Participants' perceived quality of life will be measured at baseline and Weeks 6 and 12 to determine the effect of buspirone.