Marijuana is the most commonly used illicit drug in the United States. However, the treatment options for cannabis dependence are limited; notably, no effective pharmacotherapy has been developed. Conceptually, the ideal medication treatment for cannabis dependence would:

1. be safe when administered to patients actively using cannabis
2. reduce cannabis intake and promote abstinence
3. treat the symptoms of cannabis withdrawal
4. reduce craving and relapse risk
5. have a low abuse liability.

Conceptually, the pharmacodynamic and clinical actions of quetiapine suggest that it may be useful for cannabis dependence. By antagonizing dopamine, quetiapine may interfere with the reinforcing effects of cannabis, while serotonin type 2A, histamine type 1, and adrenergic receptor antagonism may reduce cannabis withdrawal symptoms, primarily by sedating and anxiolytic effects. The proposed research project is an open-label pilot study to evaluate the tolerability and ideal target dosing range for quetiapine treatment of cannabis dependence over an eight-week period. The purpose of this pilot study is to obtain preliminary data regarding the potential efficacy, tolerability and safety of quetiapine treatment of cannabis dependence before conducting a larger double-blind trial.

Inclusion Criteria:

1. Between the ages of 18-65
2. Meets DSM-IV criteria for current cannabis dependence
3. Seeking treatment for cannabis dependence
4. Reports using cannabis an average of five days per week over the past 28 days
5. Capable of giving informed consent and complying with study procedures

Exclusion Criteria:

1. Lifetime history of DSM-IV diagnosis of schizophrenia, schizoaffective disorder, or bipolar disorder
2. Current DSM-IV criteria for any other psychiatric disorder that may, according to the investigator's judgment, require either pharmacological or non-pharmacological intervention over the course of the study
3. Receiving prescribed psychotropic medication
4. Known history of allergy, intolerance, or hypersensitivity to quetiapine
5. Pregnancy, lactation, or failure to use adequate contraceptive methods in female patients who are currently engaging in sexual activity with men
6. Unstable medical conditions, such as poorly controlled diabetes or hypertension, which might make participation hazardous
7. Current DSM-IV diagnosis of substance dependence other than cannabis or nicotine dependence
8. Are legally mandated to participate in a substance use disorder treatment program
9. Increased risk for suicide
10. Diabetes (whether controlled or not), hyperglycemia (fasting glucose > 100 mg/dl), obesity (BMI > 30) and elevated lipids (cholesterol > 200 mg/dl; triglycerides > 150 mg/dl).

8 weeks